Jiahuan Guo, Huili Feng, Changhui Peng, Huai Chen, X. Xu, Xuehong Ma, Li Li, Daniel Kneeshaw, Hongwua Ruan, Hongqiang Yang, Weifeng Wang. Global Climate Change Increases Terrestrial Soil CH4 Emissions 2023. Global Biogeochem. Cycles 37(1):e2021GB007255
DOI : 10.1029/2021GB007255
Increased greenhouse gas emissions are causing unprecedented climate change, which is, in turn, altering emissions and removals (referring to the oxidation of atmospheric CH4 by methanotrophs within the soil) of the atmospheric CH4 in terrestrial ecosystems. In the global CH4 budget, wetlands are the dominant natural source and upland soils are the primary biological sink. However, it is unclear whether and how the soil CH4 exchanges across terrestrial ecosystems and the atmosphere will be affected by warming and changes in precipitation patterns. Here, we synthesize 762 observations of in situ soil CH4 flux data based on the chamber method from the past three decades related to temperature and precipitation changes across major terrestrial ecosystems worldwide. Our meta-analysis reveals that warming (average warming of +2°C) promotes upland soil CH4 uptake and wetland soil CH4 emission. Decreased precipitation (ranging from −100% to −7% of local mean annual precipitation) stimulates upland soil CH4 uptake. Increased precipitation (ranging from +4% to +94% of local mean annual precipitation) accelerates the upland soil CH4 emission. By 2100, under the shared socioeconomic pathway with a high radiative forcing level (SSP585), CH4 emissions from global terrestrial ecosystems will increase by 22.8 ± 3.6 Tg CH4 yr−1 as an additional CH4 source, which may be mainly attributed to the increase in precipitation over 30°N latitudes. Our meta-analysis strongly suggests that future climate change would weaken the natural buffering ability of terrestrial ecosystems on CH4 fluxes and thus contributes to a positive feedback spiral.
Nicolas Bélanger, Christoforos Pappas, Gabriel Bastien-Beaudet, Catherine Couture, Loïc D'Orangeville, Louis Duchesne, Alexander G. Hurlay, Stefan Kless, Daniel Houle, Fabio Gennaretti, Simon Lebel Desrosiers, Miguel Montoro Girona, Richard L. Peters, Sergio Rossi, Karel St-Amand, Daniel Kneeshaw. Xylem porosity, sapwood characteristics, and uncertainties in temperate and boreal forest water use. 2022. Agric. For. Meteorol. 323:109092
DOI : 10.1016/j.agrformet.2022.109092
Sapwood characteristics, such as sapwood area as well as thermal and hydraulic conductivity, are linked to species-specific hydraulic function and resource allocation to water transport tissues (xylem). These characteristics are often unknown and thus a major source of uncertainty in sap flow data processing and transpiration estimates because bulk rather than species-specific values are usually applied. Here, we analyzed the sapwood characteristics of fifteen common tree species in eastern North America from different taxonomic (i.e., angiosperms and gymnosperms) and xylem porosity groups (i.e., tracheid-bearing, diffuse- or ring-porous species) and we assessed how uncertainties in sapwood characteristics involved in sap flow calculations are propagated in tree water use estimates. We quantified their sapwood area changes with stem diameter (allometric scaling) and thermal conductivity. We combined these measurements with species-specific values of wood density and hydraulic conductivity found in the literature and assessed the role of wood anatomy in orchestrating their covariation. Using an example sap flow dataset from tree species with different xylem porosity, we assessed the sensitivity of tree water use estimates to sapwood characteristics and their interactions. Angiosperms (ring- and diffuse-porous species), with specialized vessels for water transport, showed a steeper relationship (scaling) between tree stem diameter and sapwood area in comparison to gymnosperms (tracheid-bearing species). Gymnosperms (angiosperms) were characterized by lower (higher) wood density and higher (lower) sapwood moisture content, resulting in non-significant differences in sapwood thermal conductivity between taxonomic and xylem porosity groups. Clustering of species sapwood characteristics based on taxonomic or xylem porosity groups and constraining these parameters could facilitate more accurate sap flow calculations and tree water use estimates. When combined with an increasing number of sap flow observations, these findings should improve tree- and landscape-level transpiration estimates, leading to more robust partitioning of terrestrial water fluxes.
Louis Duchesne, Shalini Oogathoo, Daniel Kneeshaw, Daniel Houle. Evaluation of simulated soil moisture and temperature for a Canadian boreal forest. 2022. Agric. For. Meteorol. 323:109078
DOI : 10.1016/j.agrformet.2022.109078
Soil temperature (Tsoil) and soil water (θsoil) are fundamental variables that have an essential role in many processes in forest ecosystems, as well as influencing the tree species distribution and forest composition over time. We tested the Canadian Land Surface Scheme (CLASS) capacity to simulate Tsoil and θsoil in the boreal forest using a sixteen-year data set of daily measurements. Sensitivity analyses were also carried out to evaluate the impact of the thickness of organic layer (TOL), soil texture (percentage sand and clay: PS and PC), drainage parameter (DP), and water freezing point (FP) on simulated Tsoil and θsoil. Finally, the model was also calibrated with a combination of model parameters. CLASS well simulated Tsoil while its performance for θsoil varied by soil horizon and season. In winter particularly, soil liquid water was greatly underestimated because simulated Tsoil was below 0 °C. Nevertheless, simulated θsoil seasonal variation corresponded well with observations. Based on sensitivity analyses, TOL had an important effect on both Tsoil and θsoil. Although PS, PC and DP had almost no effect on Tsoil, their effects on θsoil were substantial. Tsoil increased throughout the year and θsoil increased during the winter with decreasing FP, yet the match between modelled θsoil and observations was not substantially improved. In general, Tsoil was well simulated by CLASS, except for the freezing during winter. Model calibration improves greatly both simulated Tsoil and θsoil, especially during winter in all soil layers. However, despite the model calibration, CLASS still requires improvement for modelling Tsoil and θsoil, hence emphasizing the need to review the equations governing these variables in CLASS.
Shalini Oogathoo, Louis Duchesne, Daniel Houle, Daniel Kneeshaw. Characterizing Seasonal Radial Growth Dynamics of Balsam Fir in a Cold Environment Using Continuous Dendrometric Data: A Case Study in a 12-Year Soil Warming Experiment. 2022. Sensors 22(14):5155
DOI : 10.3390/s22145155
Christopher Michael Gough, Daniel Kneeshaw. Editorial: North Temperate and Boreal Forest Disturbances: The Challenges of Growing in the North 2022. Frontiers in forests and global change 5:956953
DOI : 10.3389/ffgc.2022.956953
Louis De Grandpré, Maryse Marchand, Daniel Kneeshaw, David Paré, Dominique Boucher, Stéphane Bourassa, David Gervais, Martin Simard, Jacob M. Griffin, Deepa Pureswaran. Defoliation-induced changes in foliage quality may trigger broad-scale insect outbreaks. 2022. Community Ecology 5:463
DOI : 10.1038/s42003-022-03407-8
Top-down effects, like predation, are drivers of insect outbreaks, but bottom-up effects, like host nutritional quality, also influence outbreaks and could in turn be altered by insect-caused defoliation. We evaluated the prediction that herbivory leads to a positive feedback on outbreak severity as nutrient concentration in plant tissues increases through improved soil nutrient availability from frass and litter deposition. Over seven years of a spruce budworm outbreak, we quantified litter nutrient fluxes, soil nitrogen availability, and host tree foliar nutrient status along a forest susceptibility gradient. As the outbreak progressed, both soil nutrient fluxes and availability increased which, in turn, improved foliage quality in surviving host trees. This is consistent with boosted insect fitness and increased population density and defoliation as outbreaks grow. Our results suggest that a positive bottom-up feedback to forest ecosystems from defoliation may result in conditions favorable to self-amplifying population dynamics in insect herbivores that can contribute to driving broad-scale outbreaks.
Maryse Marchand, Jeanne Moisan Perrier, Louis-Étienne Robert, Loïc D'Orangeville, Mathieu Bouchard, Daniel Kneeshaw, Louis De Grandpré. Forest Structure and Composition Diverge Following Harvesting Compared to a Spruce Budworm Choristoneura fumiferana (Clem.) Outbreak 2022. Frontiers in forests and global change 5
DOI : 10.3389/ffgc.2022.680262
Balsam fir (Abies balsamea) is the most vulnerable species to the spruce budworm (Choristoneura fumiferana), one of the most devastating defoliators in the world. For decades, pest managers have advocated for reducing its abundance in the landscape to minimize losses to the spruce budworm (SBW). Although reduction of fir occurred during the endemic phase of the SBW cycle, there is little information about the extent to which this general principle (reduction of fir) was applied during an outbreak and whether it occurs at both stand and landscape levels. The objective of this paper is to compare the effect of insect and harvest disturbances on forest structure during the 1970–80s outbreak in Québec. We evaluate whether, (i) forest management activities targeted fir forests and whether patch size of host species influences management or SBW disturbance, (ii) SBW outbreaks and logging have similar or divergent effects on forest composition. Although data are from an earlier outbreak, they are at a scale rarely studied and will be useful in guiding decisions made at larger scales in the current and future outbreaks. Our results show that spruce was targeted preferentially by harvesting (up to 69% of plots) during the outbreak period, while it represented less than one third of plots defoliated by the SBW. On the other hand, fir stands represented up to 75% of plots that were defoliated by the SBW but less than 35% of plots that underwent harvesting. Harvesting targeted large blocks of spruce forest more than large blocks of fir-dominated forest while the opposite was observed for the SBW. In terms of regeneration, SBW tends to reduce fir and favor spruce recruitment, along with non-host species, whereas the opposite tendency was observed following harvesting. In terms of spatial organization of stands, our results support the suggestion that small stands of fir and large stands of spruce undergo the least SBW damage. Thus, in order to attenuate SBW impacts in the future, efforts should be made to ensure that spruce recruitment is favored and that its abundance increases at both the stand and landscape scale.
Mathieu Landry, Patrick James, Steven Kembel, Daniel Kneeshaw. Spruce budworm bacterial communities vary among sites and host tree species in a boreal landscape. 2022. J. of Biogeography 49(2):299-309
DOI : 10.1111/jbi.14299
Abstract Aim Microbial communities often vary spatially in how they assemble and knowledge is lacking about which factors determine the biogeography of host-associated microbiomes. Our aim is to assess the relative importance of spatial, environmental and host-associated factors on microbial community composition of an important defoliating insect. Location Boreal forests in eastern Canada (Quebec, Newfoundland and Labrador). Taxon The eastern spruce budworm (Choristoneura fumiferana) and its associated bacterial communities. Methods We characterized bacterial communities associated with spruce budworm larvae using bacterial 16S rRNA gene amplicon sequencing. We quantified how much of the variation in these bacterial communities could be explained by (1) environmental conditions, (2) the microbiome of foliage the larvae were eating, (3) host tree species and (4) spatial structure as quantified using Moran's Eigenvector Maps (MEMs). Results Budworm larval microbiomes varied significantly among sites and between host tree species. Larvae bacterial community structure was strongly correlated with the structure of bacterial communities taken from paired foliage samples. Spatial structure, foliage bacterial communities and host tree species collectively explained almost one-sixth of the variation in budworm bacterial communities while environmental conditions did not explain variation on their own. Main conclusions Lepidopteran microbiomes primarily originate from the foliage diet. However, subtle differences in microbial communities between larvae and foliage suggest that some bacteria establish and grow in the budworm microbiome, and that dispersal of bacteria from sources other than foliage as well as differences in environmental filtering between larval bodies and foliage play a role in the assembly of the budworm microbiome. While spatial location and spatial structure were also important drivers of spruce budworm bacterial community composition, none of the environmental variables we measured could explain the variation among sites, and identifying the drivers of this spatial variation remains an open question that will need to be addressed by future studies.
Jean-François Prieur, Richard Fournier, Murray E. Woods, Rana Parvez, Benoît St-Onge, Daniel Kneeshaw. A Comparison of Three Airborne Laser Scanner Types for Species Identification of Individual Trees. 2022. Sensors 22(1):35
DOI : 10.3390/s22010035
Species identification is a critical factor for obtaining accurate forest inventories. This paper compares the same method of tree species identification (at the individual crown level) across three different types of airborne laser scanning systems (ALS): two linear lidar systems (monospectral and multispectral) and one single-photon lidar (SPL) system to ascertain whether current individual tree crown (ITC) species classification methods are applicable across all sensors. SPL is a new type of sensor that promises comparable point densities from higher flight altitudes, thereby increasing lidar coverage. Initial results indicate that the methods are indeed applicable across all of the three sensor types with broadly similar overall accuracies (Hardwood/Softwood, 83–90%; 12 species, 46–54%; 4 species, 68–79%), with SPL being slightly lower in all cases. The additional intensity features that are provided by multispectral ALS appear to be more beneficial to overall accuracy than the higher point density of SPL. We also demonstrate the potential contribution of lidar time-series data in improving classification accuracy (Hardwood/Softwood, 91%; 12 species, 58%; 4 species, 84%). Possible causes for lower SPL accuracy are (a) differences in the nature of the intensity features and (b) differences in first and second return distributions between the two linear systems and SPL. We also show that segmentation (and field-identified training crowns deriving from segmentation) that is performed on an initial dataset can be used on subsequent datasets with similar overall accuracy. To our knowledge, this is the first study to compare these three types of ALS systems for species identification at the individual tree level.
Huili Feng, Jiahuan Guo, Xuehong Ma, Menghua Han, Hui Sun, Saadatullah Malghani, Huai Chen, Weifeng Wang, Daniel Kneeshaw. Methane emissions may be driven by hydrogenotrophic methanogens inhabiting the stem tissues of poplar. 2022. New Phytologist 233(1):182-193
DOI : 10.1111/nph.17778
Living trees in forests emit methane (CH4) from their stems. However, the magnitudes, patterns, drivers, origins, and biogeochemical pathways of these emissions remain poorly understood. We measured in situ CH4 fluxes in poplar stems and soils using static chambers and investigated the microbial communities of heartwood and sapwood by sequencing bacterial 16S, archaeal 16S, and fungal ITS rRNA genes. Methane emissions from poplar stems occurred throughout the sampling period. The mean CH4 emission rate was 2.7 mg m−2 stem d−1. Stem CH4 emission rate increased significantly with air temperature, humidity, soil water content, and soil CH4 fluxes, but decreased with increasing sampling height. The CO2 reduction and methylotrophic methanogenesis were the major methanogenic pathways in wood tissues. The dominant methanogen groups detected in stem tissues were Methanobacterium, Methanobrevibacter, Rice Cluster I, Methanosarcina, Methanomassiliicoccus, Methanoculleus, and Methanomethylophilaceae. In addition, three methanotrophic genera were identified in the heartwood and sapwood – Methylocystis, Methylobacterium, and Paracoccus. Overall, stem CH4 emissions can originate directly from the internal tissues or co-occur from soils and stems. The co-existence of methanogens and methanotrophs within heartwood and sapwood highlights a need for future research in the microbial mechanisms underlying stem CH4 exchange with the atmosphere.
Martina Sanchez-Pinillos, Phil Comeau, Jiejie Wang, Anthony Taylor, Loïc D'Orangeville, Yan Boulanger, Daniel Kneeshaw. Sequential droughts: a silent trigger of boreal forest mortality 2022. Global Change Biology 28(2):542-556
DOI : 10.1111/gcb.15913
Despite great concern for drought-driven forest mortality, the effects of frequent low-intensity droughts have been largely overlooked in the boreal forest because of their negligible impacts over the short term. In this study, we used data from 6,876 permanent plots distributed across most of the Canadian boreal zone to assess the effects of repeated low-intensity droughts on forest mortality. Specifically, we compared the relative impact of sequential years under low-intensity dry conditions with the effects of variables related to the intensity of dry conditions, stand characteristics, and local climate. Then, we searched for thresholds in forest mortality as a function of the number of years between two forest surveys affected by dry conditions of any intensity. Our results showed that, in general, frequent low-intensity dry conditions had stronger effects on forest mortality than the intensity of the driest conditions in the plot. Frequent low-intensity dry conditions acted as an inciting factor of forest mortality exacerbated by stand characteristics and environmental conditions. Overall, the mortality of forests dominated by shade-tolerant conifers was significantly and positively related to frequent low-intensity dry conditions, supporting, in some cases, the existence of thresholds delimiting contrasting responses to drought. In mixtures with broadleaf species, however, sequential dry conditions had a negligible impact. The effects of frequent dry conditions on shade-intolerant forests mainly depended on local climate, inciting or mitigating the mortality of forests located in wet places and dominated by broadleaf species or jack pine, respectively. Our results highlight the importance of assessing not only climate-driven extreme events but also repeated disturbances of low intensity. In the long term, the smooth response of forests to dry conditions might abruptly change leading to disproportional mortality triggered by accumulated stress conditions. Forest and wildlife managers should consider the cumulative effects of climate change on mortality to avoid shortfalls in timber and habitat.
Shalini Oogathoo, Louis Duchesne, Daniel Kneeshaw, Daniel Houle. Tree transpiration well simulated by the Canadian Land Surface Scheme (CLASS) but not during drought. 2021. Journal of hydrology 127196
DOI : 10.1016/j.jhydrol.2021.127196
Transpiration, a key component of the hydrological cycle, contributes greatly to the climate system by transferring large amount of water from soils to the atmosphere. Its correct representation within Land Surface Schemes in climate models is crucial to provide accurate and reliable climate projections. In this study, transpiration simulated by the Canadian Land Surface Scheme (CLASS) was compared to long-term observations of sap flow measurements in two boreal forest sites of eastern Canada dominated by balsam fir and black spruce. In general, CLASS adequately models daily transpiration during the growing season for most of the years at both sites. During the tree rehydration period (preceding the growing season), modeled transpiration was greatly underestimated because of overestimating the duration of the snowpack, the latter restricting transpiration. Moreover, CLASS did not capture the impact of extreme events on tree physiology and maintained high transpiration rates during a heat stress and a drought. During both observed and simulated drought events, transpiration modeled using CLASS was overestimated, due to insensitivity to substantial decreases in soil water content; modeled transpiration being strictly controlled by atmospheric variables (vapour pressure deficit and radiations). Thus, we also proposed and implemented a new equation that was able to increase the sensitivity of CLASS to decreasing soil water content. However, this equation needs to be further tested on different sites and tree species.
Shalini Oogathoo, Louis Duchesne, Daniel Houle, Daniel Kneeshaw. Tree transpiration well simulated by the Canadian Land Surface Scheme
(CLASS) but not during drought. 2021. Journal of hydrology 604:127196
DOI : 10.1016/j.jhydrol.2021.127196
Transpiration, a key component of the hydrological cycle, contributes greatly to the climate system by transferring large amount of water from soils to the atmosphere. Its correct representation within Land Surface Schemes in climate models is crucial to provide accurate and reliable climate projections. In this study, transpiration simulated by the Canadian Land Surface Scheme (CLASS) was compared to long-term observations of sap flow measurements in two boreal forest sites of eastern Canada dominated by balsam fir and black spruce. In general, CLASS adequately models daily transpiration during the growing season for most of the years at both sites. During the tree rehydration period (preceding the growing season), modeled transpiration was greatly underestimated because of overestimating the duration of the snowpack, the latter restricting transpiration. Moreover, CLASS did not capture the impact of extreme events on tree physiology and maintained high transpiration rates during a heat stress and a drought. During both observed and simulated drought events, transpiration modeled using CLASS was overestimated, due to insensitivity to substantial decreases in soil water content; modeled transpiration being strictly controlled by atmospheric variables (vapour pressure deficit and radiations). Thus, we also proposed and implemented a new equation that was able to increase the sensitivity of CLASS to decreasing soil water content. However, this equation needs to be further tested on different sites and tree species.
Christoforos Pappas, Yves Bergeron, Nicolas Bélanger, Han Y. H. Chen, Philip G. Comeau, Sylvain Delagrange, Olivier Blarquez, Amanda Diochon, Loïc D’Orangeville, Pierre Drapeau, Louis Duchesne, Elise Filotas, Fabio Gennaretti, Benoit Lafleur, Louis De Grandpré, Annie DesRochers, David Langor, François Lorenzetti, Charles Nock, Daniel Houle, Miguel Montoro Girona, Christian Messier, Barb R. Thomas, Simon Lebel Desrosiers, Rongzhou Man, Timothy Work, Daniel Kneeshaw. Smartforests Canada: A Network of Monitoring Plots for Forest Management Under Environmental Change. 2021. Climate-Smart Forestry in Mountain Regions 521-543
DOI : 10.1007/978-3-030-80767-2_16
Monitoring of forest response to gradual environmental changes or abrupt disturbances provides insights into how forested ecosystems operate and allows for quantification of forest health. In this chapter, we provide an overview of Smartforests Canada, a national-scale research network consisting of regional investigators who support a wealth of existing and new monitoring sites. The objectives of Smartforests are threefold: (1) establish and coordinate a network of high-precision monitoring plots across a 4400 km gradient of environmental and forest conditions, (2) synthesize the collected multivariate observations to examine the effects of global changes on complex above- and belowground forest dynamics and resilience, and (3) analyze the collected data to guide the development of the next-generation forest growth models and inform policy-makers on best forest management and adaptation strategies. We present the methodological framework implemented in Smartforests to fulfill the aforementioned objectives. We then use an example from a temperate hardwood Smartforests site in Quebec to illustrate our approach for climate-smart forestry. We conclude by discussing how information from the Smartforests network can be integrated with existing data streams, from within Canada and abroad, guiding forest management and the development of climate change adaptation strategies.
