Fertilization of hybrid poplar (HP) plantations with papermill by-products is a promising solution to improve soil fertility and nutrient availability, increase plantation productivity, and provide added value to these materials that would otherwise be incinerated or sent to the landfill. We assessed the growth and foliar nutrition of a HP clone (Populus × canadensis × Populus maximowiczii) at six plantation sites aged 3–5 years in southern Quebec, Canada. Sites received a fertilization treatment consisting of a mixture of papermill biosolids (120 to 140 t·ha-1, depending on site) and lime mud (10 to 15 t·ha-1) before being planted, or no fertilization (control). Tree growth was significantly improved by fertilization, with fertilized trees showing a mean annual height increment of 1.3 m (all-site mean; SD = 0.2), compared with 0.5 m (SD = 0.4) for unfertilized trees. Foliar calcium and magnesium increased following fertilization and levels met optimal thresholds at all sites, whereas nitrogen, phosphorous, and potassium concentrations also increased, but nutritional deficiencies remained for these elements at several sites. Our results confirm the benefits of fertilizing hybrid poplars with papermill by-products, but they also indicate that adjustments in application rates or type of by-products could be made to fully satisfy nutritional requirements and thus optimize tree growth. © 2021 Authors Palma Ponce, Miquel, Lafleur, Brais, and Bélanger, and The Crown.

The use of wood ash as a soil amendment in afforestation and reforestation efforts is increasing. While most studies suggest benefits or neutral results on tree growth and survival, a few studies indicate adverse effects. Hybrid larch, jack pine and white spruce were studied at three northwestern Quebec plantation sites after they received wood ash at two application rates. Soil chemical properties, foliar nutrients and seedling growth and mortality were monitored over a period of eight years. The response of soil to ash application was mostly observed in the forest floor and was more pronounced in year 3 than year 8, likely due to the acidifying nature of the boreal soils studied. Jack pine growth increased linearly with wood ash application rates, white spruce growth showed an inconsistent and delayed positive response under the higher application rate, and hybrid larch growth and survival were either increased or decreased under the lower application rate depending of site but decreased at all sites under the higher application rate. The divergence in growth response between tree species underlines a trade-off between species with rapid acquisition of resources (e.g., pine, larch) to species that use more conservative strategies and store nutrients in their tissues for longer periods (e.g., spruce). In the case of hybrid larch, it accumulated larger amounts of Mn in its needles under the higher application rate and thus, the high bioavailability of Mn appears to have been detrimental to its survival and growth. Its higher sensitivity to Mn addition from ash is likely due to its highly acquisitive (nutrients) nature compared to other coniferous species as well as the initial levels of available Mn levels in the soil. The contrasted growth responses reported here under similar growing conditions highlight the importance of identifying suitable species, sites and application rates to maximize the benefits of wood ash amendments for future tree plantations in the boreal forest.

Wood ash amendment to forest soils contributes to the sustainability of the growing bioenergy industry, not only through decreased wood ash waste disposal in landfills but also by increasing soil/site productivity and tree growth. However, tree growth studies to date have reported variable responses to wood ash, highlighting the need to identify proper application rates under various soil/site conditions to maximize their benefits. We explored the influence of tree species, wood ash nutrient application rates, time since application, stand development stage, and initial (i.e., before wood ash application) soil pH and N on short-term tree growth response to wood ash amendment across eight unique study sites spanning five Canadian Provinces. Jack pine (Pinus banksiana Lamb) had the most positive response to wood ash amendment compared to white (Picea glauca Moench), hybrid (Picea engelmannii x glauca Parry), and black spruce (Picea mariana Miller), where increasing nutrient application rates increased height growth response. In comparison, black spruce had the most negative response to wood ash amendment, where increasing nutrient application rates slightly decreased height growth response. Site as a random effect explained additional variation, highlighting the importance of other unidentified site characteristics. By examining trends in short-term growth response across multiple studies with variable site characteristics, we found growth response differed by tree species and nutrient application rates, and that jack pine is a promising candidate for wood ash amendment. These results contribute to our knowledge of optimal wood ash amendment practices and environmentally sustainable bioenergy production. © 2019 The Authors. GCB Bioenergy published by John Wiley & Sons Ltd

Mine wastes create harsh recruitment conditions for forest tree seedlings, especially waste rock piles where erodible slopes are prone to drought. Plantations using fast-growing tree species can potentially accelerate the conversion of degraded mine sites into forests through facilitation of tree recruitment, while contributing to the stability of slopes. In this study, hybrid poplars were tested as a means of achieving reclamation objectives by providing shelter for forest tree seedlings on waste rock slopes (3H:1V ratio) in the Canadian southern boreal region. Density effects of young hybrid poplars were assessed on the emergence and survival of early, mid and late successional species, naturally occurring or hand-seeded, and on the understory micro-environmental parameters in plantations of different spacings (1?×?1, 2?×?2, 4?×?4 m and control without planted trees). Results were also compared in 2?×?2-m plantations with and without a hydroseeded herbaceous cover, traditionally used to control erosion in slopes. During the 2nd growing season of the plantations, seedling emergence of naturally established Salicaceae (Populus and Salix) species followed a quadratic pattern along the density gradient, as emergence values were higher under an intermediary density. Nonetheless, decrease in light transmission emerged as a limiting factor of seedling survival for these early-successional, shade-intolerant species by the next summer. Following a spring sowing experiment in the 3rd growing season of the plantations, emergence rates for later-successional Picea glauca and Abies balsamea seedlings increased with hybrid poplar density. During their peak emergence period, in early season, higher soil moisture content was found under denser cover. However, at the end of the third year of the plantations, only A. balsamea showed moderate increase in early recruitment success rates under denser tree cover. In hydroseeded plots, a competitive effect of the herbaceous cover was observed on Salicaceae emergence and A. balsamea survival. These results suggest that planting of young plantations without a hydroseeded cover may offer a more suitable solution in order to quickly provide early recruitment opportunities for later-successional seedlings in waste rock slopes. Despite this, a significant decrease in moisture content recorded during the second half of the 3rd growing season under the 1?×?1-m cover, compared to the 2?×?2-m, likely signalled an increasing competitive effect from hybrid poplars, which may compromise their nursing potential in the longer term. Therefore, further monitoring is imperative for a better understanding of longer-term facilitation and competition interactions between nurse trees and understory seedlings in waste rock slopes, where competition for limited resources, such as water, may be severe.

Over a period of 2 yr, the effects of dehydrated septic tank sludge application on the