Naizhuo Zhao, Jean-François Prieur, Ying Liu, Eugénie Morasse Lapointe, Alain Paquette, Kate Zinszer, Jérôme Dupras, Paul J. Villeneuve, Daniel G. Rainham, Eric Lavigne, Hong Chen, Matilda van den Bosch, Tor Oiamo, Audrey Smargiassi, Daniel Kneeshaw. Tree characteristics and environmental noise in complex urban settings – A case study from Montreal, Canada. 2021. Environnemental Research 202:111887
DOI : 10.1016/j.envres.2021.111887
Field studies have shown that dense tree canopies and regular tree arrangements reduce noise from a point source. In urban areas, noise sources are multiple and tree arrangements are rarely dense. There is a lack of data on the association between the urban tree canopy characteristics and noise in complex urban settings. Our aim was to investigate the spatial variation of urban tree canopy characteristics, indices of vegetation abundance, and environmental noise levels. Using Light Detection and Ranging point cloud data for 2015, we extracted the characteristics of 1,272,069 public and private trees across the island of Montreal, Canada. We distinguished needle-leaf from broadleaf trees, and calculated the percentage of broadleaf trees, the total area of the crown footprint, the mean crown centroid height, and the mean volume of crowns of trees that were located within 100m, 250m, 500m, and 1000m buffers around 87 in situ noise measurement sites. A random forest model incorporating tree characteristics, the normalized difference vegetation index (NDVI) values, and the distances to major urban noise sources (highways, railways and roads) was employed to estimate variation in noise among measurement locations. We found decreasing trends in noise levels with increases in total area of the crown footprint and mean crown centroid height. The percentages of increased mean squared error of the regression models indicated that in 500m buffers the total area of the crown footprint (29.2%) and the mean crown centroid height (12.6%) had a stronger influence than NDVI (3.2%) in modeling noise levels; similar patterns of influence were observed using other buffers. Our findings suggest that municipal initiatives designed to reduce urban noise should account for tree features, and not just the number of trees or the overall amount of vegetation.
Malcolm Itter, J. William Munger, Loïc D'Orangeville, Andrew D. Richardson, James M. Dyer, David A. Orwig, Yude Pan, Neil Pederson, Daniel Kneeshaw. Peak radial growth of diffuse-porous species occurs during periods of lower water availability than for ring-porous and coniferous trees. 2021. Tree Physiol. 42(2):304–316
DOI : 10.1093/treephys/tpab101
Climate models project warmer summer temperatures will increase the frequency and heat severity of droughts in temperate forests of Eastern North America. Hotter droughts are increasingly documented to affect tree growth and forest dynamics, with critical impacts on tree mortality, carbon sequestration, and timber provision. The growing acknowledgement of the dominant role of drought timing on tree vulnerability to water deficit raises the issue of our limited understanding of radial growth phenology for most temperate tree species. Here, we use well-replicated dendrometer band data sampled frequently during the growing season to assess the growth phenology of 610 trees from 15 temperate species over six years. Patterns of diameter growth follow a typical logistic shape, with growth rates reaching a maximum in June, and then decreasing until process termination. On average, we find that diffuse-porous species take 16–18 days less than other wood-structure types to put on 50% of their annual diameter growth. However, their peak growth rate occurs almost a full month later than ring-porous and conifer species (ca. 24 ± 4 days; mean ± 95% credible interval). Unlike other species, the growth phenology of diffuse-porous species in our dataset is highly correlated with their spring foliar phenology. We also find that the later window of growth in diffuse-porous species, coinciding with peak evapotranspiration and lower water availability, exposes them to a higher water deficit of 88 ± 19 mm (mean ± SE) during their peak growth than ring-porous and coniferous species (15 ± 35 mm and 30 ± 30 mm, respectively). Given the high climatic sensitivity of wood formation, our findings highlight the importance of wood porosity as one predictor of species climatic sensitivity to the projected intensification of the drought regime in the coming decades.
Qiuyu Liu, Robert Schneider, Changhui Peng, Zelin Liu, Xiaolu Zhou, Daniel Kneeshaw, Dominic Cyr. TRIPLEX-Mortality model for simulating drought-induced tree mortality in boreal forests: Model development and evaluation. 2021. Ecological Modelling 455:109652
DOI : 10.1016/j.ecolmodel.2021.109652
Globally, increasing drought-induced tree mortality rates under climate change are projected to have far-reaching effects on forest ecosystems. Among these forest systems, the boreal forest is considered a ‘tipping element’ of the Earth's climate system. This forest biome plays a critical role in ecosystem services, structures and functions while being highly sensitive to drought stress. Although process-based models are important tools in ecological research, very few have yet been developed that integrate advanced physiological mechanisms to simulate drought-induced mortality in boreal forests. Accordingly, based on the process-based TRIPLEX model, this study introduces the new TRIPLEX-Mortality submodule for the Canadian boreal forests at the stand level, that for the first time successfully incorporates two advanced drought-induced physiological mortality mechanisms (i.e., hydraulic failure and carbon starvation). To calibrate and validate the model, 73 permanent sample plots (PSPs) were selected across Canada's boreal forests. Results confirm a good agreement between simulated mortality and mortality observations (R2=0.79; P<0.01; IA=0.94), demonstrating good model performance in simulating drought-induced mortality in boreal forests. Sensitivity analysis indicated that parameter sensitivity increased as drought intensified, and the shape parameter (c) for calculating percentage loss of conductivity (PLC) was the most sensitive parameter (average SI = -3.51) to simulate tree mortality. Furthermore, the results of model input sensitivity analysis also showed that the model can capture changes in mortality under different drought scenarios. Consequently, our model is suitable for simulating drought-induced mortality in boreal forests while also providing new insight into improving model simulations for tree mortality and associated carbon dynamics in a progressively warmer and drier world.
Marion Germain, Daniel Kneeshaw, Mélanie Desrochers, Patrick James, Udayalaksmi Vepakoma, Louis De Grandpré, Jean-François Poulin, Marc-André Villard. Insectivorous songbirds as early indicators of future defoliation by spruce budworm. 2021. Landscape Ecology 36:3013-3027
DOI : 10.1007/s10980-021-01300-z
Although the spatiotemporal dynamics of spruce budworm outbreaks have been intensively studied, forecasting outbreaks remains challenging. During outbreaks, budworm-linked warblers (Tennessee, Cape May, and bay-breasted warbler) show a strong positive response to increases in spruce budworm, but little is known about the relative timing of these responses.
Jeanne Moisan Perrier, Marc-André Villard, Martin-Hugues St-Laurent, Daniel Kneeshaw. Site-infidelity by budworm-linked warblers at the edge of an area defoliated by spruce budworm. 2021. Avian Conservation and Ecology. 16(1):17
DOI : 10.5751/ACE-01847-160117
Most songbird species show some degree of fidelity to their previous breeding location, especially after successful reproduction. However, species associated with highly dynamic food sources (e.g., outbreaking insects) may have to adopt more flexible strategies. Three species (Tennessee Warbler, Leiothlypis peregrina; Cape May Warbler, Setophaga tigrina; and Bay-breasted Warbler, S. castanea ) show strong numerical responses to spruce budworm (Choristoneura fumiferana-SBW) outbreaks. These species, referred to as "budworm-linked warblers", might track SBW larvae through extensive natal dispersal. Then, the superabundance of food during outbreaks would be expected to lead to high breeding productivity which, in turn, should promote breeding site fidelity. Here, we aimed to determine whether budworm-linked warblers were faithful to their previous year's breeding season location and, if so, whether their probability of return was influenced by habitat characteristics such as the density of SBW larvae, stand structure, or landscape structure. We hypothesized that return rate of budworm-linked warblers will be high, as reported in other species of New World warblers, and we predicted that among habitat characteristics, return rate will increase with the density of SBW larvae. We banded 117 budworm-linked warblers (94 % being males) in 75 study plots distributed along a gradient of SBW density and searched for returning individuals within 50 m of their capture sites using song playbacks. Contrary to our hypothesis, resighting rate was very low (0-10.5%). This relative "infidelity" suggests that breeding dispersal of budworm-linked warblers was relatively extensive. Only habitat proportion within an 8-km radius had an important (negative) effect on the probability of resighting Bay-breasted Warbler. Budworm-linked warblers did not exhibit strong site fidelity as adults, but instead performed breeding dispersal movements, presumably to track SBW outbreaks. This strategy may reflect strong spatiotemporal variations in the density SBW larvae. © 2021 by the author(s). Published here under license by the Resilience Alliance.
Rita Sousa Silva, Audrey Smargiassi, Jérôme Dupras, Kate Zinszer, Alain Paquette, Daniel Kneeshaw. Strong variations in urban allergenicity riskscapes due to poor knowledge of tree pollen allergenic potential 2021. Scientific Reports 11, 10196
DOI : 10.1038/s41598-021-89353-7
Exposure to allergenic tree pollen is an increasing environmental health issue in urban areas. However, reliable, well-documented, peer-reviewed data on the allergenicity of pollen from common tree species in urban environments are lacking. Using the concept of ‘riskscape’, we present and discuss evidence on how different tree pollen allergenicity datasets shape the risk for pollen-allergy sufferers in five cities with different urban forests and population densities: Barcelona, Montreal, New York City, Paris, and Vancouver. We also evaluate how tree diversity can modify the allergenic risk of urban forests. We show that estimates of pollen exposure risk range from 1 to 74% for trees considered to be highly allergenic in the same city. This variation results from differences in the pollen allergenicity datasets, which become more pronounced when a city’s canopy is dominated by only a few species and genera. In an increasingly urbanized world, diverse urban forests offer a potentially safer strategy aimed at diluting sources of allergenic pollen until better allergenicity data is developed. Our findings highlight an urgent need for a science-based approach to guide public health and urban forest planning.
Brian Sturtevant, Enrique Doblas-Miranda, Patrick James, Dominique Tardif, Philip J. Burton, Daniel Kneeshaw, Louis De Grandpré. The Vision of Managing for Pest-Resistant Landscapes: Realistic or Utopic? 2021. Forest Entomology
DOI : 10.1007/s40725-021-00140-z
Purpose of Review
Forest managers have long suggested that forests can be made more resilient to insect pests by reducing the abundance of hosts, yet this has rarely been done. The goal of our paper is to review whether recent scientific evidence supports forest manipulation to decrease vulnerability. To achieve this goal, we first ask if outbreaks of forest insect pests have been more severe in recent decades. Next, we assess the relative importance of climate change and forest management–induced changes in forest composition/structure in driving these changes in severity.
Forest structure and composition continue to be implicated in pest outbreak severity. Mechanisms, however, remain elusive. Recent research elucidates how forest compositional and structural diversity at neighbourhood, stand, and landscape scales can increase forest resistance to outbreaks. Many recent outbreaks of herbivorous forest insects have been unprecedented in terms of duration and spatial extent. Climate change may be a contributing factor, but forest structure and composition have been clearly identified as contributing to these unprecedented outbreaks.
Current research supports using silviculture to create pest-resistant forest landscapes. However, the precise mechanisms by which silviculture can increase resistance remains uncertain. Further, humans tend to more often create pest-prone forests due to political, economic, and human resistance to change and a short-sighted risk management perspective that focuses on reactive rather than proactive responses to insect outbreak threats. Future research efforts need to focus on social, political, cultural, and educational mechanisms to motivate implementation of proven ecological solutions if pest-resistant forests are to be favoured by management.
Jeanne Moisan Perrier, Daniel Kneeshaw, Martin-Hugues St-Laurent, Peter Pyle, Marc-André Villard. Budworm-linked warblers as early indicators of defoliation by spruce budworm: A field study 2021. Ecological Indicators 125:107543
DOI : 10.1016/j.ecolind.2021.107543
Outbreaks of eastern spruce budworm (Choristoneura fumiferana; hereafter SBW) are a major natural disturbance in coniferous forests of eastern North America. These outbreaks provide a superabundant source of food for insectivorous birds. Three species, referred to as budworm-linked warblers, exhibit strong positive numerical responses to early increases of SBW density: Tennessee Warbler (Leiothlypis peregrina), Cape May Warbler (Setophaga tigrina), and Bay-breasted Warbler (S. castanea). Their abundance increases even before defoliation is visible from aerial surveys. Budworm-linked warblers may detect new epicenters of SBW outbreaks through natal dispersal, as this movement is typically much more extensive than subsequent (breeding dispersal) movements. Our main objectives were, thus, (1) to determine whether sudden increases in the abundance of budworm-linked warblers could be used to detect early stages of SBW outbreaks, and (2) to examine age-specific responses of budworm-linked warblers to local and landscape-level habitat characteristics, in order to investigate the potential role of natal dispersal in the detection of new epicenters. To do so, we estimated the abundance of each species of budworm-linked warbler in 75 study plots sampling a gradient of SBW density and related them to 7 stand variables and landscape metrics with generalized additive mixed models. We also compared the responses of yearling (second-year; SY) and older (after-second-year; ASY) individuals to the density of SBW larvae and habitat variables at different spatial scales. We captured 31 Tennessee Warblers, 27 Cape May Warblers, and 57 Bay-breasted Warblers. The abundance of all three species of budworm-linked warblers increased with SBW larval density, but the numerical response of Bay-breasted Warbler was initiated earlier and it varied with age. SY individuals tended to be associated with stands supporting lower larval densities than ASY individuals and, as suggested by other authors, Bay-breasted Warbler appeared to be more efficient at exploiting SBW larvae at low density. For that reason, this species represents an early indicator of stands undergoing SBW outbreaks and we propose to use its abundance as an indicator to orient labour-intensive ground surveys of SBW larvae.
Albanie Leduc, Yves Bergeron, Kobra Maleki, Daniel Kneeshaw, Alain Leduc. Advancing and reversing succession as a function of time since
fire and insect outbreaks: An 18 year in situ remeasurement of
changes in forest composition. 2020. J. Veg. Sci. 32(1):e12974
DOI : 10.1111/jvs.12974
In the boreal mixedwood, fire initiates forest succession; however, over time other disturbances such as insect outbreaks cause pulses of mortality and opportunities for recruitment of shade?intolerant species.
What are the respective roles of time since fire and insect outbreaks in driving directional, vs cyclical and retrogressive succession? Do assessments from direct measurements and chronosequence approaches converge? We hypothesise that the chronosequence approach will accurately characterise large?scale compositional patterns especially in younger stands and that direct measurements will better describe small?scale, non?directional changes in succession.
Boreal mixed wood of northwestern Quebec (79°1? W, 48°30? N).
We sampled 469 plots over an 18?year interval (in 1991 and 2009) in mixed hardwood/conifer forests to observe in situ the changes in stands having originated from seven fires covering a 249?year chronosequence.
The combination of the remeasurement and chronosequence analyses validates predictions of forest succession. Our results indicate that time since last fire is the dominant factor explaining forest succession for the first 150 years after fire and globally at the scale of the entire forest, although smaller?scale disturbances such as spruce budworm outbreaks can change the course of forest succession, especially at stand scales.
While time since fire is the dominant driver of forest succession in younger forests, secondary disturbances, such as spruce budworm outbreaks, can advance or reverse forest succession in older forests. This study also serves as a validation of the overall patterns described in spatial chronosequence approaches at the landscape level in fire?dominated systems but highlights that local succession may deviate from the overall pattern especially in older forests or in forests affected by non?stand re?initiating intermediate disturbances.
Shalini Oogathoo, Louis Duchesne, Daniel Houle, Daniel Kneeshaw. Vapour pressure deficit and solar radiation are the major drivers of transpiration of balsam fir and black spruce tree species in humid boreal regions, even during a short-term drought. 2020. Agric. For. Meteorol. 291:108063
DOI : 10.1016/j.agrformet.2020.108063
On vegetation-covered land surfaces, tree transpiration, compared to soil and canopy evaporation, is a major process that sends large amounts of water back to the atmosphere. While the driving forces of tree transpiration have been studied over a range of tree species across an array of ecosystems, no work has been done on balsam fir and black spruce in the humid boreal forest of eastern Canada.We thus studied the relationships between environmental variables and sap flow velocity (as a proxy for transpiration) for these two boreal tree species located at two forest sites in Quebec, Canada over multiple growing seasons (2004 to 2013 for balsam fir and 2006 to 2009 for black spruce). Our results showed that daily sap flow had a strong non-linear relationship with vapour pressure deficit (VPD) for both species. Sap flow was also strongly correlated to solar radiation (Rad) for both species although with slightly weaker relationships than for VPD. Other variables such as daily maximum temperature and precipitation explain a smaller portion of the variance in sap flow while soil water content (SWC) and wind speed had almost no effect. An analysis of the relationships between sap flow and VPD/Rad on an hourly basis over multiple years showed strong diel hysteresis for both species. Contrary to what has been previously proposed, the magnitude of this hysteresis does not seem to relate to the degree of iso/anisohydricity. Finally, our investigation of sap flow relationships to environmental variables during a drought period at the balsam fir site showed that sap flow was only slightly reduced despite a significant decrease in SWC. On the other hand, VPD and Rad remained the main drivers of sap flow. This study emphasizes that VPD and Rad are indeed the major drivers of transpiration during the growing season as well as during drought in humid boreal region.
Lorena Balducci, Angelo Fierravanti, Sergio Rossi, Sylvain Delzon, Daniel Kneeshaw, Annie Deslauriers, Louis De Grandpré. The paradox of defoliation: Declining tree water status with increasing soil water content. 2020. Agric. For. Meteorol. 290:108025
DOI : 10.1016/j.agrformet.2020.108025
Defoliation can enhance tree water status by reducing canopy transpiration under drought. During long-lasting insect outbreaks however, this effect can be transient as reduced foliage affects not only transpiration but also the entire soil-plant-atmosphere continuum. In this study, we investigated the effects of defoliation and vapor pressure deficit (VPD) on plant and soil water status in balsam fir and black spruce defoliated by spruce budworm, Choristoneura fumiferana (Clemens). We sampled 48 fir trees and 36 spruce trees subjected to differing severities of defoliation. In May–September 2014 and 2015, we monitored the relative shoot water content (RWC) and soil volumetric water content (VWC), and midday shoot water potential (?md, only in 2015). We applied linear mixed models (LMMs) to assess changes in RWC, ?md, and VWC to defoliation and VPD and we ran structural equation models (SEM) to determine the causal relationships between the measured variables in relation to defoliation and VPD. In LMMs models, defoliation and VPD, as individual factors, reduced ?md in both balsam fir and pooled species models but did not affect RWC. Defoliation alone increased VWC in balsam fir and in pooled models. We observed no interaction between VPD and defoliation on tree water status, but significant effect on VWC (in balsam fir and pooled models), indicating that both factors had independent and additive effects on plants but not on soil. However, in SEM models, RWC was negatively correlated to defoliation, suggesting a hydraulic safety margin. Under conditions of multiple-years of natural defoliation during a spruce budworm outbreak, the decrease in ?md reflects the amount of internal water capacitance that could be caused by both a lower ?md due to larval feeding and a negative feedback between defoliation and xylem vulnerability.
Zelin Liu, Changhui Peng, Jean-Noël Candau, Timothy Work, Louis De Grandpré, Xiaolu Zhou, Daniel Kneeshaw. Aerial spraying of bacterial insecticides to control spruce budworm
defoliation leads to reduced carbon losses. 2020. Ecosphere 11(1):e02988
DOI : 10.1002/ecs2.2988
Spruce budworm (SBW) outbreaks are a major natural disturbance in boreal forests of eastern North America. During large?scale infestations, aerial spraying of bacterial insecticides is used to suppress local high?density SBW populations. While the primary goal of spraying is the protection of wood volume for later harvest, it should also maintain carbon stored in trees. This study provides the first quantitative analysis of the efficacy of aerial spraying against SBW on carbon dynamics in balsam fir, spruce, and mixed fir–spruce forests. In this study, we used the TRIPLEX?Insect model to simulate carbon dynamics with and without spray applications in 14 sites of the boreal forest located in various regions of Québec. We found that the efficacy of aerial spraying on reducing annual defoliation was greater in the early stage (<5 yr since the outbreak began) of the outbreak than in later (5–10 yr since the outbreak began) stage. Our results showed that more net ecosystem productivity is maintained in balsam fir (the most vulnerable species) than in either spruce or mixed fir–spruce forests following spraying. Also, average losses in aboveground biomass due to the SBW following spraying occurred more slowly than without spraying in balsam fir forests. Our findings suggest that aerial spraying could be used to maintain carbon in conifer forests during SBW disturbances, but that the efficacy of spray programs is affected by host species and stage of the SBW outbreak.
David L.P. Correia, Wassim Bouachir, David Gervais, Deepa Pureswaran, Daniel Kneeshaw, Louis De Grandpré. Leveraging artificial intelligence for large-scale plant phenology studies from noisy time-lapse images. 2020. IEEE Access 8(1):13151-13160
DOI : 10.1109/ACCESS.2020.2965462
Phenology has become a field of growing importance due to the increasingly apparent impacts of climate change. However, the time-consuming, subjective and tedious nature of traditional human field observations have hindered the development of large-scale phenology networks. Such networks are rare and rely on time-lapse cameras and simplistic color indexes to monitor phenology. To automatize rapid, detailed and repeatable analyzes, we propose an Artificial Intelligence (AI) framework based on machine learning and computer vision techniques. Our approach extracts multiple ecologically-relevant indicators from time-lapse digital photography datasets. The proposed framework consists of three main components: (i) a random forest model to automatically select relevant images based on color information; (ii) a convolutional neural network (CNN) to identify and localize open tree buds; and (iii) a density-based spatial clustering algorithm to cluster open bud detections across the time-series. We tested this framework on a dataset including thousands of black spruce and balsam fir tree images captured using our phenological camera network. The performed experiments showed the efficiency of the proposed approach under challenging perturbation factors, such as significant image noise. Our framework is exceedingly faster and more accurate than human analysts, reducing the time-series processing time from multiple days to under an hour. The proposed methodology is particularly appropriate for large-scale and long-term analyzes of ecological imagery datasets. Our work demonstrates that the use of computer vision and machine learning methods represents a promising direction for the implementation of national, continental, or even global plant phenology networks.
Sophie Perigon, Maryse Marchand, Deepa Pureswaran, Dominique Boucher, Daniel Kneeshaw, Martin-Philippe Girardin, Louis De Grandpré. Adverse climatic periods precede and amplify defoliator?induced tree mortality in eastern boreal North America. 2019. Journal of Ecology 107(1):452-467
DOI : 10.1111/1365-2745.13012
- As major alterations are occurring in climate and pest ranges, it is imperative to evaluate their combined contribution to tree mortality in order to propose mitigation measures and limit losses in forest productivity. The objective of this study was to explore the association between declines in tree growth resulting from climatic and biotic (spruce budworm) disturbances, and their interactions on tree mortality of two dominant tree species, Abies balsamea and Picea mariana, of the eastern North?American boreal forest.
- We disentangle the influences of abiotic and biotic components on growth through a combination of model?data comparison techniques. First, we characterized the variability in tree growth and mortality in the study area using a network of tree?ring width measurements collected from living and dead trees. Subsequently, a bioclimatic simulation model was used to estimate the past annual, nonlinear, responses of stand?level net primary production (NPP) to climate variability (period 1902–2012). From these two data sources, we defined the biotic stress events as the variance in the tree?ring data unexplained by the bioclimatic forest growth simulation.
- Throughout the 20th century, two periods of adverse climatic conditions preceded spruce budworm outbreaks episodes and induced tree mortality. Climatic stress events were associated with cold springs, warmer than average summers. We found that past stress history in interaction with tree characteristics and species predisposed trees to mortality. In addition, co?occurring events (climatic and biotic) increased the severity of mortality episodes.
- Synthesis. Our study challenges the belief that spruce budworm outbreak is the primary driver of broad?scale tree mortality in eastern boreal forest. Rather, tree mortality is the result of cumulative events that combine unfavourable conditions for growth, resulting in loss of tree vigour and subsequently, mortality. Co?occurrence of stresses in the future may lead to more severe episodes of mortality, as extreme climatic events become more frequent.
Martina Sanchez-Pinillos, Aitor Ameztegui, Francisco Lloret, Alain Leduc, Lluis Coll, Daniel Kneeshaw. Resistance, Resilience or Change:
Post-disturbance Dynamics of Boreal
Forests After Insect Outbreaks. 2019. Ecosystems 22(8):1886-1901
DOI : 10.1007/s10021-019-00378-6
Understanding and measuring forest resistance and resilience have emerged as key priorities in ecology and management, particularly to maintain forest functioning. The analysis of the factors involved in a forest’s ability to cope with disturbances is key in identifying forest vulnerability to environmental change. In this study, we apply a procedure based on combining pathway analyses of forest composition and structure with quantitative indices of resistance and resilience to disturbances. We applied our approach to boreal forests affected by a major spruce budworm outbreak in the province of Quebec (Canada). We aimed to identify the main patterns of forest dynamics and the environmental factors affecting these responses. To achieve this goal, we developed quantitative metrics of resistance and resilience. We then compared forests with different pre-disturbance conditions and explored the factors influencing their recovery following disturbance. We found that post-outbreak forest dynamics are determined by distinct resistance and resilience patterns according to dominant species and stand composition and structure. Black spruce forests are highly resistant to spruce budworm outbreaks, but this resistance is conditioned by the length of the defoliation period, with long outbreaks having the potential to lead the system to collapse. In contrast, balsam fir forests easily change to a different composition after outbreaks but are highly resilient when mixed with hardwood species. Overall, the severity of the disturbance and the tree species affected are the main drivers contributing to boreal forest resistance and resilience. Our procedure is valuable to understand post-disturbance dynamics of a broad range of communities and to guide management strategies focused on enhancing the resistance and resilience of the system.
Mathieu Neau, Maryse Marchand, Deepa Pureswaran, Daniel Kneeshaw, Louis De Grandpré. Phenological synchrony between eastern spruce budworm and its host trees increases with warmer temperatures in the boreal forest. 2019. Ecology and Evolution 9(1):576-586
DOI : 10.1002/ece3.4779
Climate change is predicted to alter relationships between trophic levels by changing the phenology of interacting species. We tested whether synchrony between two critical phenological events, budburst of host species and larval emergence from diapause of eastern spruce budworm, increased at warmer temperatures in the boreal forest in northeastern Canada. Budburst was up to 4.6 ± 0.7 days earlier in balsam fir and up to 2.8 ± 0.8 days earlier in black spruce per degree increase in temperature, in naturally occurring microclimates. Larval emergence from diapause did not exhibit a similar response. Instead, larvae emerged once average ambient temperatures reached 10°C, regardless of differences in microclimate. Phenological synchrony increased with warmer microclimates, tightening the relationship between spruce budworm and its host species. Synchrony increased by up to 4.5 ± 0.7 days for balsam fir and up to 2.8 ± 0.8 days for black spruce per degree increase in temperature. Under a warmer climate, defoliation could potentially begin earlier in the season, in which case, damage on the primary host, balsam fir may increase. Black spruce, which escapes severe herbivory because of a 2?week delay in budburst, would become more suitable as a resource for the spruce budworm. The northern boreal forest could become more vulnerable to outbreaks in the future.
Annick St-Denis, Daniel Kneeshaw, Christian Messier. Effect of predation, competition, and facilitation on tree survival and growth in abandoned fields: Towards precision restoration. 2018. Forests 9(11):692
DOI : 10.3390/f9110692
Tree seedlings planted in abandoned agricultural fields interact with herb communities through competition, tolerance, and facilitation. In addition, they are subject to herbivory by small mammals, deer or invertebrates. To increase the success of forest restoration in abandoned fields and reduce management costs, we should determine which species are tolerant to or facilitated by herbaceous vegetation and those which require protection from competition and predation. Eight native tree species were planted in plots covered by herbaceous vegetation, plots where herbaceous vegetation was removed, and plots where seedlings were surrounded by an organic mulch mat. Half of the seedlings were protected against small mammal damage. Results showed that two non-pioneer and moderately shade-tolerant species (yellow birch and red oak) were inhibited by herbaceous vegetation. Birch species were particularly affected by small mammal predation. No effects of predation or herbaceous competition were observed for conifer species. Rather, herbaceous vegetation had a positive effect on the survival and the height growth of tamarack (Larix laricina). None of the tested herb communities had a stronger competitive effect on tree growth than another. Restoration of abandoned fields using multi-tree species should be designed at the seedling scale rather than at the site scale to account for different tree responses to predation and competition as well as variable site conditions. An approach resembling precision agriculture is proposed to lower costs and any potential negative impact of more intensive vegetation management interventions. © 2018 by the authors.
Louis De Grandpré, Kaysandra Waldron, Mathieu Bouchard, Marilou Beaudet, Jean-Claude Ruel, Christian Hébert, Sylvie Gauthier, Daniel Kneeshaw. Incorporating Insect and Wind Disturbances in a Natural Disturbance-Based Management Framework for the Boreal Forest. 2018. Forests 9(8):471
DOI : 10.3390/f9080471
Natural disturbances are fundamental to forest ecosystem dynamics and have been used for two decades to improve forest management, notably in the boreal forest. Initially based on fire regimes, there is now a need to extend the concept to include other types of disturbances as they can greatly contribute to forest dynamics in some regions of the boreal zone. Here we review the main descriptors—that is, the severity, specificity, spatial and temporal descriptors and legacies, of windthrow and spruce bud worm outbreak disturbance regimes in boreal forests—in order to facilitate incorporating them into a natural disturbance-based forest management framework. We also describe the biological legacies that are generated by these disturbances. Temporal and spatial descriptors characterising both disturbance types are generally variable in time and space. This makes them difficult to reproduce in an ecosystem management framework. However, severity and specificity descriptors may provide a template upon which policies for maintaining post harvesting and salvage logging biological legacies can be based. In a context in which management mainly targets mature and old-growth stages, integrating insect and wind disturbances in a management framework is an important goal, as these disturbances contribute to creating heterogeneity in mature and old-growth forest characteristics.
Zelin Liu, Changhui Peng, Jean-Noël Candau, Timothy Work, Annie DesRochers, Daniel Kneeshaw. Application of machine-learning methods in forest ecology: recent progress and future challenges. 2018. Environ. Rev. 26(4):339-350
DOI : 10.1139/er-2018-0034
L’apprentissage automatique, une branche importante de l’intelligence artificielle, est de plus en plus mis en application dans le domaine des sciences comme l’écologie forestière. Ici, nous examinons et faisons le point sur trois méthodes d’apprentissage automatique généralement utilisées incluant l’apprentissage par arbre de décision, le réseau de neurones artificiels et la machine à vecteurs de support, ainsi que leurs applications au niveau de quatre aspects différents de l’écologie forestière au cours de la dernière décennie. Ces applications incluent : (i) les modèles de répartition des espèces, (ii) les cycles de carbone, (iii) l’évaluation et la prédiction des dangers et (iv) d’autres applications en gestion forestière. Alors que les approches d’apprentissage automatique sont utiles au niveau de la classification, de la modélisation et de la prédiction en recherche dans le domaine de l’écologie forestière, le développement accru des technologies d’apprentissage automatique est limité par le manque de données pertinentes et le « seuil relativement plus élevé » des applications. Cependant, l’utilisation combinée d’algorithmes multiples et de communication et coopération améliorées entre les chercheurs en écologie et les concepteurs d’apprentissage automatique présente toujours des défis importants et des tâches en vue de l’amélioration de la recherche écologique à l’avenir. Nous laissons entendre que les applications futures d’apprentissage automatique en écologie deviendront un outil de plus en plus intéressant pour les écologistes face aux « données massives » et que les écologistes auront accès à plus de types de données tel que le son et la vidéo dans un proche avenir ce qui ouvrira probablement de nouvelles avenues en matière de recherche en écologie forestière. [Traduit par la Rédaction]
Anne Cotton-Gagnon, Louis De Grandpré, Martin Simard, Daniel Kneeshaw. Salvage logging during spruce budworm outbreaks increases defoliation of black spruce regeneration. 2018. For. Ecol. Manage. 430:421-430
DOI : 10.1016/j.foreco.2018.08.011
Although advance regeneration abundance and vigor are critical factors determining future forest composition and productivity, very few studies have focused on how they are affected by spruce budworm (SBW) outbreaks even though they affect millions of hectares of boreal forest on a cyclical basis. Post-SBW salvage logging is often used to reduce economic losses but could interact with the outbreak to affect advance regeneration. This study aims to determine the impact of SBW outbreaks and post-outbreak salvage logging on the defoliation of advance regeneration in mixed coniferous stands of northeastern Canada. Specifically, we assessed the effect of regeneration height and species (balsam fir or black spruce), as well as canopy composition, on the defoliation of advance regeneration. We then evaluated the effect of salvage logging on defoliation sustained by advance regeneration and compared it to the one observed in stands only affected by the SBW. Regeneration height and species, canopy composition and salvage logging all significantly affected defoliation and showed multiple interactions. Taller balsam fir seedlings were three times as defoliated as smaller ones, whereas it was 2.3 times for black spruce. Balsam fir seedlings were 15% more defoliated than black spruce. Seedlings of both species located beneath a balsam fir canopy were also more defoliated (>50% defoliation) than seedlings found under black spruce trees (about 26% defoliation). Salvage logging in black spruce-dominated stands resulted in a ?25% increase in defoliation of tall (2.5?m) black spruce regeneration when compared to non-harvested sites. We speculate that this could increase the fir component in spruce-dominated stands, leading to forests that are more susceptible to future SBW outbreaks. To protect spruce advance regeneration from increased defoliation, salvage harvesting of spruce-dominated stands may thus be delayed until the outbreak has subsided. Long-term studies are needed to determine whether a compositional change occurs or not, particularly in spruce-dominated stands. As a precautionary measure, changes in salvage logging practices may be implemented immediately to avoid potential problems such as decreased black spruce abundance and increased susceptibility to future SBW outbreaks.
Sophie Laliberté, Alain Leduc, Pierre Drapeau, Nicole J. Fenton, Daniel Kneeshaw, Osvaldo Valeria, Yves Bergeron, Timothy Work. Commentaires de l’Institut de recherche sur les forêts et de la Chaire en aménagement forestier durable. 2018. Consultation sur le projet de stratégie nationale de production de bois MFFP 9 p.
À l’été 2018, le Ministère des forêts, de la faune et des parcs (MFFP) a tenu des consultations sur un projet de Stratégie nationale de production de bois. Dans ce document se trouvent les commentaires formulés aux noms de l’Institut de recherche sur les forêts (IRF) et de la Chaire en aménagement forestier durable (AFD). Ils sont structurés en fonction des questions contenues dans le formulaire fourni par le MFFP.
Loïc D'Orangeville, Daniel Houle, Louis Duchesne, Richard P. Philips, Yves Bergeron, Daniel Kneeshaw. Beneficial effects of climate warming on boreal
tree growth may be transitory. 2018. Nature - Communications 9:3213
DOI : 10.1038/s41467-018-05705-4
Predicted increases in temperature and aridity across the boreal forest region have the potential to alter timber supply and carbon sequestration. Given the widely-observed variation in species sensitivity to climate, there is an urgent need to develop species-specific predictive models that can account for local conditions. Here, we matched the growth of 270,000 trees across a 761,100?km2 region with detailed site-level data to quantify the growth responses of the seven most common boreal tree species in Eastern Canada to changes in climate. Accounting for spatially-explicit species-specific responses, we find that while 2?°C of warming may increase overall forest productivity by 13?±?3% (mean?±?SE) in the absence of disturbance, additional warming could reverse this trend and lead to substantial declines exacerbated by reductions in water availability. Our results confirm the transitory nature of warming-induced growth benefits in the boreal forest and highlight the vulnerability of the ecosystem to excess warming and drying.
Philippe Nolet, Daniel Kneeshaw. Extreme events and subtle ecological effects: lessons from
a long-term sugar maple–American beech comparison. 2018. Ecosphere 9(7):e02336
DOI : 10.1002/ecs2.2336
Increasing extreme events that are related to global change are expected to affect the dynamics of forest ecosystems. If disruptive stressors (e.g., insects, drought) affect tree vigor without causing mortality, the ecological effects may be subtle, making subsequent ecosystem dynamics more difficult to predict than in the case of disturbances causing death. Based on the literature and our personal observations, we expected that such a subtle change could have occurred in the dynamics between sugar maple and American beech. We implemented a targeted paired?sampling design (1) to verify whether a change occurred (gradual or abrupt, recovered or not) in the growth dynamics between the two species over a 57?yr period, (2) to identify the likely causes of this change, and (3) to investigate whether such changes could trigger other long?time ecological consequences. We found that sugar maple growth was negatively affected by an extreme event (or a few events) between 1986 and 1989, while American beech was not affected. Twenty years after the 1986–1989 abrupt growth decrease, sugar maple (1) had a slower growth than American beech, although it was previously similar, (2) did not respond to monthly climatic variations as it did prior to the abrupt growth decrease, and (3) had lower resilience when faced with a new stress event. Overall, our study, besides showing that extreme events with subtle effects may change the dynamics of an ecosystem, also illustrates that these events may accelerate ecosystem misadaptation to climate. Fine?scale targeted monitoring is essential to complement broad?scale monitoring to detect such misadaptations in a global change context.
Parinaz Rahimzadeh-Bajgiran, Aaron R. Weiskittel, David MacLean, Daniel Kneeshaw. Detection of annual spruce budworm defoliation and severity classification using Landsat imagery. 2018. Forests 9(6):357
DOI : 10.3390/f9060357
Spruce budworm (SBW) is the most destructive forest pest in eastern forests of North America. Mapping annual current-year SBW defoliation is challenging because of the large landscape scale of infestations, high temporal/spatial variability, and the short period of time when detection is possible. We used Landsat-5 and Landsat-MSS data to develop a method to detect and map SBW defoliation, which can be used as ancillary or alternative information for aerial sketch maps (ASMs). Results indicated that Landsat-5 data were capable of detecting and classifying SBW defoliation into three levels comparable to ASMs. For SBW defoliation classification, a combination of three vegetation indices, including normalized difference moisture index (NDMI), enhanced vegetation index (EVI), and normalized difference vegetation index (NDVI), were found to provide the highest accuracy (non-defoliated: 77%, light defoliation: 60%, moderate defoliation: 52%, and severe defoliation: 77%) compared to using only NDMI (non-defoliated: 76%, light defoliation: 40%, moderate defoliation: 43%, and severe defoliation: 67%). Detection of historical SBW defoliation was possible using Landsat-MSS NDVI data, and the produced maps were used to complement coarse-resolution aerial sketch maps of the past outbreak. The method developed for Landsat-5 data can be used for current SBW outbreak mapping in North America using Landsat-8 and Sentinel-2 imagery. Overall, the work highlights the potential of moderate resolution optical remote sensing data to detect and classify fine-scale patterns in tree defoliation. © 2018 by the authors.
Sophie Perigon, Maryse Marchand, Deepa Pureswaran, Dominique Boucher, Daniel Kneeshaw, Louis De Grandpré, Martin-Philippe Girardin. Adverse climatic periods precede and amplify defoliator?induced tree mortality in eastern boreal North America. 2018. Journal of Ecology 107(1):452-467
DOI : 10.1111/1365-2745.13012
1.As major alterations are occurring in climate and pest ranges, it is imperative to evaluate their combined contribution to tree mortality in order to propose mitigation measures and limit losses in forest productivity. The objective of this study was to explore the association between declines in tree growth resulting from climatic and biotic (spruce budworm) disturbances, and their interactions on tree mortality of two dominant tree species, Abies balsamea and Picea mariana, of the eastern North?American boreal forest.
2.We disentangle the influences of abiotic and biotic components on growth through a combination of model?data comparison techniques. First, we characterized the variability in tree growth and mortality in the study area using a network of tree?ring width measurements collected from living and dead trees. Subsequently, a bioclimatic simulation model was used to estimate the past annual, non?linear, responses of stand?level net primary production (NPP) to climate variability (period 1902?2012). From these two data sources, we defined the biotic stress events as the variance in the tree?ring data unexplained by the bioclimatic forest growth simulation.
3.Throughout the 20th century, two periods of adverse climatic conditions preceded spruce budworm outbreaks episodes and induced tree mortality. Climatic stress events were associated with cold springs, warmer than average summers. We found that past stress history in interaction with tree characteristics and species predisposed trees to mortality. In addition, co?occurring events (climatic and biotic) increased the severity of mortality episodes.
4.Synthesis: Our study challenges the belief that spruce budworm outbreak is the primary driver of broad?scale tree mortality in eastern boreal forest. Rather, tree mortality is the result of cumulative events that combine unfavourable conditions for growth, resulting in loss of tree vigour and subsequently, mortality. Co?occurrence of stresses in the future may lead to more severe episodes of mortality, as extreme climatic events become more frequent.
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Deepa Pureswaran, Mathieu Bouchard, Louis De Grandpré, Daniel Kneeshaw. Climate-induced range shifts in boreal forest pests: ecological, economic, and social consequences. 2018. Can. J. For. Res. 48(3):v-vi
DOI : 10.1139/cjfr-2018-0058
Climate change is causing northward shifts in species ranges. For mobile species such as insects, this will increase their access to forest ecosystems where in the past their presence and impact was limited. Range expansion and increases in outbreak severity of forest pests have been documented in Europe and North America (Jepsen et al. 2008; Bentz et al. 2010). Temperature-mediated phenological changes and trophic interactions among host trees, herbivorous insects, and their natural enemies are linked to the long-term effects of range expansion on boreal ecosystems. The degree to which temperate and boreal forest ecosystems are resilient to novel disturbance regimes will have direct consequences on the provisioning of goods and services from these forests and on long-term forest management planning. These concerns were the impetus for the organization of a workshop on climate-induced range shifts in boreal forest pests. Contributions to this special feature are selected papers from the International Union of Forest Research Organizations (IUFRO) workshop held in July 2016 in northeastern Quebec. The workshop was organized around five themes related to the consequences of range shifts of boreal forest insect pests: (1) plant–insect phenology, (2) species range expansions, (3) ecosystem response to changes in disturbance regimes, (4) interactions among disturbances, and (5) forest management and adaptation to change.
Justin Maxwell, Loïc D'Orangeville, Neil Pederson, Travis Logan, Colin M. Beier, Daniel Druckenbord, Louis Duchesne, Dominique Arseneault, Shawn Fraver, François Girard, Daniel Kneeshaw, Joshua Halman, Chris Hansen, Justin L. Hart, Henrik Hartmann, Margot Kaye, David Leblanc, Daniel Houle, Stefano Manzoni, Shelly Rayback, Rock Ouimet, Christine R. Rollinson, Richard P. Philips. Drought timing and local climate determine the sensitivity of eastern temperate forests to drought. 2018. Global Change Biology 24(6):2339-2351
DOI : 10.1111/gcb.14096
Louis-Étienne Robert, Brian Sturtevant, Barry J. Cook, Patrick James, Philip A. Townsend, Peter, T. Wolter, Marie-Josée Fortin, Daniel Kneeshaw. Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm Choristoneura fumiferana. 2018. Ecography 41(9):1556-1571
DOI : 10.1111/ecog.03553
Landscape-level forest management has long been hypothesized to affect forest insect outbreak dynamics, but empirical evidence remains elusive. We hypothesized that the combination of increased hardwood relative to host tree species, prevalence of younger forests, and fragmentation of those forests due to forest harvesting legacies would reduce outbreak intensity, increase outbreak frequency, and decrease spatial synchrony in spruce budworm Choristoneura fumiferana outbreaks. We investigated these hypotheses using tree ring samples collected across 51 sites pooled into 16 subareas distributed across a large ecoregion spanning the international border between Ontario (Canada), and Minnesota (USA). This ecoregion contains contrasting land management zones with clear differences in forest landscape structure (i.e. forest composition and spatial configuration) while minimizing the confounding influence of climate. Cluster analyses of the 76-yr time-series generally grouped by subareas found within the same land management zone. Spatial nonparametric covariance analysis indicated that the highest and lowest degree of spatial synchrony of spruce budworm outbreaks were found within unmanaged wilderness and lands managed at fine spatial scales in Minnesota, respectively. Using multivariate analysis, we also found that forest composition, configuration, and climate together accounted for a total of 40% of the variance in outbreak chronologies, with a high level of shared variance between composition and configuration (13%) and between composition and climate (9%). At the scale of our study, climate on its own did not explain any of the spatial variation in outbreaks. Outbreaks were of higher frequency, lower intensity, and less spatially synchronized in more fragmented, younger forests with a lower proportion of host species, with opposing outbreak characteristics observed in regions characterised by older forests with more concentrated host species. Our study is the first quantitative evaluation of the long-standing ‘silvicultural hypothesis’ of spruce budworm management specifically conducted at a spatio-temporal scale for which it was intended.
Philippe Nolet, Daniel Kneeshaw, Martin Béland, Christian Messier. Comparing the effects of even- and uneven-aged silviculture on ecological diversity and processes: A review. 2018. Ecology and Evolution 8(2):1217-1226
DOI : 10.1002/ece3.3737
With an increasing pressure on forested landscapes, conservation areas may fail to maintain biodiversity if they are not supported by the surrounding managed forest matrix. Worldwide, forests are managed by one of two broad approaches—even- and uneven-aged silviculture. In recent decades, there has been rising public pressure against the systematic use of even-aged silviculture (especially clear-cutting) because of its perceived negative esthetic and ecological impacts. This led to an increased interest for uneven-aged silviculture. However, to date, there has been no worldwide ecological comparison of the two approaches, based on multiple indicators. Overall, for the 99 combinations of properties or processes verified (one study may have evaluated more than one property or process), we found nineteen (23) combinations that clearly showed uneven-aged silviculture improved the evaluated metrics compared to even-aged silviculture, eleven (16) combinations that showed the opposite, and 60 combinations that were equivocal. Furthermore, many studies were based on a limited study design without either a timescale (44 of the 76) or spatial (54 of the 76) scale consideration. Current views that uneven-aged silviculture is better suited than even-aged silviculture for maintaining ecological diversity and processes are not substantiated by our analyses. Our review, by studying a large range of indicators and many different taxonomic groups, also clearly demonstrates that no single approach can be relied on and that both approaches are needed to ensure a greater number of positive impacts. Moreover, the review clearly highlights the importance of maintaining protected areas as some taxonomic groups were found to be negatively affected no matter the management approach used. Finally, our review points to a lack of knowledge for determining the use of even- or uneven-aged silviculture in terms of both their respective proportion in the landscape and their spatial agency.
Louis Duchesne, Rock Ouimet, Loïc D'Orangeville, Daniel Houle, Daniel Kneeshaw. Extracting coherent tree-ring climatic signals across spatial scales from extensive forest inventory data. 2017. PlosOne 12(12):e0189444
DOI : 10.1371/journal.pone.0189444
Increasing access to extensively replicated and broadly distributed tree-ring collections has led to a greater use of these large data sets to investigate climate forcing on tree growth. However, the number of chronologies added to large accessible databases is declining and few are updated, while chronologies are often sparsely distributed and are more representative of marginal growing environments. On the other hand, National Forest Inventories (NFI), although poorly replicated at the plot level as compared to classic dendrochronological sampling, contain a large amount of tree-ring data with high spatial density designed to be spatially representative of the forest cover. We propose an a posteriori approach to validating tree-ring measurements and dating, selecting individual tree-ring width time series, and building average chronologies at various spatial scales based on an extensive collection of ring width measurements of nearly 94,000 black spruce trees distributed over a wide area and collected as part of the NFI in the province of Quebec, Canada. Our results show that reliable signals may be derived at various spatial scales (from 37 to 583,000 km²) from NFI increment core samples. Signals from independently built chronologies are spatially coherent with each other and well-correlated with independent reference chronologies built at the stand level. We thus conclude that tree-ring data from NFIs provide an extraordinary opportunity to strengthen the spatial and temporal coverage of tree-ring data and to improve coordination with other contemporary measurements of forest growth to provide a better understanding of tree growth-climate relationships over broad spatial scales.
Cynthia Patry, Isabelle Aubin, Daniel Kneeshaw, Christian Messier. Intensive forestry filters understory plant traits over time and space in boreal forests. 2017. Forestry 90(3):436-444
DOI : 10.1093/forestry/cpx002
Because of their scarcity, protected areas alone cannot maintain biodiversity. Therefore, it is necessary to create conditions appropriate for plants and wildlife in managed landscapes. We compared the effects of different intensities of forest management on functional responses of vascular understory plants using the fourth-corner method. We analysed functional community composition along a management gradient that spanned semi-natural forests to extensively managed forests (naturally regenerated cuts) to intensively managed forests (planted forests) in Canada. Results showed trait filtering along the gradient of forest management intensity. In natural and extensively managed forests, where forest retention was high in time and space, persistence traits (e.g. perennial geophytes or chamaephytes, non-leafy stem foliage structure) were maintained. At the opposite end of the gradient, in intensively managed plantations where forest retention elements (e.g. amount of dead wood) were reduced, trait filtering led to species associated with colonization, such as tall species with limited lateral extension. These results suggest that intensive forestry conducted over a large extent may change the functional composition of understory plants.
Fidèle Bognounou, Deepa Pureswaran, Daniel Kneeshaw, Louis De Grandpré. Temporal variation in plant neighborhood effects on the defoliation
of primary and secondary hosts by an insect pest. 2017. Ecosphere 8(3):e01759
DOI : 10.1002/ecs2.1759
Plant neighborhood effects on herbivore damage have been observed in many systems although few studies have assessed the different component effects of the neighborhood (conspecific neighbors vs. heterospecific neighbors) on defoliation. No earlier studies have monitored how temporal scale influences neighborhood effects. We tested hypotheses on resource concentration/dilution and associational effects in the eastern spruce budworm (Choristoneura fumiferana)–forest system over a 10-yr period across different stands including stands dominated by highly vulnerable hosts (balsam fir), stands dominated by a species with low vulnerability (black spruce), and mixed composition stands (fir and spruce). We observed persistent resource concentration effects on the primary host (balsam fir) during the increasing phase of the outbreak in balsam fir-dominated and mixed stands, while both resource dilution and associational susceptibility effects were observed on the secondary host (black spruce) and the strength of associational susceptibility increased with an increase in resource dilution. We did not observe associational effects on the primary host in mixed and secondary host-dominated stands but in stands dominated by the primary host, we observed associational resistance when the resource was highly depleted. Therefore, the complexity of neighborhood effects suggests that future studies should consider the separate effects of conspecific and heterospecific neighbors, as well as changes through time in order to predict herbivore damage in different systems, and provide better preventive and reactive strategies to manage herbivore outbreaks.
Annick St-Denis, Suzanne W. Simard, Isabelle Laforest-Lapointe, Nicolas Bélanger, Daniel Kneeshaw, Christian Messier. Species-specific responses to forest soil inoculum in planted trees in an abandoned agricultural field. 2017. Applied Soil Ecology 12:1-10
DOI : 10.1016/j.apsoil.2016.12.008
Tree plantations are commonly used to restore abandoned agricultural fields with varying degrees of success. Agricultural soils differ from forest soils in nutrient availability and microbial communities. The objective of this study was to test the effect of adding small amounts of forest soil on the survival, growth and rates of mycorrhizal fungal colonization of trees planted in an abandoned agricultural field over the crucial first three growing seasons. Seedlings of two arbuscular mycorrhizal (AM) and two ectomycorrhizal (EM) tree species were planted in an abandoned agricultural field. Soil inocula were taken from four forest stands, each dominated by one of the planted species. Half of the soil samples were sterilized before inoculation to distinguish microbial from nutrient effects. The effect of the quantity of soil inoculum added was tested using 300 and 1500 ml of forest soil. Tree mortality was low and did not vary between treatments. The growth of EM tree species responded, positively or negatively, to forest soil inoculation. A negative feedback was detected on the growth of red oak seedlings inoculated with red oak soil. Seedlings inoculated with EM sterilized soils were smaller than control seedlings, presumably due to lower nutrient availability of EM forest soils compared to agricultural field soil. The majority of the effects, either positive or negative, were observed the first year. After three seasons of growth, only yellow birch seedlings that had received 1500 ml of non-sterilized red oak soil still benefited from soil inoculation. More research is needed in nutrient-limited soils to determine whether inoculation would have greater or longer term benefits on tree survival and growth. © 2016
Loïc D'Orangeville, Louis Duchesne, Benoit Côté, Neil Pederson, Daniel Kneeshaw, Daniel Houle. Northeastern North America as a potential refugium for boreal forests in a warming climate. 2016. Science 352(6292):1452-1455.
DOI : 10.1126/science.aaf4951
High precipitation in boreal northeastern North America could help forests withstand the expected temperature-driven increase in evaporative demand, but definitive evidence is lacking. Using a network of tree-ring collections from 16,450 stands across 583,000 km2 of boreal forests in Québec, Canada, we observe a latitudinal shift in the correlation of black spruce growth with temperature and reduced precipitation, from negative south of 49°N to largely positive to the north of that latitude. Our results suggest that the positive effect of a warmer climate on growth rates and growing season length north of 49°N outweighs the potential negative effect of lower water availability. Unlike the central and western portions of the continent’s boreal forest, northeastern North America may act as a climatic refugium in a warmer climate.
Aitor Ameztegui, Gauthier Ligot, Lluis Coll, Benoit Courbaud, Daniel Kneeshaw. Tree light capture and spatial variability of
understory light increase with species mixing and
tree size heterogeneity. 2016. Can. J. For. Res. 46(7):968-977
DOI : 10.1139/cjfr-2016-0061
Mixed and multi-layered forest ecosystems are sometimes more productive than monospecific and single-layered ones. It has
been suggested that trees of different species and sizes occupy complementary positions in space which would act as a
mechanism to increase canopy light interception and wood production. However, greater canopy light interception reduces
the average amount and variability of transmitted radiation offering fewer opportunities for all species to regenerate and to
maintain forest heterogeneity in the long-run. We investigated whether increasing overstory heterogeneity indeed results
in greater canopy light interception and lower variability in transmittance. We modeled the three-dimensional structure of
forest stands with 3 typical forest structures, 10 mixtures of four tree species, and 3 different basal areas. We used the forest
light interception model SAMSARALIGHT and performed three-way analyses of covariance to analyze the effects of the
three varied components of forest heterogeneity. We found no evidence that increasing heterogeneity increases canopy light
interception. In contrast, homogeneous stands intercept more light than heterogeneous stands. Variability in transmittance
increased in some cases with compositional heterogeneity and, to a lesser extent, with tree size inequalities. The advantage
of heterogeneous forests is in opportunities for natural regeneration rather than in opportunities to enhance canopy light
Hugh Power, Valérie Lemay, Frank Berninger, Daniel Kneeshaw. Pipe-model ratio distributions and branch foliage biomass: differences between two sympatric spruce species. 2016. Scand. J. For. Res. 31(1):8-18
DOI : 10.1080/02827581.2015.1068369
The foliage biomass–sapwood relationship (the pipe model) is critical for tree growth and is used in tree growth models for understanding the implications of this structural relationship on the allocation of resources. In this research, we compared this relationship for two commercially important and sympatric species, black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss). At locations in eastern Canada, 57 black and 50 white spruce trees were destructively sampled to obtain foliage biomass, crown structure, and tree stem measures. Using a model-based approach, we compared foliage biomass–branch basal area and foliage biomass–sapwood relationships at the tree and disk (i.e. along the tree stem) levels (i.e. pipe-model ratios) between these two species. We found that (i) branch foliage biomass–branch basal area was greater for black spruce than white spruce and (ii) pipe-model ratios along the tree stem given tree size were greater for black spruce than for white spruce. We attributed these differences to: (i) greater shade tolerance and leaf longevity of black spruce; (ii) slower growth rates of black spruce; and (iii) differing hydraulic strategies and mechanical requirements.
Brian Sturtevant, Barry J. Cook, Deepa Pureswaran, David MacLean, Daniel Kneeshaw, Louis De Grandpré, Timothy Work. Insect disturbances in forest ecosystems. 2015. Routledge Handbook of Forest Ecology pp. 93-113.
Mathieu Morin, Frédérick Doyon, Véronique Yelle, Anne Blondlot, Héloïse Le Goff, Daniel Kneeshaw, Pierre Bernier, Daniel Houle. Climate change and the forest sector: Perception of principal
impacts and of potential options for adaptation. 2015. For. Chron. 91(4):395-406
DOI : 10.5558/tfc2015-069
Les impacts des changements climatiques (CCs) sur la forêt sont déjà observés et iront en s'amplifiant dans le futur. Dans ce contexte, il importe de comprendre comment les communautés et l'industrie forestière seront affectées. Des professionnels du secteur forestier québécois ont été consultés lors d'un atelier afin de recueillir leurs perceptions des impacts potentiels des CCs et des possibles mesures d'adaptation. Les préoccupations touchaient les écosystèmes naturels, ainsi que les collectivités et l'industrie forestière. Les impacts identifiés incluaient l'augmentation des évènements météorologiques extrêmes et des perturbations naturelles, une diminution quantitative et qualitative du bois, ainsi que de plus grandes difficultés d'accès aux territoires et des coûts additionnels pour les opérations. Les mesures d'adaptation pourraient comprendre de nouvelles règlementations, une meilleure sensibilisation aux enjeux, et des ajustements locaux et régionaux dans la gestion et les opérations. Les barrières à l'adaptation identifiées incluaient une faible compréhension des enjeux au niveau des intervenants du milieu forestier, ainsi qu'un manque de soutien scientifique, de transfert des connaissances, et de leadership à l’échelle régionale. Cette synthèse aidera à orienter les besoins en matière de planification et de gestion et à identifier des solutions pour augmenter la capacité d'adaptation du secteur forestier.
Dominique Boucher, Louis De Grandpré, Daniel Kneeshaw, Benoît St-Onge, Jean-Claude Ruel, Kaysandra Waldron, Jean-Martin Lussier. Effects of 80 years of forest management on landscape structure and pattern in the eastern Canadian boreal forest. 2015. Landscape Ecology 30(10):1913-1929
DOI : 10.1007/s10980-015-0220-6
Forest management alters patterns generated by natural disturbances, particularly in ecosystems with infrequent fires. Management effects can differ according to spatial scale and affect ecological processes.
To assess the effect of 80 years of forest management at both the landscape and burn/harvest scales on forest age, composition, density, spatial pattern and heterogeneity.
Forest inventory maps and satellite images were used to compare two contiguous landscapes, respectively managed and unmanaged, of the eastern boreal forest of Canada, in a region with infrequent fires. Burns and harvests occurring from 1920–1950 were also compared.
In addition to reducing the proportion of old-growth stands in the landscape, forest management changed forest composition at both scales, favouring the late-successional species balsam fir. Landscape metrics indicated that old-growth forests and spruce-dominated ones were more fragmented, less connected, and confined to smaller patches in the managed landscape than in the unmanaged one. Forest management increased heterogeneity at the landscape scale, but decreased it at the burn/harvest scale. Logging had a homogenizing effect at the burn/harvest scale by attenuating the effect of the physical environment on forest density.
This study provides knowledge to help reduce effects of forest management at both scales. In this forest region with low fire recurrence, the goal should be to manage for greater forest heterogeneity at the burn/harvest scale whereas, at the landscape scale, restoration strategies should aim to create large contiguous patches of coniferous forests to increase spatial continuity as these were reduced by past management activities.
Mario Larouche, Daniel Kneeshaw, Hugo Asselin. Assessing forest management scenarios on an Aboriginal territory through simulation modeling. 2015. For. Chron. 91(4): 426-435
DOI : 10.5558/tfc2015-072
La principale stratégie d'aménagement en forêt boréale—les coupes agglomérées (CA)—est de plus en plus critiquée par plusieurs parties prenantes, incluant les peuples autochtones. Deux stratégies alternatives ont été proposées: les coupes dispersées (CD) et l'aménagement écosystémique (AE). Nous avons modélisé les effets à long terme et à l’échelle du paysage de CA, CD et AE sur un ensemble d'indicateurs d'aménagement forestier durable liés aux valeurs d'une communauté autochtone: (1) la structure d’âge de la forêt; (2) la configuration spatiale des peuplements forestiers; (3) la densité du réseau routier; et, (4) la perte d'habitat forestier due aux coupes totales. AE a créé une structure d’âge plus proche de celle qui résulterait d'un régime naturel de perturbations, comparativement à CA et CD. Les blocs de coupe étaient répartis plus uniformément sur le territoire avec AE et CD. Le réseau routier était moins étendu et se développait moins vite avec AE, réduisant ainsi le potentiel de conflits entre usagers de la forêt. AE a aussi maintenu plus de couvert forestier (et donc plus d'habitat faunique potentiel) que CA ou CD. Le scenario AE a obtenu de meilleurs scores pour les quatre indicateurs mesurés, en partie parce que les contraintes imposées à l'exercice de modélisation ont résulté en moins de coupes que dans les autres scénarios. La possibilité forestière annuelle devrait par conséquent être un facteur clé à considérer pour assurer une meilleure conformité aux critères autochtones d'aménagement forestier durable.
Philippe Nolet, Sylvain Delagrange, Kim Bannon, Christian Messier, Daniel Kneeshaw. Liming has a limited effect on sugar maple – American beech dynamics compared with beech sapling elimination and canopy opening. 2015. Can. J. For. Res. 45:1376-1386
DOI : 10.1139/cjfr-2015-0010
Les forêts nord-américaines dominées par l’érable à sucre (ERS, Acer saccharum Marsh.) sont de plus en plus influencées par des modifications des conditions environnementales d’origine anthropique. Pour remédier à cette situation, des traitements sylvicoles adaptés sont nécessaires. Même s’il est généralement accepté que la santé de l’ERS est liée à la fertilité du sol et qu’il y a une littérature abondante sur la dynamique de la régénération des peuplements composés d’ERS et de hêtre à grandes feuilles (HEG, Fagus grandifolia Ehrh.) en fonction de la disponibilité de lumière, l’interaction entre ces deux facteurs a rarement été étudiée. Notre objectif principal était donc de vérifier le rôle potentiel d’une interaction entre la lumière et le sol sur la dynamique des peuplements composés d’ERS et de HEG. Nous avons utilisé un dispositif factoriel à trois facteurs (intensité de récolte, chaulage et élimination des gaules de hêtre) pour tester cette interaction. Nos résultats montrent que la croissance radiale des arbres et des gaules d’ERS et de HEG était positivement influencée par l’ouverture du couvert, mais pas par le chaulage. Le chaulage n’a pas favorisé les semis de HEG, mais il a favorisé ceux d’ERS dans des situations spécifiques d’ouverture du couvert, ce qui confirme, bien que partiellement, l’hypothèse de l’interaction entre la lumière et le sol. Globalement, le chaulage a eu des effets très limités sur la dynamique des peuplements composés d’ERS et de HEG comparativement aux traitements d’ouverture du couvert et d’élimination des gaules de HEG. Nous ne préconisons pas l’utilisation généralisée du chaulage puisque les autres stratégies sylvicoles testées ont produit des résultats plus prometteurs pour favoriser l’ERS aux dépens du HEG. [Traduit par la Rédaction]
Guillaume Sainte-Marie, David MacLean, Chris R. Hennigar, Daniel Kneeshaw. Estimating forest vulnerability to the next spruce budworm outbreak: will past silvicultural efforts pay dividends? 2015. Can. J. For. Res. 45(3):314-324
DOI : 10.1139/cjfr-2014-0344
Les traitements sylvicoles recommandés pour réduire les dommages lors d’épidémies de la tordeuse des bourgeons de l’épinette (TBE; Choristoneura fumiferana Clemens) incluent la réduction de l’abondance et de l’âge du sapin (Abies balsamea (L.) Mill.) et l’augmentation de l’abondance d’épinettes (Picea spp.) et de feuillus. Afin d’évaluer l’effet de ces mesures sur l’approvisionnement en bois, nous avons évalué de 1985 à 2004 les caractéristiques, l’historique des perturbations et l’approvisionnement en résineux d’une forêt de l’est du Québec sous aménagement intensif et pendant une épidémie majeure de TBE. Pendant cette période, l’âge moyen des peuplements a chuté de 55 à 51 ans, la proportion de peuplements de sapin a chuté (42 % à 27 %), celle d’épinette–sapin s’est maintenue (12 % à 11 %) et celle mixte a augmenté (32 % à 52 %). La vulnérabilité des forêts a été estimé à partir des réductions de volume résineux suivant des simulations d’épidémies de différentes sévérité (faible, modérée et sévère) et effet des feuillus sur la réduction de la défoliation des hôtes. Les pertes de bois des épidémies débutant en 1985 ou 2004 se sont avérées similaires et s’élevaient de 15 %–46 % (aucun effet des feuillus) à 13 %–39 % (effet des feuillus maximal) pour les épidémies légères et sévères. Étant donné la difficulté d’augmenter l’abondance d’épinettes et les pertes nettes de production résineuse liées au contenu élevé en feuillus, nous remettons en question les bénéfices liés à la préservation des feuillus et recommandons une utilisation accrue du contrôle de la végétation en plantation pour augmenter l’abondance d’épinette.
Deepa Pureswaran, Louis De Grandpré, Anthony Taylor, David Paré, Martin Barrette, Jacques Régnière, Hubert Morin, Daniel Kneeshaw. Climate-induced changes in host tree-insect phenology may drive ecological state-shift in boreal forest. 2015. Ecology 96(6):1480-1491
DOI : 10.1890/13-2366.1
Climate change is altering insect disturbance regimes via temperature-mediated phenological changes and trophic interactions among host trees, herbivorous insects and their natural enemies in boreal forests. Range expansion and increase in outbreak severity of forest insects are occurring in Europe and North America. The degree to which northern forest ecosystems are resilient to novel disturbance regimes will have direct consequences on the provisioning of goods and services from these forests and on long-term forest management planning. Among major ecological disturbance agents in the boreal forests of North America is a tortricid moth, the eastern spruce budworm, which defoliates fir (Abies spp.) and spruce (Picea spp.). Northern expansion of this defoliator in eastern North America and climate-induced narrowing of the phenological mismatch between the insect and its secondary host, black spruce (Picea mariana), may permit greater defoliation and mortality in extensive northern black spruce forests. While spruce budworm outbreak centres have appeared in the boreal black spruce zone historically, defoliation and mortality were minor. Potential increases in outbreak severity and tree mortality raise concerns about the future state of this northern ecosystem. Severe spruce budworm outbreaks could decrease stand productivity compared with their occurrence in more diverse, southern balsam fir forest landscapes that have coevolved with outbreaks. Furthermore, depending on the proportion of balsam fir and deciduous species present and fire recurrence, changes in regeneration patterns and in nutrient cycling could alter ecosystem dynamics and replace black spruce by more productive mixed-wood forest, or by less productive ericaceous shrublands. Long-term monitoring, manipulative experiments and process modeling of climate-induced phenological changes on herbivorous insect pests, their host tree species and natural enemies in northern forests are therefore crucial to predicting species range shifts and assessing ecological and economic impacts.
Gerardo Reyes, Daniel Kneeshaw. Ecological Resilience: Is It Ready for Operationalisation in Forest
Management? 2014. Advances in Environmental Research. chap 32:195-212
Given the physiographic variability, variation in socio-political landscapes, and differences in connectedness of people and communities associated with boreal forest ecosystems, approaches to forest management that are flexible enough to accommodate this variation are needed. Moreover, to ensure sustainable forest resource use, we need to embrace the inherent complexity of boreal forest ecosystems rather than eliminate it, and be prepared to adapt and adjust as environmental conditions change. While ecological resilience may be a useful forest management objective to this end, developing general guidelines to integrate it into practice remains elusive. We address a number of questions often posed by managers when attempting to include ecological resilience into forest management planning. Our goal is to determine if the theoretical foundation of ecological resilience is sufficiently developed to provide a general framework that can be applied for boreal forest management.
Benoît St-Onge, Jean-François Sénécal, Udayalaksmi Vepakoma, Frédérick Doyon, Daniel Kneeshaw. Canopy Gap Detection and Analysis with Airborne Laser Scanning. 2014. Forestry Applications of Airborne Laser Scanning 27:419-437
DOI : 10.1007/978-94-017-8663-8_21
The opening and closure of “gaps” in forest canopies plays an important role in the structure, turnover, and overall ecological processes of natural forests. Gap characterization was until recently mostly based on field studies and relied on sampling approaches. ALS (Airborne Laser Scanning) has now revolutionized this field of scientific enquiry by giving researchers the capacity to detect and measure gaps rapidly over large areas. We first provide a brief scientific background on gaps and then succinctly review field and other conventional remote sensing methods to characterize them. We then turn our attention to the principles of ALS-based gap detection and review different methods of automated gap delineation and measurement. We explain how gap types can be automatically classified, and how multitemporal ALS can be used to not only monitor gap dynamics, but also to reveal the complex role of gaps in influencing tree growth within and around them.
Xiongqing Zhang, Yuancai Lei, Zhihai Ma, Changhui Peng, Daniel Kneeshaw. Insect-induced tree mortality of boreal forests in eastern Canada under a changing climate. 2014. Ecology and Evolution 4(12):2384-2394
DOI : 10.1002/ece3.988
Forest insects are major disturbances that induce tree mortality in eastern coniferous (or fir-spruce) forests in eastern North America. The spruce budworm (SBW) (Choristoneura fumiferana [Clemens]) is the most devastating insect causing tree mortality. However, the relative importance of insect-caused mortality versus tree mortality caused by other agents and how this relationship will change with climate change is not known. Based on permanent sample plots across eastern Canada, we combined a logistic model with a negative model to estimate tree mortality. The results showed that tree mortality increased mainly due to forest insects. The mean difference in annual tree mortality between plots disturbed by insects and those without insect disturbance was 0.0680 per year (P < 0.0001, T-test), and the carbon sink loss was about 2.87t C ha?1 year?1 larger than in natural forests. We also found that annual tree mortality increased significantly with the annual climate moisture index (CMI) and decreased significantly with annual minimum temperature (Tmin), annual mean temperature (Tmean) and the number of degree days below 0°C (DD0), which was inconsistent with previous studies (Adams et al. 2009; van Mantgem et al. 2009; Allen et al. 2010). Furthermore, the results for the trends in the magnitude of forest insect outbreaks were consistent with those of climate factors for annual tree mortality. Our results demonstrate that forest insects are the dominant cause of the tree mortality in eastern Canada but that tree mortality induced by insect outbreaks will decrease in eastern Canada under warming climate.
Gauthier Ligot, Philippe Balandier, Benoit Courbaud, Mathieu Jonard, Hugues Claessens, Daniel Kneeshaw. Managing understory light to maintain a mixture of species with different shade tolerance. 2014. For. Ecol. Manage. 327:189-200
DOI : 10.1016/j.foreco.2014.05.010
Close-to-nature management of forests has been increasingly advocated. However forest managers often face difficulties in maintaining mixtures of species with different shade tolerance. In uneven aged stand management, understory light can be manipulated by modifying stand structure and composition, in addition to stand density. Using a forest radiative transfer model, we analyzed how different cutting strategies could modify light availability under the post-harvest canopy. To calibrate the model, we measured and mapped trees in 27 plots with structures ranging from secondary-successional oak forests to late-successional beech forests. We measured understory light and crown openness and verified that our forest radiative transfer model well captured the variability of understory light among the studied stands (R2=87%). We then compared cutting strategies varying in type and intensity and provided indications to promote the regeneration of mixtures of species of different shade tolerances. In particular, creating gaps of about 500m2 provided adequate light for small regeneration clumps. Cutting from below, species-specific cutting and uniform cutting were also appropriate for tree regeneration but uniform cutting required higher harvest intensity. Cutting from above slightly increased understory light and promoted more shade tolerant species. © 2014 Elsevier B.V.
Charles Nock, Olivier Taugourdeau, Christian Messier, Daniel Kneeshaw, Timothy Work. Urban forests on the front line. 2014. Science 343(6168):249
DOI : 10.1126/science.343.6168.249-a
In their Review “The consequence of tree pests and diseases for ecosystem services” (15 November 2013, p. 823), I. L. Boyd et al. discuss the effects of pests on forest ecosystem services. However, urban forests garnered little attention.
With increasing global trade, urban trees are among the first affected by newly introduced pests. Low tree diversity combined with low tree density in cities limits the potential for compensatory responses of ecosystems, unlike the model presented by Boyd et al. Decades ago, diseased elms were felled en masse in cities in eastern North America; many of the same cities are bracing yet again for extensive canopy loss, this time due to emerald ash borer (1). Boyd et al. suggest that cultural services are affected, but a more complete portfolio includes services important to city dwellers, such as air pollution removal and climate regulation (2, 3).
As Boyd et al. suggest, planting more species and species selection will reduce losses to new tree pests. However, few species tolerate urban conditions, leading to overuse of those that do. Greater genetic diversity within species is particularly important to address enhanced pest risks in urban areas (4). Chemical treatments of urban trees can prolong their service life while also controlling pest spread (1). Outbreak-related tree removals cost millions. A greater investment in better infrastructure and soil [e.g., (5)] would be a cost-effective way to reduce stress and permit more species to be planted.
Luana Graham-Sauvé, Christian Messier, Daniel Kneeshaw, Timothy Work. Shelterwood and multicohort management have similar initial effects on ground beetle assemblages in boreal forests. 2013. For. Ecol. Manage. 306:266-274
DOI : 10.1016/j.foreco.2013.06.019
Partial cutting has been proposed as a means to better conserve biodiversity in managed forest landscapes. However, partial cutting encompasses many forms of silviculture; some with implicit goals of maintaining biodiversity such as multicohort harvesting or others which may specifically focus on regeneration of stands but may still provide some additional benefits for biodiversity such as shelterwood harvesting. Here we compared ground beetle assemblages of clear cuts, shelterwoods, multicohort harvested stands and uncut stands collected using pitfall traps both 2 and 3-years post-harvest. We hypothesized that partial cutting treatments would maintain assemblages that were more similar to uncut stands than to clear cuts. We further hypothesized that among partial cuts the multicohort harvested stands, with relatively high levels of retention (66%), would maintain beetle assemblages that were more similar to uncut stands than would shelterwoods, which had lower levels of retention (50%). We collected 6692 individuals, representing 42 species. Catch rates of beetles were similar among all harvested treatments (shelterwood, multicohort and clear cuts) and lower than uncut stands. Species richness and composition was similar between shelterwood and multicohort stands. Both partial cut treatments fell between clear cuts and uncut stands in terms of species richness and compositional similarity. Compositional differences between uncut stands and partial cut stands were defined primarily by reduced abundances of forest associated species such as Agonum retractum (LeConte), Synuchus impunctatus (Say) and four Pterostichus species within partial cuts. Within partial cuts, beetle assemblages differed between machine corridors with 0% retention and adjacent partial cut strips (50% retention) and uncut vegetation corridors (100%). We conclude that both shelterwoods and multicohort harvesting stands provide at least initially similar benefits for biodiversity compared to clear cutting although neither maintains assemblages consistent with those found in uncut stands. We expect that these similarities will end once trees are removed from shelterwoods. The reductions in abundances within partial cuts may extend the time necessary for individual populations to increase to pre-harvest levels in partial cuts. For land-managers, similar initial responses of beetle assemblages in multicohort and shelterwood harvests may permit some flexibility for conservation planning whereby final removal of seed trees within shelterwoods could be delayed depending on the status of recovering beetle populations.
Gerardo Reyes, Louis De Grandpré, Daniel Kneeshaw. The Relative Importance of Natural Disturbances and Local Site Factors on Woody Vegetation Regeneration Diversity across a Large, Contiguous Forest Region. 2013. Open Journal of Forestry 3(3):88-98
DOI : 10.4236/ojf.2013.33015
Stand-level diversity after natural disturbance can potentially differ across a large, contiguous forest region despite being dominated by the same canopy species throughout as differences in disturbance types and local site conditions can regulate species distribution. Our main objective was to examine the relative importance of natural disturbances (spruce budworm (Choristoneura fumiferana) outbreak, windthrow, and their interaction) and local site factors (climate, physiography, and stand structure and composition variables) on woody vegetation diversity among three, physiographically distinct locations across a large, contiguous forest region. Seventy-six Abies balsamea-Betula spp. stands affected by natural disturbance were compared and analysed using canonical ordination methods, diversity indices, and ANOVA. Different combinations of factors were important for vegetation re-establishment at each location. Differences in alpha, beta, gamma, Shannon’s H’, and evenness (J) diversity indices were observed among locations across the study region. Our findings indicate that while certain processes are important for maintaining canopy dominance by Abies balsamea and Betula spp. throughout the region, different combinations of factors were important for creating variation in woody species diversity among locations that resulted in greater woody species diversity at the regional scale.
Isabelle Witté, Daniel Kneeshaw, Christian Messier. Do partial cuts create forest complexity? A new approach to measuring the complexity of forest patterns using photographs and the mean information gain. 2013. For. Chron. 89(3):340-349
DOI : 10.5558/tfc2013-064
L’aménagement forestier contribue à simplifier la structure et la composition forestière. En conséquence, le maintien de la complexité structurelle est de plus en plus cité comme objectif de l’aménagement durable des forêts. Différentes initiatives proposent d’utiliser les coupes partielles de manière à augmenter la complexité des forêts. En utilisant la longueur de la description des patrons forestiers comme un nouvel indicateur de complexité des forêts, nous avons comparé les effets de deux intensités de coupes partielles sur la complexité des patrons forestiers, aux complexités mesurées dans des forêts fermées. Nos résultats montrent que les coupes partielles permettent d’augmenter la complexité des patrons forestiers par rapport aux forêts matures et secondaires.
Ekaterina Shorohova, Timo Kuuluvainen, Sylvie Gauthier, Daniel Kneeshaw. Variability and dynamics of old-growth forests in the circumboreal zone: implications for conservation, restoration and management. 2012. Silva Fennica 45(5):785-806
Due to the unprecedented loss of old-growth forests to harvesting throughout circumboreal regions an understanding of similarities and differences in old-growth dynamics is needed to design effective restoration, management and conservation efforts. This paper reviews concepts, prevalence and variability of old-growth forests across landscapes, and evaluates different stand scale dynamics at the old-growth stage across the circumboreal zone. Old-growth historically dominated many boreal forest landscapes in both Eurasia and North America. Throughout much of North America, and to some extent in western Siberia, the natural prevalence and development of old-growth forests are regulated by the occurrence of stand-replacing fires. In eastern North America and Siberia, insect outbreaks may, however, be more important. Insect outbreaks as well as recurrent non-stand replacing surface fires and windthrows, when occurring at the old-growth stage, often form stands characterized by several tree age-class cohorts. This multi age-class forest development type is common in Europe and eastern Siberia but its prevalence and importance in boreal North-America is not well documented. Similarities in successional dynamics across the circumboreal region are found in the development of mono-dominant even-aged stands, the replacement of shade intolerant tree species by shade tolerant species, as well as in all-aged stands driven by small-scale gap dynamics. The message to land managers is that the focus should not only be on setting aside remaining old-growth forests or in restoring static old-growth attributes, but also in emulating natural disturbances and successional dynamics at landscape and regional scales to maintain natural variability in old-growth attributes through time.
Yves Bergeron, Timo Kuuluvainen, Daniel Kneeshaw. Forest Ecosystem Structure and Disturbance Dynamics across the Circumboreal Forest. 2011. The Sage Handbook of Biogeography. 14:261-278
Francis Manka, Daniel Kneeshaw, Brian Harvey. Chablis au Témiscamingue 2006 : une évaluation des espèces qui ont succombé et des espèces qui ont été recrutées. 2011. Chaire industrielle CRSNG UQAT-UQAM-AFD. Note de recherche 26. 4 p.
Le 17 juillet 2006, des vents d’une très grande force ont causé un chablis allant du sud du Témiscamingue jusqu’en Mauricie, soit plus de 21 000 ha de forêt renversée. Ce chablis a offert une occasion unique d’étudier les effets sur la composition et la structure forestière que peut avoir cette perturbation méconnue de la zone tem-pérée nordique. Nous avons donc mis en place cette étude afin d’évaluer : 1) l’importance des traits fonctionnels des espèces sur la vulnérabilité d’un arbre à céder sous la force du vent selon que le chablis est sévère ou modéré, et 2) l’utilisation des microsites post-chablis dans le recrutement des espèces arborescentes. En som-me, nous avons observé que les arbres sont plus vulnérables au chablis sévère lorsqu’ils sont résineux et/ou intolérant à l’ombre, et/ou lorsqu’ils ont un DHP supérieur à 20 cm et/ou des racines superficielles, tandis que les arbres intolérants à l’ombre et/ou résineux sont plus facilement affectés par le chablis modéré. De toutes les es-pèces, le peuplier à grandes dents est la plus vulnérable aux chablis sévères et modérés. Les probabilités de se déraciner plutôt que de casser sous un chablis sévère augmentent en fonction du DHP. Finalement, les microsi-tes de puits et de monticules créés lors d’un déracinement ne semblent pas jouer un rôle déterminant dans le recrutement des espèces, à l’exception du bouleau jaune. En conclusion, les chablis ont une tendance à faire accélérer le processus de succession ainsi qu'à faire augmenter l’abondance de bouleau jaune.
Benoît Gendreau-Berthiaume, Brian Harvey, Daniel Kneeshaw. La coupe de succession et la coupe avec protectiondes petites tiges marchandes se rapprochent-elles des perturbations naturelles partielles ? 2011. Chaire industrielle CRSNG UQAT-UQAM-AFD. Note de recherche 27. 4 p.
L’objectif de cette recherche, réalisée en forêt mélangée au Témiscamingue, était de comparer une forêt dynami-sée par des perturbations naturelles partielles avec deux types de coupe partielle : une coupe de succession (CS) et une coupe avec protection des petites tiges marchandes (CPPTM). Les aspects suivants étaient étudiés : 1) la diversité structurelle des peuplements résiduels; 2) la croissance des arbres résiduels; 3) la composition de la régénération et 4) la croissance des gaules de sapin baumier. Les résultats démontrent que la CS et la CPPTM maintiennent une diversité structurelle et une densité d’espèces tolérantes à l’ombre semblables à celles que nous avons mesurées en forêt naturelle partiellement perturbée. À la suite de la CS et de la CPPTM, les es-pèces étudiées, à l’exception de l’épinette noire, avaient un accroissement radial important, et même supérieur à celui mesuré en forêt naturelle. En conclusion, les deux traitements sylvicoles évalués présentent un intérêt po-tentiel pour l’industrie forestière, car ces deux coupes permettent de maintenir une diversité structurelle et une composition en espèces qui équivalent à celles de la forêt dynamisée par des perturbations naturelles partielles.
Marilou Beaudet, Julie Poulin, Yves Bergeron, David Coates, Daniel Kneeshaw, Suzanne Brais, Brian Harvey, Christian Messier. Gestion des conditions lumineuses générées par la coupe partielle en variant l’intensité et le patron spatial de récolte : UNE APPROCHE DE MODÉLISATION. 2011. Chaire industrielle CRSNG UQAT-UQAM-AFD. Note de recherche 25. 4 p.
Les conditions lumineuses jouent un rôle important dans la dynamique forestière et sont directement affectée par les interventions sylvicoles. L'objectif de cette étude était de déterminer comment les conditions lumineuses du sous-bois d'un peuplement boréal mixte sont affectées par des variations dans l'intensité et le patron spatial de récolte. À l'aide du modèle de simulation SORTIE-ND, nous avons simulé neuf traitements de coupe partielle en combinant trois taux de prélèvement (30 %, 45 % et 60 % de la surface terrière) et trois patrons de récolte (uniforme, par bandes étroites et par trouées). Nos résultats démontrent que la récolte n'augmente pas nécessai-rement la transmission de la lumière en sous-étage d'une façon proportionnelle au taux de prélèvement, le patron spatial de récolte jouant un rôle déterminant. De façon générale, on observe que, pour un même niveau de prélè-vement, un patron de récolte plus agrégé génère des conditions lumineuses plus élevées.
Lionel Humbert, Daniel Kneeshaw. Identifying insect outbreaks: a comparison of a blind-source separation method with host vs non-host analyses. 2011. Forestry
DOI : 10.1093/forestry/cpr047
The identification of past insect outbreaks is often determined using a comparison of host/non-host tree ring growth chronologies. Yet this may be a problem when non-hosts are either affected by the outbreaking insect or when the growth of host and non-host trees does not respond similarly to the same climatic factors. We investigate the use of a blind source separation method to identify past outbreaks. This method, used in neurology and called independent components analysis (ICA), directly identifies disturbance patterns. We analysed the tree-ring data from papers dealing with insect outbreaks. These papers focus on western spruce budworm, pandora moth and Douglas-fir tussock moth outbreaks. We compared the results of the original analyses, conducted using the host/non-host approach, with results from ICA. We detected the outbreaks identified in the original papers. However, the start and end dates for the outbreaks were different in 75 per cent of the ICA analyses. On the other hand, we were able to detect growth reduction in non-host Ponderosa pine chronologies as well as increased growth during outbreak periods. Since conventional methods may be less robust when the growth of non-host trees is affected, the ICA may provide a powerful new method to identify outbreaks in such situation.
Marilou Beaudet, Julie Poulin, David Coates, Yves Bergeron, Daniel Kneeshaw, Suzanne Brais, Christian Messier, Brian Harvey. Managing understory light conditions in boreal mixedwoods through variation in the intensity and spatial pattern of harvest: A modelling approach. 2010. For. Ecol. Manage. 261(1):84-94
DOI : 10.1016/j.foreco.2010.09.033
In the context of partial harvesting, adequately managing post-harvest light conditions are essential to obtain a desired composition of tree species regeneration. The objective of this study was to determine how varying the intensity and spatial pattern of harvest would affect understory light conditions in boreal mixedwood stands of northwestern Quebec using the spatially explicit SORTIE-ND light model. The model was evaluated based on comparisons of observed and predicted light levels in both mapped and un-mapped plots. In mapped plots, reasonably accurate predictions of the overall variation in light levels were obtained, but predictions tended to lack spatial precision. In un-mapped plots, SORTIE-ND accurately predicted stand-level mean GLI (Gap Light Index) under a range of harvest intensities. The model was then used to simulate nine silvicultural treatments based on combinations of three intensities of overstory removal (30%, 45% and 60% of basal area) and three harvest patterns (uniform, narrow strips, large gaps). Simulations showed that increasing overstory removal had less impact on light conditions with uniform harvests, and a more marked effect with more aggregated harvest patterns. Whatever the harvest intensity, uniform cuts almost never created high light conditions (GLI > 50%). Gap cuts, on the other hand, resulted in up to 40% of microsites receiving GLI > 50%. Our results suggest that either a 30% strip or gap cut or a 45–60% uniform partial harvest could be used to accelerate the transition from an aspen dominated composition to a mixedwood stand because both types of cut generate the greatest proportion of moderately low light levels (e.g., 15–40% GLI). These light levels tend to favour an accelerated growth response among shade-tolerant conifers, while preventing excessive recruitment of shade-intolerant species. A better understanding of how spatial patterns of harvest interact with tree removal intensity to affect understory light conditions can provide opportunities for designing silvicultural prescriptions that are tailored to species’ traits and better suited to meet a variety of management objectives.
Udayalaksmi Vepakoma, Benoît St-Onge, Daniel Kneeshaw. Interactions of multiple disturbances in shaping boreal forest dynamics: a spatially explicit analysis using multi-temporal lidar data and high-resolution imagery. 2010. Journal of Ecology 98(3):526-539
DOI : 10.1111/j.1365-2745.2010.01643.x
- Mixed-wood boreal forests are often considered to undergo directional succession from shade-intolerant to shade-tolerant species. It is thus expected that overstorey gaps should lead to the recruitment of shade-tolerant conifers into the canopy in all stand development stages and that the recruitment of shade-intolerant hardwoods would be minimal except in the largest gaps.
- We analysed short-term gap dynamics over a large 6-km2 spatial area of mixed-wood boreal forest across a gradient of stands in different developmental stages with different times of origin since fire (expressed as stand 'age') that were affected differentially by the last spruce budworm (SBW) outbreak. Structural measurements of the canopy from lidar data were combined with spectral classification of broad species groups to characterize the gap disturbance regime and to evaluate the effect of gap openings on forest dynamics.
- Estimated annual gap opening rates increased from 0.16% for 84-year-old stands to 0.88% for 248-year-old stands. Trees on gap peripheries in all stands were more vulnerable to mortality than interior canopy trees.
- Due to recovery from the last SBW outbreak 16 years previously, gap closure rates were higher than opening rates, ranging from 0.44% to 2.05% annually, but did not show any relationship with stand age. There was, however, a continuing legacy of the last SBW outbreak in old-conifer stands in terms of a continued high mortality of conifers. In all stands, the majority of the openings were filled from below, although a smaller but significant proportion filled from lateral growth of gap edge trees.
- Synthesis. The forest response to moderate- to small-scale disturbances in old-growth boreal forest counters the earlier assumption that the transition from one forest state to the next is slow and directional with time since the last fire. Overall, a small 6% increase in hardwoods was observed over 5 years, largely due to regeneration in-filling of hardwoods in gaps instead of successional transition to more shade-tolerant conifers. Gaps are vital for hardwood maintenance while transition to softwoods can occur without perceived gap-formation as overstorey trees die, releasing understorey trees.
Yves Bergeron, Annick St-Denis, Daniel Kneeshaw. The role of gaps and tree regeneration in the transition from dense to open black
spruce stands. 2010. For. Ecol. Manage. 259(3):469-476
DOI : 10.1016/j.foreco.2009.11.002
Black spruce forests growing on clay soils in northwestern Quebec change structure from dense even-aged stands to open uneven-aged stands such that almost all forests older than 200 years have an open canopy. These forests become unproductive over time because they are prone to paludification. The main goal of our study was to document the transition between dense and open stands in terms of gap dynamics, with a focus on tree regeneration. Our objective was to determine whether forests remain open due to a lack of regeneration, a lack of growth or both. Nine stands along a 50–250-year-old time since fire gradient were sampled with the line intersect sampling method. Gap fraction increased with stand age and reached a maximum of 77% in the oldest site. In old-growth stands, gaps were interconnected due to the low density of these forests. Most of the gap makers were found with broken stems. Regeneration was dominated by black spruce layers and was relatively abundant (1.71 stems/m2). However, the majority of gap fillers were smaller than 1 m in height in stands of all ages. Instead of a lack of regeneration, the opening of the forests is due to a lack of growth associated with cold and wet organic deposits. Partial harvesting could be implemented on the most productive sites, while management techniques including soil disturbances will be required on low productivity sites to recreate good growth conditions.
Pascal Côté, Rebecca Tittler, Andrew Fall, Marie-Josée Fortin, Daniel Kneeshaw, Christian Messier. Comparing different forest zoning options for landscape-scale management of the boreal forest: Possible benefits of the TRIAD . 2010. For. Ecol. Manage.
DOI : 10.1016/j.foreco.2009.10.038
Forest management has been criticised in the last 20 years for its negative impact on the native species, structures and functions of the forest. Of many possible alternatives proposed to minimize these effects, the functional zoning (or TRIAD) approach is gaining popularity in North America. The goal of this approach is to minimize the negative environmental impacts of forestry while maintain timber supply by dividing the forest into three broad land-use zones: (1) conservation, (2) ecosystem management, and (3) wood production. In this study, we used a spatially explicit landscape model to simulate the effects of fire and six different forest management scenarios on a boreal mixedwood forest management unit in central Quebec. The management scenarios examined included the current practices scenario, a scenario proposed by the provincial government, and four TRIAD scenarios varying in the amount of forest allocated to each of the three zones. For each scenario, we examined the harvest volume, percentage old-growth forest or old forest managed to favour old-growth attributes, and effective mesh size of forest patches by 20-year age classes. With more area set aside for conservation and high-retention partial cut harvesting techniques designed to maintain the attributes of old-growth stands, all TRIAD scenarios resulted in higher percentages of stands with old-growth attributes than the current practices scenario and the government proposed scenario, and two of the four TRIAD scenarios also resulted in higher harvest volume over the long term. All forest management scenarios resulted in significantly lower effective mesh size than the fire-only scenario, but this difference was not as pronounced for the four TRIAD scenarios as for the current practice and government proposed scenarios. We conclude that the TRIAD approach has the potential to minimize some of the negative impacts of forestry on the landscape, while maintaining timber supply over the long term.
Benoît Gendreau-Berthiaume, Daniel Kneeshaw. Influence of Gap Size and Position within Gaps on Light Levels. 2009. International Journal of Forestry Research Article ID 581412, 8 pages
DOI : 10.1155/2009/581412
The previous studies have reported maximum light levels at different positions within gaps but many of these studies are based on gaps of different size. The objective of this study is to evaluate the influence of gap size and position within gap on light distribution in gaps and under the canopy north of gaps in a mixedwood temperate forest. For three gap sizes, with gap widths ranging between 0.5 and 1.5 times the height of the surrounding stand, light was measured at different positions along the north-south axis in each gap using two different techniques (hemispherical photographs and instantaneous measurements). In small gaps, the position with the most light was close to the northern edge although not under the canopy north of the gap. For both methods, the position with the highest light level shifted from the north towards the center of gaps as gap size increased which clarifies some of the variability in light measurements previously observed in gap studies. Higher light levels in the northern part of small and medium gaps compared to the southern portion could allow management of a mixture of species with intolerant species in the northern portions of gaps and tolerant species to the south.
Marie-Noël Caron, Heikki Kauhanen, Timo Kuuluvainen, Daniel Kneeshaw, Louis De Grandpré. Canopy gap characteristics and disturbance dynamics in old-growth Picea abies stands in northern Fennoscandia: Is the forest in quasi-equilibrium? 2009. Ann.Bot.Fennici 46:251-262
Emulating natural disturbances in managed forests has been suggested as a potential solution to maintain habitat conditions similar to those observed in old-growth forests. We examined the gap attributes and disturbance history of old-growth Picea abies-dominated stands in the northern boreal vegetation zone of the Pallas-Yllästunturi National Park in northwestern Finland to evaluate the influence of gaps on forest dynamics and the temporal patterns of gap creation. Six stands located at two sites were sampled along 400-m-long linear transects so that all intersected gaps were measured and dated. The average proportion of the forest area in the gaps was 43.1% ± 7.5%. An average gap size was estimated to be 221 m2 ± 198 m2, whereas the median gap size was 170.2 m2. While only 20% of the gaps were smaller than 100 m2, nearly 85% of them were smaller than 300 m2. Gap creation was constant with no distinct peaks from 1965 to 2005. Thus, forest dynamics were driven by continuous small-scale disturbances and were characterized by quasi-equilibrium structure. However, the results of the growth release analysis indicated that more severe disturbance(s) may have occurred almost two centuries ago. Emulating this type of forest dynamics would imply selective or group harvesting of trees as the predominant methods, but larger-scale, more intensive cuttings could also be carried out periodically.
Rebecca Tittler, Nancy Gélinas, Alain Paquette, Kati Berninger, Héloise Rheault, Philippe Meek, Nadyre Beaulieu, Daniel Kneeshaw, Christian Messier. TRIAD zoning in Quebec: Experiences and results after 5 years. 2009. For. Chron. 85(6):885-896
The TRIAD approach to forest management involves dividing the forest into 3 zones, each with its own management objectives, but with the overall goal of increasing the ecological and economic sustainability of the forest. For the past 5 years, we have been experimenting with TRIAD zoning in central Quebec, incorporating social interests into the original concept of TRIAD management. Results generally indicate that this approach is economically viable, socially acceptable, and preferable ecologically in this area. Although much remains to be done, thus far the consensus among the various project participants is that this approach may be a good fit for the public forest of Canada.
Dans le cadre d’un aménagement forestier TRIADE, la forêt est divisée en trois zones ayant chacune ses propres objectifs d’aménagement. L’objectif global est cependant toujours l’atteinte d’une gestion durable au niveau écologique et économique. Depuis 5 ans, nous expérimentons avec le concept de zonage TRIADE au centre du Québec, incorporant les intérêts sociaux dans le concept original de la TRIADE. Nos résultats indiquent que cette approche est viable au niveau économique, acceptable au niveau social et préférable au niveau écologique. Il nous reste beaucoup à faire, mais le consensus général des nombreux participants est que cette approche pourrait nous aider à mieux gérer les forêts publiques du Canada.
Udayalaksmi Vepakoma, Benoît St-Onge, Daniel Kneeshaw. Height growth of regeneration in boreal forest canopy gaps – does the type of gap matter? An assessment with lidar time series. 2008. SilviLaser 2008, Sept. 17-19, 2008 – Edinburgh, UK 9 p.
Large canopy gaps in old-growth forests, formed as a result of tree fall events over time, could be composed of regeneration in various stages of growth different from that of single mortality events. Though important to understand forest dynamics such complex processes are rarely monitored due to limited techniques. Applying object-based techniques on a series of three lidar datasets acquired over nine years in boreal forests, we characterised gap events into old gaps, gap expansions and new random gaps. Combining broad species class from high resolution images, and individually locating gap saplings on the lidar surface, specieswise height growth across gradients of height was estimated. The results indicate distinct height growth patterns of both hardwood and softwood gap saplings in different gap events. The methods can potentially be extended to develop accurate juvenile growth patterns.
Udayalaksmi Vepakoma, Benoît St-Onge, Daniel Kneeshaw. Spatially explicit characterization of boreal forest gap dynamics using multi-temporal lidar data. 2008. Remote Sensing of Environment 112(5):2326-2340
Understanding a disturbance regime such as gap dynamics requires that we study its spatial and temporal characteristics. However, it is still difficult to observe and measure canopy gaps extensively in both space and time using field measurements or bi-dimensional remote sensing images, particularly in open and patchy boreal forests. In this study, we investigated the feasibility of using small footprint lidar to map boreal canopy gaps of sizes ranging from a few square meters to several hectares. Two co-registered canopy height models (CHMs) of optimal resolution were created from lidar datasets acquired respectively in 1998 and 2003. Canopy gaps were automatically delineated using an object-based technique with an accuracy of 96%. Further, combinatorics was applied on the two CHMs and the delineated gaps to provide information on the area of old and new gaps, gap expansions, new random gap openings, gap closure due to lateral growth of adjacent vegetation or due to vertical growth of regeneration. The results obtained establish lidar as an excellent tool for rapidly acquiring detailed and spatially extensive short-term dynamics of canopy gaps. © 2007 Elsevier Inc. All rights reserved.
Gerardo Reyes, Daniel Kneeshaw. Moderate-severity disturbance dynamics in Abies balsamea- Betula spp. forests: the relative importance of disturbance type and local stand and site characteristics on woody vegetation response. 2008. Ecoscience 15:241-249
Marie-Christine Adam, Daniel Kneeshaw. Local level criteria and indicator frameworks: A tool used to assess aboriginal forest ecosystem values. 2008. For. Ecol. Manage. 255(7):2024-2037
DOI : 10.1016/j.foreco.2007.12.051
Although the importance of aboriginal knowledge, values and perspectives in sustainable development has been recognised for many decades, worldwide examples exist showing that aboriginal involvement is less then effective. How and where to include aboriginal needs and goals has however been problematic. Ultimately, aboriginal forest values need to be considered with scientific strategies and their role and compatibility with forest conditions needs to be explored. Criteria and indicator (C&I) frameworks can be used as a platform to include community needs and goals in management decisions. This review compares aboriginal forest ecological perspectives defined by Canadian local level C&I frameworks with non-aboriginal local level C&I frameworks to identify their differences at the indicator level. Three major themes mark the differences between aboriginal and non-aboriginal indicators: (1) aboriginal frameworks introduce ecological indicators of cultural importance; (2) there is an aesthetic concern for forest operations especially if they affect cultural owners; and (3) indicators regarding the access to resources are more complex and include the sustainability of the productivity, proximity, integrity and quality of resources used in traditional activities. Results show that First Nation forest sustainability issues are in effect a combination of forest conditions and values. Inclusion of forest values in C&I frameworks is necessary because: (1) aboriginal communities do not dissociate culture from the environment and thus forest values from forest condition, (2) they have an impact on resulting forest management strategies and decisions, and (3) they offer a holistic approach to sustainability issues and a better picture of local environmental contexts.
Mathieu Bouchard, Yves Bergeron, Daniel Kneeshaw. Ecosystem management based on large-scale disturbance pulses: A case study from sub-boreal forests of western Quebec (Canada). 2008. For. Ecol. Manage. 256(10):1734-1742.
DOI : 10.1016/j.foreco.2008.05.044
The northern Témiscamingue region (western Québec) sustained regional-scale pulses of natural disturbances during the 1850–2000 period, such as severe fires during the 1908–1926 period, two severe spruce budworm outbreaks that occurred in 1909–1918 and 1974–1984, and two birch dieback episodes around 1940 and 1980. These disturbances produced synchronous fluctuations in forest characteristics over large spatial scales. In this paper, we review possible responses of flora and fauna to pulsed large-scale disturbance events and speculate on whether they should be emulated to reduce the impacts of forest management on non-timber resources. The importance of large-scale disturbance pulses for biodiversity and forest ecosystem integrity is potentially great, but this aspect has been poorly investigated by previous research, and thus there is little information available to guide forest management. Large-scale, synchronous disturbances could be emulated by clustering harvesting activities in time, for example by creating “harvest pulses” of 10–20 years, separated by periods of 50–100 years or so with low harvest rates. A potential disadvantage of this strategy is that when our capacity to predict future natural disturbances is low, there is a higher probability of accidentally taking the forest ecosystem outside of the range of natural variability compared with a status quo forest management scenario. From a socio-economic perspective, another potential disadvantage is in creating irregular wood flows to the forest transformation industry. Nonetheless, in a context where the forest has been over-disturbed in the recent past, a forest management strategy involving fluctuating harvest rates could provide the means for faster ecosystem recovery compared with a status quo strategy. We recommend that the potential importance of disturbance pulses for boreal and sub-boreal ecosystems be more thoroughly investigated by future research to inform management and conservation policies. © Elsevier B.V. All rights reserved.
Yves Bergeron, Eve Lauzon, Daniel Kneeshaw. Reconstruction of fire history (1680-2003) in Gaspesian mixedwood boreal forests of eastern Canada. 2007. For. Ecol. Manage. 244(1-3):41-49
DOI : 10.1016/j.foreco.2007.03.064
Marcel Prévost, Daniel Kneeshaw. Natural canopy gap disturbances and their role in maintaining mixed-species forests of central Quebec, Canada. 2007. Can. J. For. Res. 37(9): 1534–1544.
DOI : 10.1139/X07-112
Until recently, natural dynamics of mixedwood stands have been largely ignored, resulting in the transformation of many North American mixedwoods into conifer- or hardwood-dominated stand types. The goal of this study was to examine canopy gap dynamics in balsam fir (Abies balsamea (L.) Mill.) – yellow birch (Betula alleghaniensis Britt.) mixedwoods to better understand possible mechanisms for species coexistence. Gap proportion in 12 study stands varied between 9% and 30% of the total stand area, while gap size varied from 20 to 2100 m². Balsam fir mortality was the primary cause of gap formation. Balsam fir and mountain maple (Acer spicatum Lamb.) dominated the tree and shrub regeneration layers, respectively. Shrub competition slows the natural filling of gaps by tree species. Our results indicate that yellow birch is most abundant in gaps over 800 m² and balsam fir in those under 200 m². Transition models showed that the greater longevity of yellow birch than balsam fir ensured its maintenance as a dominant. Dominant species coexistence thus results from divergent use of available resources through time and space. Forest management should maintain variability in harvest timing and size because the use of one gap size or a single rotation age will lead to an imbalance in species proportion relative to natural stands. © 2007 NRC Canada.
Jusqu’à récemment, la dynamique naturelle des peuplements mixtes a été largement ignorée, ce qui a mené à la transformation de plusieurs peuplements mixtes d’Amérique du Nord en peuplements dominés par des conifères ou des feuillus. Le but de cette étude était d’examiner la dynamique des trouées dans le couvert de peuplements mixtes composés de sapin baumier (Abies balsamea (L.) Mill.) et de bouleau jaune (Betula alleghaniensis Britt.) pour améliorer la compréhension des mécanismes potentiels de coexistence entre les espèces. La proportion des trouées dans les 12 peuplements étudiés se situait entre 9 % et 30 % de la superficie totale des peuplements alors que les trouées couvraient de 20 à 2 100 m². La mortalité du sapin baumier était la cause principale de la formation des trouées. Le sapin baumier et l’érable à épis (Acer spicatum Lamb.) dominaient les strates de régénération formées respectivement par des arbres et des arbustes. La compétition exercée par les arbustes ralentit le repeuplement naturel des trouées par des espèces arborescentes. Nos résultats indiquent que le bouleau jaune est l’espèce la plus abondante dans les trouées de plus de 800 m² alors que le sapin baumier domine les trouées de moins de 200 m². Des modèles de transition ont indiqué que la longévité supérieure du bouleau jaune par rapport à celle du sapin baumier assure son maintien dans la strate dominante. La coexistence des espèces dominantes est donc le résultat de l’utilisation différente des ressources disponibles en fonction du temps et de l’espace. L’aménagement forestier devrait maintenir la variabilité de l’âge et de la taille de la récolte parce l’utilisation d’une seule taille de trouée ou d’un seul âge de récolte mènera à un déséquilibre dans la proportion des espèces par rapport à ce qui est observé dans les peuplements naturels. © 2007 NRC tous droits réservés.
Laurence Bourgeois, Stephen Yamasaki, Suzanne Brais, Daniel Kneeshaw, Nicolas Bélanger, Louis Imbeau. How do Alberta’s, Ontario’s and Quebec’s forest operation laws
respect ecological sustainable forest management
criteria in the boreal forest? 2007. For. Chron. 83(1):61-71.
In order to receive forest certification and to respond to societal desires,many forest companies are attempting to demonstrate
that their forest activities are «sustainable». The main objective of this paper is to qualitatively evaluate the ways in
which forestry-related provincial regulations in the three provinces (Alberta, Ontario and Quebec) that contain most of
the Canadian boreal forest help forest companies achieve certification with respect to ecological criteria. In the process of
continually evolving towards sustainable forest management,we evaluate how these provincial regulations governing forest
operations can be helpful in maintaining three criteria: biodiversity, the aquatic environment and soils. This study
shows that the regulations evaluated have varied in their approach and thus have different strengths that must be underlined:
(1) Ontario’s approach is the strongest in terms of biodiversity, (2) Alberta and Ontario provide measures to abandon
roads after harvesting, (3) Quebec provides the greatest specific measures for protecting waterways and aquatic
species, (4) Alberta shows the greatest consideration for maintaining the most soil properties and functions. Better links
between different regulations are necessary in all jurisdictions. The continual improvement of Canadian forest rules is
often slow and advances at a different pace depending on regulators but it should be supported in all provinces.
Afin d’obtenir une certification forestière et de répondre aux besoins de la société, les compagnies doivent démontrer que
leurs activités forestières sont «durables». L’objectif principal de cet article est d’évaluer de quelles façons les normes
forestières provinciales des ministères des ressources naturelles aident les compagnies forestières à obtenir une
certification environnementale.Nous avons évalué de façon qualitative les lois encadrant les opérations forestières en forêt
boréale, la zone forestière dominante au Canada. Nous mettons l’emphase sur trois provinces (Alberta, Ontario et
Québec) qui couvrent la plus grande proportion de la zone boréale au pays. Dans une démarche d’amélioration continue,
nous évaluons comment ces normes peuvent aider à maintenir trois critères : la biodiversité, le milieu aquatique et les sols.
Cette étude montre que ces règlements présentent des différences dans leurs approches et des forces qui doivent être
soulignées : (1) l’approche de l’Ontario est la plus forte en termes de biodiversité, (2) l’Alberta et l’Ontario proposent des
mesures pour abandonner les routes suite aux activités de récolte, (3) le Québec offre les meilleures mesures spécifiques
pour un nombre de milieux humides et d’espèces aquatiques, (4) l’Alberta présente la meilleure réflexion sur le maintien
du plus grand nombre de propriétés et fonctions des sols. De meilleurs liens entre les différentes lois sont nécessaires bien
qu’il faille appuyer l’amélioration continue des règlements forestiers au Canada.
Eve Lauzon, Yves Bergeron, Daniel Kneeshaw. Reconstruction of fire history (1680–2003) in Gaspesian
mixedwood boreal forests of eastern Canada. 2007. For. Ecol. Manage. 244(1):41-49.
We describe the fire regime in the Gaspesian mixedwood boreal forest in order to improve our knowledge of the maritime fire regime through
time and the role of climate on changes in fire cycle. We also investigated the importance of coarse scale spatial factors, such as topography,
altitude, soil-type and vegetation-type. Fire history was reconstructed for a 6480-km² area using Quebec Ministry of Natural Resource archival data
and aerial photographs combined with dendrochronological data, collected using a random sampling strategy. Physiographic features were not
found to significantly influence the fire cycle, but an increase in the cycle (from 89 to 176 years p 0.0001) was observed since the end of Little Ice
Age (LIA) (1850). Relative agreement between the archival data (1920–2003) and the semi-parametric survival analysis approach for the 1850–
2003 period provides greater confidence in our determination of a fire cycle situated between 170 and 250 years. An analysis of fluctuations in the
Canadian forest fire Weather Index system, calculated for the period 1920–2003, showed a statistically significant decrease in extreme values.
Given such a long fire cycle and in the context of forest management based on natural disturbance, even-aged management under short rotations
should be questioned in these mixedwood boreal forests.
© 2007 Elsevier B.V. All rights reserved.
Ronald Charles Drever, Micheal Flannigan, Eve Lauzon, Alain Leduc, Daniel Lesieur, Daniel Kneeshaw, Kimberly Logan, Yves Bergeron, Dominic Cyr, Héloïse Le Goff, Sylvie Gauthier. Past, current, and future fire frequencies in Quebec's commercial forests: implications for the cumulative effects of harvesting and fire on age-class structure and natural disturbance-based management. 2006. Can. J. For. Res. 36(11):2737-2744.
DOI : 10.1139/X06-177
Abstract: The past decade has seen an increasing interest in forest management based on historical or natural disturbance dynamics. The rationale is that management that favours landscape compositions and stand structures similar to those found historically should also maintain biodiversity and essential ecological functions. In fire-dominated landscapes, this approach is feasible only if current and future fire frequencies are sufficiently low compared with the preindustrial fire frequency, so a substitution of fire by forest management can occur without elevating the overall frequency of disturbance. We address this question by comparing current and simulated future fire frequency based on 2 × CO2 and 3 × CO2 scenarios to historical reconstructions of fire frequency in the commercial forests of Quebec. For most regions, current and simulated future fire frequencies are lower than the historical fire frequency, suggesting that forest management could potentially be used to maintain or recreate the age-class distribution of fire-dominated preindustrial landscapes. Current even-aged management, however, tends to reduce forest variability by, for example, truncating the natural age-class distribution and eliminating mature and old-growth forests from the landscape. Therefore, in the context of sustainable forest management, silvicultural techniques that retain a spectrum of forest compositions and structures at different scales are necessary to maintain this variability and thereby allow a substitution of fire by harvesting.
Résumé :Au cours de la dernière décennie, un intérêt grandissant pour le développement d'approches d'aménagement basées sur notre compréhension de la dynamique historique des perturbations naturelles s'est manifesté. Ces approches reposent sur l'idée qu'un aménagement favorisant une composition des paysages et une structure des peuplements similaires à celles créées dans les forêts passées devrait aussi maintenir la diversité biologique et les fonctions écologiques essentielles de ces mêmes paysages et peuplements. Dans les paysages contrôlés par les feux, cette approche est possible seulement si les fréquences de feux actuelles et futures sont suffisamment faibles lorsque comparées aux fréquences pré-industrielles, cela afin de permettre de substituer le feu par la coupe forestière. Nous évaluons cette possibilité en comparant les fréquences de feux actuelles et futures aux fréquences historiques à partir d'études réalisées dans la forêt commerciale québécoise. Les fréquences actuelles et futures des feux, simulées en utilisant deux scénarios de concentration de CO2 (2× et 3× la concentration actuelle), sont plus faibles que les fréquences passées pour la majorité du territoire, suggérant que l'aménagement forestier pourrait potentiellement être utilisé afin de recréer la structure d'âge de la forêt soumise à un régime de feux sévères. Les aménagements équiennes actuels tendent toutefois à réduire la variabilité naturelle du système: par exemple, un aménagement équienne amputera, à terme, la structure d'âge de la forêt naturelle éliminant ainsi les forêts surannées et anciennes du paysage. Le développement de techniques de sylviculture permettant le maintien d'un spectre de compositions et structures forestières à différentes échelles de paysage est une des avenues proposées afin de maintenir cette variabilité. ©2006 NRC Canada
Yves Bergeron, Eve Lauzon, Daniel Kneeshaw, Sylvie Gauthier. Fire cycles and forest management: An alternative approach
for management of the
Canadian boreal forest. 2006. Sustainable Forest Management Network (SFMN). 18 p.
Forest managers in Canada urgently require solutions for achieving the goals of
sustainable development and the conservation of biodiversity. To attain these goals,
many have suggested the use of landscape pattern resulting from naturally
occurring disturbances as a template for forest management. Forest fires constitute
one of the main disturbances affecting forest dynamics in the boreal. Fire cycle
studies have revealed the high variability of this parameter from one region of
boreal forest to the next. Fire cycle is often used as a forest management tool, but
since it is highly variable in time and space, using the mean time since fire seems
to be a simpler and more realistic approach.
Published literature was used to determine both fire cycle and mean time since
last fire of forests across the Canadian boreal forest. Based on the mean time since
fire of the stands, the percentage of forest which could be managed to reproduce
the fire controlled age structure conditions found for each Canadian region studied
was determined. This report provides forest managers with a tool that can be used
to help achieve sustainable forest management and the conservation of
Mathieu Bouchard, Yves Bergeron, Daniel Kneeshaw. Forest dynamics after successive spruce budworm outbreaks in mixedwood forests. 2006. Ecology 87(9):2319-2329.
In order to assess the long-term spatiotemporal influence of the spruce
budworm in sub-boreal mixedwood forests, we studied the effect of three successive outbreaks
in a region of western Quebec, Canada. We used dendrochronology to detect past outbreaks in
three areas (111–185 ha), based on the recruitment age of balsam fir (Abies balsamea) and on
growth patterns of white spruce (Picea glauca), the two main host species of this defoliating
insect. We also used a series of aerial photographs taken between 1935 and 2003 to evaluate
overstory mortality and post-outbreak succession patterns in these same areas. Individual
outbreaks had a spatially homogenous impact on host species throughout the region, but
successive outbreaks differed in intensity: the two outbreaks around 1910 and 1980 caused
widespread mortality in the overstory, but an outbreak around 1945 had little impact,
probably because the forest mosaic had not yet recuperated from the 1910 outbreak. No clear
outbreak was detected in the later part of the 19th century. In portions of the study areas
where the 1910 outbreak had a major impact, between 36% and 50% of the stands were
reoccupied by balsam fir stands in the period up to the 1980 outbreak (cyclic succession), the
rest being at least partly replaced by nonhost species such as Betula spp. Changes in forest
composition after the 1910 outbreak were mostly associated with upper-slope positions in all
study areas. The 1980 outbreak also had a higher impact than earlier outbreaks in lower-slope
positions dominated by black spruce (Picea mariana)–balsam fir mixtures. These results
suggest that, at the regional scale, the abundance of mature or over-mature balsam fir stands
does not determine the outbreak cycle. When an outbreak occurs, however, its impact will be
strongly constrained by forest characteristics such as stand composition and structure, which
are themselves influenced by previous disturbances and slope position.
Yves Bergeron, Mathieu Bouchard, Daniel Kneeshaw. Mortality and stand renewal patterns following the last spruce budworm outbreak in mixed forests of western Quebec. 2005. For. Ecol. Manage. 204(2-3):297-313.
DOI : 10.1016/j.foreco.2004.09.017
We studied mortality caused by the last spruce budworm (Choristoneura fumiferana Clem.) outbreak (1972-1984) and the subsequent regeneration processes in the mixed conifer-hardwood forest zone of the Temiscamingue region, western Quebec. Three kinds of late successional stands, undisturbed by human activities and representative of forest conditions on different sites. Were studied using permanent plots, dendrochronology, and field data. The tree species affected directly by the spruce budworm, balsam fir (Abies balsamea L.), white spruce (Picea glauca Wench.), and black spruce (Picea mariana Mill.) suffered high overall mortality rates during the 1972-1996 period covered by the permanent plot measurements (97.6. 63.5. and 59.6%. Respectively). The mortality of balsam fir and white spruce were positively correlated with pre-outbreak balsam fir basal area in the plots, as was the mortality of a non-host species, white birch (Betula papyrifera Marsh.). Mortality of host and non-host species following the outbreak might have been due in part to modified environmental conditions following canopy disruption. Particularly on imperfectly drained sites that were dominated by balsam fir before the outbreak. This is also supported by the fact that radial increments of surviving white spruce trees remained significantly, lower after the outbreak in balsam fir-dominated stands compared with other stand types. The outbreak has also favoured the emergence of an abundant sapling layer mostly dominated by balsam fir. Due to important fluctuations in the shape of canopy gaps over the years. The correlations between sapling abundance and actual canopy openings are low for all sapling species. In the present-day mixed species stands. Density, and species composition of the sapling layer seem to depend more on the presence of suitable micro-sites than canopy openings. These results suggest that the last outbreak gave rise to a gradient of stand regeneration patterns, depending on species composition before the outbreak and host and non-host mortality following it, ranging from overall stand mortality and replacement in balsam fir-dominated stands, dual-cohort structures in mixed boreal stands where mortality was partial and quasi-gap dynamics in mixed hardwood stands dominated by yellow birch (Betula alleghaniensis Britton). © 2005 Elsevier B.V. All rights reserved.
Andrew Park, Yves Bergeron, Alain Leduc, Daniel Kneeshaw. Spatial relationships and tree species associations across a 236-year boreal mixedwood chronosequence. 2005. Can. J. For. Res. 35(3):750-761.
DOI : 10.1139/x04-199
We studied community development and mortality among tree species at multiple spatial scales in a 236-year mixedwood chronosequence at Lake Duparquet, Quebec. Spatial relationships, species associations, and understory–overstory replacement patterns were studied using spatial statistics, patch indices, G tests, and transition matrices. Results of these analyses showed that shade-intolerant and shade-tolerant tree communities formed increasingly fine-grained patches in midsuccession. These fine-grained associations appear to be partly due to suppressed stems being released into a slowly thinning canopy and partly due to new recruitment of shade-tolerant conifers. In 1-ha plots, tree species richness and evenness peaked in 25-, 100-, and 400-m² subplots during midsuccession. Forest cover type diversity also peaked in midsuccessional landscapes assessed using aerial photographs. The oldest 1-ha plot was dominated by monospecific patches of eastern white cedar (Thuja occidentalis L.), which was the most likely replacement for live and dead trees and the most abundant species in the numerous subplots that were occupied by trees smaller than 8 cm DBH. In spite of this dominance, long-lived paper birch (Betula papyrifera Marsh.) and residual fir (Abies balsamea (L.) Mill.) seedlings may maintain the mixedwood character of this stand into the future. The implications of our findings for stand management and conservation are discussed.
Les auteurs ont étudié le développement et la mortalité de communautés d'arbres en peuplements mixtes à plusieurs échelles spatiales dans une chronoséquence de 236 ans au lac Duparquet, Québec. Les relations spatiales, les associations d'espèces et les patrons de remplacement entre les espèces du couvert dominant et celles du sous-bois ont été étudiés en utilisant des statistiques spatiales, des indices d'agglomération, des tests de G et des matrices de transition. Les résultats de ces analyses montrent que les communautés d'arbres intolérants et tolérants à l'ombre forment un nombre croissant d'agglomérations de petites tailles à l'étape du milieu de la succession. La formation de ces associations de petites tailles semble partiellement attribuable, d'une part, aux tiges opprimées qui sont libérées à l'intérieur d'un couvert qui s'éclaircit lentement et, d'autre part, au recrutement de conifères tolérants à l'ombre. Dans des parcelles de 1 ha, la richesse en espèces et l'équitabilité ont culminé dans des sous-parcelles de 25, 100 et 400 m² de peuplements parvenus à l'étape du milieu de la succession. La diversité du type de couvert forestier estimée à partir de photographies aériennes a aussi culminé sur des territoires parvenus à l'étape de milieu de succession. La plus vieille placette de 1 ha était dominée par des agglomérations monospécifiques de thuya occidental (Thuja occidentalis L.), l'espèce la plus susceptible de remplacer les arbres morts et vivants et l'espèce la plus abondante dans les nombreuses sous-parcelles occupées par des arbres dont le DHP est inférieur à 8 cm. Malgré cette dominance, les espèces à forte longévité que sont le bouleau à papier (Betula papyrifera Marsh.) et les semis résiduels de sapin baumier (Abies balsamea (L.) Mill.) peuvent maintenir la mixité d'espèces de ce type de peuplement dans le futur. Les implications de nos résultats sont discutées en regard de l'aménagement et de la conservation des forêts. ©2005 NRC Canada
André de Römer, Mathieu Bouchard, Christian Messier, Daniel Kneeshaw. A comparison of gap characteristics in mixedwood old-growth forests in eastern and western Quebec. 2005. Can. J. For. Res. 35(10):2510-2514.
DOI : 10.1139/x05-125
Canopy gaps play an important role in the dynamics of old-growth forests, although it is not well known how gap dynamics differ among regions. To further our understanding of natural gap dynamics in mixedwood forests, this study compares mixed stands located in eastern (Gaspésie region) and western (Témiscamingue region) Quebec. We tested whether the gap fraction in mixedwood stands was similar in these two regions. Data from field transects were used to characterize current canopy gaps, and aerial photos were used to contrast gap characteristics before and after the most recent spruce budworm (Choristoneura fumiferana Clem.) outbreak, which occurred from 1973 to 1991 in Gaspésie and from 1972 to 1984 in Témiscamingue. The current gap fraction was found to differ between the two regions: it varied from 2% to 48% with an average of 25.6% for the Gaspésie region and from 24% to 52% with an average of 36.6% for the Témiscamingue region. While the last spruce budworm outbreak coincided with a significant increase in canopy openings in the Témiscamingue region (p = 0.047), no such effect was observed in Gaspésie. These results suggest that the temporal pattern of small-scale disturbances can vary among regions, even when similar forest types are compared.
On sait que les trouées de canopée sont importantes pour la dynamique des peuplements de fin de succession, mais nous disposons de peu d'informations sur la variabilité inter-régionale. Dans le but d'améliorer nos connaissances sur la création des trouées en forêt mixte, cette étude compare des peuplements mélangés de l'est (Gaspésie) et l'ouest (Témiscamingue) du Québec. Nous avons vérifié si le pourcentage d'ouverture de la forêt, pour un même type de forêt, est similaire dans ces deux régions. Des données provenant de transects établis sur le terrain on permis de caractériser les ouvertures actuelles, et des photographies aériennes ont été utilisées pour comparer la proportion de trouées avant et après la dernière épidémie de tordeuse des bourgeons de l'épinette (Choristoneura fumiferana Clem.), qui a eu lieu entre 1973 et 1991 en Gaspésie et de 1972 à 1984 au Témiscamingue. Les résultats obtenus indiquent que le degré d'ouverture de la canopée diffère entre les deux régions : en Gaspésie, le pourcentage d'ouverture de la forêt varie de 2 à 48 % avec une moyenne de 25,6 % alors qu'au Témiscamingue il varie de 24 à 52 % avec une moyenne de 36,6 %. Alors que la dernière épidémie de tordeuse des bourgeons de l'épinette a coïncidé avec une augmentation significative des ouvertures de canopée dans le Témiscamingue (p = 0,047), un tel effet n'a pas été observé en Gaspésie. Ces résultats suggèrent que le taux de création de petites ouvertures peut varier entre les régions, même lorsque des types forestiers similaires sont comparés. ©2005 NRC Canada
Daniel Grenier, Yves Bergeron, Daniel Kneeshaw, Sylvie Gauthier. Fire frequency for the transitional mixedwood forest of Timiskaming, Quebec, Canada. 2005. Can. J. For. Res. 35(3):656-666
DOI : 10.1139/x05-005
Fire history was reconstructed for a 2500-km² area at the interface between the boreal coniferous and northern hardwood forests of southwestern Quebec. The fire cycle, the time required for an area equal to the study site to burn once over, was described using a random sampling strategy that included dendrochronological techniques in conjunction with provincial and national government archival data. Physiographic elements were not found to spatially influence fire frequency; however, human land-use patterns were observed to significantly affect the fire frequency. A temporal shift in fire frequency was also detected, which coincided with the period of Euro-Canadian colonization and known extreme dry years for the study site. Additionally, a fire-free period was identified in the most recent times that could be associated with fire suppression and climate change. The estimated cycles (approx. 188–314 years) for the southeastern section of the study area were thought to better represent the natural cycles for this transition zone as a result of less anthropogenic influence. The importance of gap-type dynamics becomes evident with the increased presence of old-growth forest, given the derived fire cycle estimations for the region. Even-aged management with short rotations, consequently, is questioned because fire cycle estimations suggest more complex harvest systems using an ecosystem management approach.
L'historique des feux a été reconstruit pour une superficie de 2500 km² à l'interface entre la forêt boréale et la forêt feuillue septentrionale du sud-ouest du Québec. Le cycle de feu (nombre d'années requises pour que soit brûlée une superficie équivalente au territoire à l'étude) a été décrit avec un dispositif d'échantillonnage aléatoire utilizant la dendrochronologie conjointement avec les archives des gouvernements provincial et fédéral. Les éléments physiographiques n'ont pas eu d'influence spatiale sur la fréquence des feux. Cependant, les patrons d'utilization des terres associés à la colonization ont significativement affecté la fréquence des feux. Un changement temporel dans la fréquence des feux a été aussi détecté. Il est synchrone avec la période de colonization euro-canadienne, ainsi qu'avec des années de sécheresse extrême pour le site d'étude. De plus, l'absence de feu notée depuis 1950 pourrait être expliquée par l'effet cumulé de la suppression du feu et des changements climatiques. Les cycles estimés (approx. 188 à 314 ans) pour la section sud-est du site d'étude ayant subi une moins grande influence anthropique représenteraient mieux les cycles naturels du territoire étudié. Avec la présence d'une proportion plus élevée de forêt ancienne, les perturbations secondaires par trouées deviennent sont importantes étant donné les estimations du cycle de feu dans la région. Par conséquent, les régimes d'aménagement équienne à rotation courte sont à remettre en question pour ce secteur. Comme le suggère les estimations du cycle de feu, des pratiques sylvicoles plus diversifiées et l'utilization d'une approche de gestion écosystémique seraient plus appropriées. ©2005 NRC Canada
Daniel Kneeshaw. La représentativié: un nouveau concept en conservation des ressources forestières. 2005. L'Aubelle 149:29-30.
En examinant l'histoire de la conservation au Québec, on se rend compte que le population a généralement mis l'accent sur la protection des éléments considérées beaux ou exceptionnels. Leur motivation vient du désir de maintenir ce qu'ils estiment comme unique ou différent au sein d'un paysage.
Laurence Bourgeois, Stephen Yamasaki, Daniel Kneeshaw, Nicolas Bélanger, Louis Imbeau, Suzanne Brais. Le règlement sur les normes d'intervention dans les forêts du domaine de l'État (RNI) permet-il de respecter les critères de l'aménagement durable des forêts ? 2004. L'Aubelle 147:22-25.
Dominic Sénécal, Christian Messier, Daniel Kneeshaw. Temporal, spatial, and structural patterns of adult trembling aspen and white spruce mortality in Quebec's boreal forest. 2004. Can. J. For. Res. 34(2):396-404.
DOI : 10.1139/x03-263
Temporal, spatial, and structural patterns of adult trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) mortality were studied in intact 150-year-old stands in the southwestern boreal forest of Quebec. For both species, mortality decreases (number of dead trees/total number of trees) with distance from the lake edge until 100–150 m, from which point it slightly increases. Strong peaks in mortality were found for 40- to 60-year-old aspen mainly between 1974 and 1992. Such mortality in relatively young aspen is likely related to competition for light from the dominant canopy trees. Also, the recruitment of this young aspen cohort is presumably the result of a stand breakup that occurred when the initial aspen-dominated stand was between 90 and 110 years old. For spruce, strong peaks in mortality were found in 110- to 150-year-old trees and they occurred mainly after 1980. No clear explanation could be found for these peaks, but we suggest that they may be related to senescence or weakening of the trees following the last spruce budworm outbreak. Suppressed and codominant aspen had a much higher mortality ratio than spruce in the same height class, while more surprisingly, no difference in mortality rate was found between dominant trees of the two species. Most spruce trees were found as standing dead, which leads us to reject the hypothesis that windthrow is an important cause of mortality for spruce in our forests.
Les patrons de mortalité temporel, spatial et structurel ont été établis pour le peuplier faux-tremble (Populus tremuloides Michx.) et l'épinette blanche (Picea glauca (Moench) Voss) adultes dans des forêts de 150 ans situées dans le sud-ouest de la forêt boréale du Québec. Chez les deux espèces, on observe une diminution de la mortalité (nombre d'arbres morts / nombre d'arbes total) du bord du lac jusqu'à 100–150 m et une faible augmentation par la suite. La mortalité était importante chez les peupliers de 40 à 60 ans et s'était produite entre les années 1974 et 1992. Cette mortalité chez les jeunes peupliers est probablement reliée à la compétition pour la lumière venant des arbres dominants. Le recrutement de cette jeune cohorte de peuplier est présumé être le résultat d'une ouverture assez soudaine du peuplement mature de peuplier entre les années 90 et 110 ans. Chez l'épinette blanche, une mortalité importante fut observée pour les arbres âgés entre 110 et 150 ans et s'est produite surtout après 1980. Nous croyons que cette mortalité est induite par la sénescence des arbres, ou en raison de leur affaiblissement suite à l'épidémie de la tordeuse des bourgeons de l'épinette. Les peupliers supprimés et codominants avaient un taux de mortalité beaucoup plus élevé que les épinettes, mais il n'y avait pas de différence entre les arbres dominants des deux espèces. La plupart des épinettes étaient morts debout, ce qui rejette l'hypothèse voulant que le vent soit une cause importante de mortalité chez l'épinette.©2004 NRC Canada
Vincent D'aoust, Yves Bergeron, Daniel Kneeshaw. Characterization of canopy openness before and after a spruce budworm outbreak in the southern boreal forest. 2004. Can. J. For. Res. 34(2):339-352.
DOI : 10.1139/x03-278
We propose a simple method that uses aerial photographs to characterize the impacts of a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak on canopy structure. Using aerial photographs taken at the beginning (1972) and after (1994) a major spruce budworm outbreak (1970–1987), we evaluated the change in canopy openness that occurred during the period of the outbreak, in five compositionally different stands. We compared canopy openness evaluated by photointerpretation with two independent field techniques and found a high degree of similarity between methods. Interpretation of the 1972 photographs (prior to the outbreak) shows that regardless of composition, four of our five analysed stands had about the same degree of mean canopy openness (17%–20%). Following the outbreak, openness increased in all stands except for the hardwood-dominated stand. The highest increase in openness (from 18% to 45%) occurred in the stand with the highest conifer content. Thematic maps and spatial analysis techniques were used to describe canopy openness distribution. Openness was low and uniformly distributed before the outbreak, whereas after the outbreak, the various degrees of openness had a patchy distribution in most stands. Furthermore, patch size increased with conifer content. Using the amount of increase in canopy openness and its specific distribution within stands, we propose guidelines for the development of silvicultural practices that mimic spruce budworm disturbances in boreal mixedwoods.
Cette étude propose une méthode simple qui utilise l'interprétation de photos aériennes pour caractériser les impacts d'une épidémie de la tordeuse des bourgeons de l'épinette (Choristoneura fumiferana (Clem.)) sur la structure du couvert forestier. En utilisant des photos prises au début (1972) et après (1994) l'épidémie majeure qui a frappé notre secteur de 1970 à 1987, nous avons évalué les changements dans le degré d'ouverture du couvert forestier qui se sont produits dans cinq peuplements de composition différente. La méthode d'évaluation du degré d'ouverture par photo-interprétation a été comparée à deux méthodes d'estimation utilisées sur le terrain. L'interprétation des photos prises au début de l'épidémie montre qu'indépendamment de la composition, quatre des cinq peuplements étudiés avaient approximativement le même pourcentage d'ouverture moyen (17–20 %). L'épidémie a entraîné une augmentation du degré d'ouverture dans tous les peuplements à l'exception du peuplement dominé par les feuillus. Sur les photos prises après l'épidémie, l'ouverture augmente en fonction de la proportion de conifères. Le peuplement le plus affecté a atteint un degré d'ouverture de 45 % en 1994. L'analyse spatiale de nos résultats révèle que les degrés d'ou verture variables trouvés après l'épidémie sont distribués en îlots alors qu'ils étaient faibles et distribués uniformément avant l'épidémie. La taille de ces îlots augmente avec l'âge des peuplements. Ces résultats nous permettent de proposer un scénario préliminaire de pratiques sylvicoles basées sur les impacts causés par une épidémie de la tordeuse des bourgeons de l'épinette en forêt boréale mixte.©2004 NRC Canada
Laurence Bourgeois, Daniel Kneeshaw. Evaluation of the links between forest operations laws and the sustainable forest management indicators in Alberta, Ontario & Quebec. 2003. Sustainable Forest Management Network (SFMN). 77 p.
Daniel Kneeshaw, Sylvie Gauthier. Old growth in the boreal forest: A dynamic perspective at the stand and landscape level. 2003. Environ. Rev. 11:S99-S114.
Old-growth forests have been identified as a potentially important stage of stand development for maintaining biodiversity in the landscape, yet they have also been targeted by the forest industry in their drive to regulate the forest. We will attempt to propose a definition of old growth, applicable throughout the North American boreal forest, that takes into account the dynamic nature of forest development and that could be useful for management and conservation purposes. We define the start of the old-growth stage as occurring when the initial post-disturbance cohort begins dying off, concurrent with understorey stem recruitment into the canopy. We propose that species longevity and the regional fire cycle can be used to assess the extent of this phase in different regions. Using published data on fire history, we show that the amount of old growth expected to occur in western and central Canada is less than in eastern Canada, where most stands (in area) escape fire for periods longer than that necessary to incur substantial mortality of the initial cohort. At the stand level, we show that the old-growth stage is characterized by small-scale disturbances that engender gap dynamics. Until recently, this process had not been studied in the boreal forest. The old-growth index we present suggests that the relationship between time since the last major disturbance and old-growth status varies most in areas that have not been disturbed for long periods. Both management and conservation strategies have to take into account that old-growth forests are dynamic. To be effective, reserves should contain all stages of development and should be sufficiently large to encompass rare but large disturbances. The abundance of old growth in many boreal regions of North America also suggests that forest management strategies other than even-aged, fully regulated systems have to be developed.
Yves Bergeron, Alison Munson, Louis Imbeau, Louis Bélanger, Luc Bouthillier , Luc Sirois, Daniel Kneeshaw, Alain Leduc, Marcel Darveau, Pierre Drapeau, Brian Harvey, Christian Messier. Modification du RNI - une timide ouverture à une gestion plus adaptée aux réalités régionales. 2002. L'Aubelle 140:20-21.
Stephen Yamasaki, Alison Munson, F Dorion, Daniel Kneeshaw. Bridging boundaries among disciplines and institutions for effective implementation of criteria and indicators. 2002. For. Chron. 78(4):487-491.
The development of a coherent system of criteria and indicators (C&I) requires collaboration and communication among scientists, government, the public, certifying organizations, and the forest industry. It also demands the integration of knowledge from many fields of study, which is foreign to the disciplinary nature of most forestry research. There needs to be greater effort to link groups of indicators and to favour those that are assimilative in nature. Modelling tools adapted to a multi-disciplinary approach and collaborative development will help to integrate knowledge from various fields and institutions. Specific challenges for implementation of C&I have been identified, including: leadership and vision in the evolution towards sustainable forest management (SFM); linking of grass-roots and higher level CI initiatives; streamlining and co-ordinating different certification initiatives and agencies; technology transfer; and collaboration among disciplines.
Yves Claveau, Pierre Drapeau, Daniel Kneeshaw, Brian Harvey. Le modèle forestier Finlandais est-il toujours un exemple à suivre? 2001. L'Aubelle 136:14-24.
Stephen Yamasaki, Marie-Josée Fortin, Daniel Kneeshaw, Alain Leduc, Christian Messier. Développement d'indicateurs et d'outils d'évaluation de GDF à une échelle opérationnelle: un défi d'intégration. 2000. L'Aubelle 134:10-14 et 135:19-26.
Philip J. Burton, David Coates, Daniel Kneeshaw. Managing forest harvesting to maintain old growth in boreal and sub-boreal forests. 1999. For. Chron. 75(4):623-631
Old-growth stands can be rare in northern coniferous forests, and hence are worthy of protection and special management. We describe some quantitative guidelines for recognizing old-growth stands and options for maintaining a long-term supply of old-growth values in landscapes managed for timber production. In the Sub- Boreal Spruce forests of central British Columbia, attributes most indicative of old-growth status include stand age, the den- sity of large (>1.0 m3) snags and downed logs, stand basal area and volume. It is suggested that partial cutting could occur in some old-growth stands, while still maintaining their structural and func- tional attributes, if large logs, snags and trees are retained at the threshold densities necessary to recognise old-growth status. At the landscape level, the use of extended timber crop rotations is advocated. Planning for a tapered forest age class distribution (with decreasing areas of forest allowed to persist to successively older ages) is suggested as a means of sustainably generating true old-growth, and as an alternative to the use of partial cutting and patch retention. Arithmetic formulas are developed which pro- vide guidelines for the proportion of the forest land base to be kept in each successive age class. This model for regulating human dis- turbance in commercial forests holds promise as a mechanism for allowing continued timber harvest and even-aged stand management while retaining a near-natural proportion of old-growth forest in northern landscapes.
Christian Messier, Daniel Kneeshaw. Thinking and acting differently for a sustainable management of the boreal forest. 1999. For. Chron. 75(6):929-938.
Sustainable forest management has replaced sustained yield as the new management strategy for most countries and forest companies. This concept has generated a lot of interest and discussion, and a great deal of effort is being made to modify current forestry practices to be sustainable. In this paper, we argue that the still somewhat vague concept of sustainable forest management calls for a substantial modification in our way of thinking about and practising forestry. To move toward that goal, we recognize important social and economic challenges to sustainable management and suggest nine essential notions: 1) manage the forest ecosystem as a whole and not in parts nor only for the crop species; 2) conserve a significant proportion of the boreal forest (i.e,, at least 12%); 3) practice intensive forestry on a small portion of the land to recover the fibre lost from notions 1 and 2; 4) strive for innovation in thinking and acting; 5) foster research and development to support notion 4; 6) balance regional needs with that of the global community; 7) encourage public participation; 8) consider the impact of substantial change in climate over the next 100 years (or next rotation); and 9) substitute regulations that are adaptive for those that are restrictive, An example of the kind of silviculture that could be used in ecosystem management for the black spruce forest is also discussed.
Yves Bergeron, Daniel Kneeshaw. Spatial and temporal patterns of seedling recruitment within spruce budworm caused canopy gaps. 1999. Ecoscience 6(2):214-222.
Gap dynamics theory suggests that spatial and temporal patterns of species recruitment within canopy gaps may be due to differences in shade tolerance. Although this theory has been developed in low latitude forests, we suggest that it is also applicable in boreal forests. This study investigates temporal and spatial patterns of seedling and sapling regeneration in canopy,gaps caused by spruce budworm. Tree seedlings, saplings, and shrubs were mapped, measured, and aged in five gaps in a 234-year-old conifer stand in the southern part of the boreal forest. Shade-tolerant fir and cedar seedlings and saplings were found in the southern part of the gaps, whereas intolerant aspen root suckers were associated with the northern part of the gaps. Within gaps, fir seedling and sapling density at the quadrat scale was negatively related to mountain maple cover. A temporal partitioning of seedlings and saplings into pre- and post-gap formation also showed a gradient of species establishment related to shade tolerance. The zone of high tight in the northern part of large gaps may permit the maintenance of shade-intolerant species in these forests. However, the small area of this zone and the slowness of gap formation will limit shade-intolerant species abundance.
Y Ban, H Xu, Yves Bergeron, Daniel Kneeshaw. Gap regeneration of shade intolerant Larix gmelini old-growth boreal forests of northeastern China. 1998. J. Veg. Sci. 9(4):529-536.
Stand mapping and vertical and oblique tree crown projections were used to study gap characteristics and gap effects on the regeneration and stand development of Larix gmelini. The hypothesis is that waves of advance Larix regeneration are recruited into the canopy layer following the creation of canopy openings. In old-growth Larix forests of the northern Da Xingan Ling Mts., at 52 degrees N, obliquely projected gaps (OPG) begin at a distance of 60 - 80 % of the canopy tree height from the southernmost stems bordering the gap and thus the OPGs may extend beyond the northern boundaries of the vertically projected gaps (VPG). Changes in the environment and resource availability in the OPG result in increased Larix sapling survival. Due to a greater incidence of light, 10 - 30 yr old OPG saplings were more abundant than saplings in either a near-oblique projected gap (NOPG) or in the shadow of obliquely projected crowns (SOPC). The survival of saplings more than 30-yr old was highest when they were found in the OPG of one canopy opening and the VPG of another. This means that, following recruitment into an OPG, saplings then require the space found in a VPG to permit growth into the canopy. Thus, various-sized gaps contribute to the survival of different aged saplings by increasing the complexity of stand structure. Although individuals may regenerate in an OPG, successful recruitment into the canopy requires the available growing space of a VPG. This research suggests that shade intolerant Larix gmelini can maintain its canopy dominance without fire via gap regeneration.
Yves Bergeron, Daniel Kneeshaw. Canopy gap characteristics and tree replacement in the southeastern boreal forest. 1998. Ecology 79(3):783-794.
This study identifies patterns in the gap disturbance regime along a successional gradient in the southern boreal forest and uses this information to investigate canopy composition changes. Gaps were characterized in hardwood, mixed-forest, and conifer stands surrounding Lake Duparquet in northwestern Quebec. From 39 to 80 gaps were evaluated along transects established in each of these stands. The abundance of gap makers and gap fillers and total regeneration was evaluated by species, as well as the size of each gap encountered along the transects. The percentage of the forest in canopy gap was calculated directly from the proportion of the transect in gap and by using gap area and line-intercept techniques. Changes in composition were evaluated from gap-maker and gap-filler distributions and by using transition matrices based on species mortality and regeneration in canopy gaps.
The percentage of the forest in canopy gap ranges from 7.1% in a 50-yr-old forest dominated primarily by aspen to 40.4% in a 234-yr-old fir-dominated forest. Gap events are due to individual or small-group tree mortality in the early successional forest but become species-specific events controlled by spruce budworm outbreaks in the later stages of succession. Due to the high latitude, direct light only reaches the forest floor in the very largest gaps of the conifer-dominated stands. However, these gaps form slowly as budworm-caused mortality occurs over a number of years, whereas in aspen-dominated stands gaps are formed quickly by the snapping of tree stems. Balsam fir is the most abundant gap-filling species; however, its abundance is negatively correlated to gap size in all stand types. Markovian transition matrices suggest that in the young aspen-dominated forests small gaps lead to species replacment by more shade-tolerant conifers but that in the oldest forests the larger gaps will result in maintenance of the intolerant species and an increase in the abundance of cedar.
Louis De Grandpré, Daniel Kneeshaw, Yves Bergeron. Early response of Abies balsamea seedlings to artificially created openings. 1998. J. Veg. Sci. 9(4):543-550.
Small-scale canopy openings are being increasingly recognized for their importance in boreal forest stand development. Yet more work is necessary to understand their effects on seedling growth. This study investigated the effect of different degrees of canopy opening (all trees cut, conifers cut, conifers girdled and control quadrats) in different stand types on Abies balsamea seedling recruitment, growth and architecture. The lack of a treatment effect on seedling establishment suggests that gaps primarily affect advance regeneration. In the first year after treatment the seedlings in the cut blocks (both conifer cut and all trees cut) responded with an increase in height growth. Changes in the leader to lateral branch ratio were also significant. Continued architectural change in terms of number of branches produced did not occur until after two years had passed. Although not significantly different from the control, increases can be observed in all measurements for the girdled treatment. It is therefore concluded that the growth response of advance regeneration is more important following canopy opening than new seedling recruitment and that seedling performance is greatest where degree of opening is greatest.
Daniel Kneeshaw. Effets des épidémies de la tordeuse des bourgeons de l'épinette sur la dynamique de la régénération dans la forêt boréale du nord-ouest du Québec. 1997. Thèse de doctorat en sciences de l'Environnement, Université du Québec à Montréal. 136 p.
Les épidémies de la tordeuse de bourgeons de l’épinette (TBE) constituent la principale perturbation naturelle entre deux feux successifs dans les forêts boréales de l’est du Canada. Des intervalles plus longs entre les feux et l’utilisation de la régénération préétablie pour régénérer les forêts exploitées favorisent une augmentation de l’importance du sapin baumier l’hôte de la TBE. Un effet croissantdes épidémies de la TBE sur la dynamique de nos forêts est ainsi attendu.
Suite à la mortalité des arbres adultes, le recrutement des semis vers les strates supérieures assure la fermeture des trouées. La connaissance de la réponse de la régénération aux trouées permettrait donc une meilleure compréhension du rôle de la TBE dans le développement de la forêt. En Abitibi, le lieu de l’étude, dû au régime de feu, les forêts issuent des feux possèdent des peuplements d’âges et de compositions très variables, ce qui leur confèrent différents niveaux de vulnérabilité à la TBE. Il devient donc nécessaire de caractériser l’effet des épidémies de la TBE et la réponse de la régénération préétablie selon les différentes stades successionels.
Ainsi, le premier chapitre de cette thèse vise à déterminer les facteurs écologiques qui influencent l’abondance de la régénération préétablie selon les différents stades de développement de la forêt. Les résultats indiquent que les facteurs abiotiques sont faiblement corrélés à la densité des semis de la plupart des espèces. Par contre, les facteurs biotiques tels que la surface terrière des semenciers, le recouvrement arbustif et la présence des trouées sont liés à l’abondance de la régénération coniférienne. De plus, les semis de sapin baumier et d’épinette blanche sont plus abondants dans les peuplements mixtes d’âge intermédiaire que dans les vieux peuplements conifériens. La quantité de semis d’espèces intolérantes à l’ombre demeure quant à elle faible mais constante à travers les stades successionels. Seul l’abondance du thuya augmente avec la durée du temps après feu. Dans les vieux peuplements conifériens, les trouées causées par la TBE sont grandes, ce qui pourrait permettre le maintien du recrutement des espèces intolérantes à l’ombre.
Le deuxième chapitre a pour objet la caractérisation des régimes de perturbations par les trouées et son influence sur la succession. Un échantillonnage des trouées montre que l’abondance et la superficie de ces dernières sont proportionelles à l’abondance des adultes de sapin baumier ainsi qu’au temps écoulé depuis le dernier feu. Une importante régénération du sapin baumier est aussi associée à des trouées de petites dimension. La modélisation de la succession grâce à des matrices de transition suggère que le sapin remplacera le tremble dans les petites trouées de la forêt de feuillus, mais que dans les grandes trouées des vieilles forêts conifériennes, les feuillus réussiront à se maintenir et que le thuya deviendra plus abondant.
Une étude portant sur la réponse du sapin baumier à des trouées expérimentales est presentées dans le troisième chapitre. Une série de trouées expérimentales ont donc été créés afin d’évaluer l’effet du degré d’ouverture sur la réponse des semis. Quatre traitements présentant différents degrés d’ouvertures de la canopée (témoin, annelage des conifères, coupe de conifères, et coupe totale) de 10m x 10m ont été répliqués dans quatre forêts d’âge et de composition différents. Aucun des traitements n'a eu un effet significatif sur le recrutement de nouveaux semis de sapin. Ceci suggère que l’impact des trouées se répercute surtout au niveau de la régénération préétablie. Même un an après les traitements «coupe conifère» et «coupe totale», les semis ont enregistré une hausse significative de leur accroissement en hauteur et une modification importante de leur architecture. En raison du délai entre le traitement « annelage » et la formation de la trouée, la réponse des semis était plus lente que celle suite aux coupes. La vitesse de la formation des trouées après une épidémie devrait donc aussi avoir un effet sur la réponse des semis.
Dans le chapitre quatre nous présentons les résultats d’une étude des patrons spatiaux et temporels de recrutement à l’intérieur de trouées formées durant la dernière épidémie de TBE dans la forêt la plus affectée. Les résultats montrent que les semis des espèces hôtes pour la TBE s’installent non seulement avant l’épidémie mais aussi durant et après celle-ci. Ce phénomène est probablement dû à la présence de quelques arbres qui survivent à l’attaque de la TBE. Le bouleau s’installe durant la formation de la trouée et le tremble surtout après une ouverture complète. Spatialement, la probabilité de trouver le tremble est plus élevée à la lumière directe au nord de la trouée, tandis que le sapin se retrouve dans l’ombre, au sud de la trouée. L’espèce compétitrice la plus importante, l’érable à épis, limite cependant l’abondance du sapin. En effet, le nombre de semis de sapin diminue avec la proportion d’érable à épis dont le recouvrement est plus important dans les grandes trouées.
L’ensemble des résultats suggère que les grandes trouées formées suite aux épidémies de la TBE sont importantes pour le maintien des espèces intolérantes à l’ombre dans les vieilles forêts. Ces espèces, en particulier le tremble, sont associées avec la région nord de la trouée, où la lumière directe se retrouve. Cependant, à cause du faible angle d’incidence de la lumière et de la formation lente des trouées causées par la TBE, les périodes et les zones de lumière directe sont limitées. C’est en partie pourquoi le sapin, dû à sa tolérance à l’ombre, demeure l’espèce la plus abondante. Seul le thuya semble être capable de déplacer le sapin. Ceci s’explique par sa tolérance à l’ombre mais aussi par sa longevité et par le fait que cette espèce n’est pas un hôte de la TBE. Nos résultats confirment que le thuya augmente en abondance et en proportion dans les vieux peuplements. L’interaction avec les arbustes, surtout l’érable à épis, affecte aussi l’abondance des différentes espèces. © 1997 UQAM tous droits réservés.
voir les plus récentes
Yves Bergeron, Daniel Kneeshaw, Christine Galipeau. Postfire regenereration of white spruce and balsam fir in relation to seedbed and distance from seed sources. 1997. Can. J. For. Res. 27(2):139-147.
The goal of this study was to describe white spruce (Picea glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) recolonization in a forest destroyed in 1923 by an intense fire. Regeneration was evaluated considering both ecological site factors and distance to a seed source. Sampling was conducted along four transects crossing this stand. Each transect began in an unburned zone or at the edge of the intact forest and progressed towards the centre of the 1923 bum taking into account the two types of soil parent materials. Demographic variables of these two species were assessed by dating, using dendrochronology, at least 10 individuals found within each of the quadrats. The area and distance of the quadrats were determined as a function of the changes observed in stand structure and composition. As shown by its age distribution, fir recruitment was low during the first 30 years of succession but increased to higher levels thereafter. Colonization by white spruce is, on the other hand, characterized by two waves of recruitment, the first peak occurring during the initial phase of stand establishment and the second smaller peak occurring later during succession. The two factors found to have the greatest predictive power in determining the regeneration density of these two conifer species are the distance to the preserved zone, and hence to a seed source, and the type of soil parent material, as it determines the receptivity of the germination bed after fire. White spruce benefitted from its ability to recolonize more rapidly than balsam fir by long distance reinvasion of the open site in the initial stage of succession. Balsam fir, on the other hand, recolonizes the site by advancing waves of regeneration in which groups of individuals are established at relatively short distances from parent trees. Although slower to recolonize, balsam fir demonstrates a greater ability for continued long-term recolonization. With respect to the ability to predict the pattern of natural regeneration abundance following fire, the results of this study demonstrate the importance of spatial distribution of seed sources and quality of germination beds as it varies with superficial deposit type. Therefore, these two components should be considered in models predicting forest succession following fire. ©1997 NRC Canada
Daniel Kneeshaw Mot de fermeture et remise des prix 15e colloque annuel du CEF, Université de Sherbrooke, Québec (2022-09-29)
Sabrina Brisson, Kaysandra Waldron, Daniel Kneeshaw, Louis De Grandpré. Facteurs de mortalité chez la régénération préétablie en contexte d'épidémie de tordeuse des bourgeons de l'épinette et de coupes de récupération 15e colloque annuel du CEF, Université de Sherbrooke, Québec (2022-09-28)
Daniel Kneeshaw Mot de bienvenue du Directeur du CEF 15e colloque annuel du CEF, Université de Sherbrooke, Québec (2022-09-28)
Jehova Lourenço Junior, Daniel Kneeshaw. Assessing the wood architecture of conifer species and cell-level adjustments linked to hydraulic safety and efficiency 22e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, complètement virtuel (2020-12-02)
David Grenier-Héon, Changhui Peng, Daniel Kneeshaw. Analyse des patrons de mortalité historiques des arbres de la forêt boréale du Québec dans le contexte des changements climatiques 21e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2019-11-30)
Daniel Kneeshaw, Louis De Grandpré. PRÉSENTATION ANNULÉE :
Influence des stress climatiques et biotiques sur le processus de mortalité de l'épinette noire (Picea mariana) dans la forêt boréale du Québec 21e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2019-11-30)
Daniel Kneeshaw Affiche 10
Influence des stress climatiques et biotiques sur le processus de mortalité de l’épinette noire (Picea mariana) dans la forêt boréale de l’est et l’ouest du Québec. 20e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Lorrainville, Québec. (2018-11-30)
Alexandra Villiard, Daniel Kneeshaw. Affiche 13
Impacts des sécheresses et de la compétition sur la
croissance du sapin baumier en forêt boréale. 20e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Lorrainville, Québec. (2018-11-30)
Guillaume Sainte-Marie, Daniel Kneeshaw. Face à la tordeuse, couper ou ne pas couper ? Là est la question ! 17e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2015-12-02)
Laurent Kerharo, Daniel Kneeshaw, Yves Bergeron. Dynamique des chablis en pessière à mousse 14e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2012-11-29)
Alexander Campbell, Daniel Kneeshaw, Alain Leduc. Indicateurs de la vigueur des épinettes noires en régénération naturelle après coupe dans la pessière noire à mousse 14e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2012-11-29)
Daniel Kneeshaw La prochaine épidémie de la TBE (tordeuse des bourgeons de l’épinette), l'aménagement forestier et les changements climatiques: À quoi doit-on s'attendre? Midi-foresterie (2011-11-08)
Alexander Campbell, Daniel Kneeshaw, Alain Leduc. Analyse des méthodes pour estimer la vigueur des épinettes noires en régénération dans la forêt boréale 12e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2010-11-13)
Julie Fradette, Daniel Kneeshaw, Brian Harvey. Effets des conditions microenvironnementales sur la dynamique de régénération de peuplements mixtes 12e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2010-11-13)
Laurent Kerharo, Daniel Kneeshaw, Yves Bergeron. Chablis en pessière : Impacts sur les peuplements (mortalité et régénération). Affiche scientifique 11e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2009-12-09)
Benoît Gendreau-Berthiaume, Daniel Kneeshaw, Brian Harvey. Coupes partielles et perturbations naturelles en forêt boréale mixte: Similitudes et différences. Affiche scientifique 11e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2009-12-09)
Mathieu Bouchard, Daniel Kneeshaw, Yves Bergeron. Natural dynamics following successive spruce budworm outbreaks in mixed forests of western Quebec (Canada) 5th international Workshop on Disturbance Dynamics in Boreal forests, Dubna, Russie.
Daniel Kneeshaw Évaluation des liens entre le RNI (Règlement sur les normes d’intervention dans les forêts du domaine de l’État) et les critères de l’aménagement durable des forêts. (33 diapos.) 5e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec.
Annick St-Denis, Daniel Kneeshaw, Yves Bergeron. L’ouverture des peuplements de la ceinture d’argile vue sous l’angle de la dynamique des trouées 22ème colloque CONFOR-Innovation. Parc National du Mont Orford, Orford, Québec, Canada.
Daniel Kneeshaw, Christian Messier, Alain Leduc, David Paré, Pierre Drapeau, Yves Bergeron. Towards and ecological forestry: sustainable forest management inspired by natural disturbances 3rd International Workshop on 3rd International Workshop on Disturbance dynamics in boreal forests. Kuhmo, Finland.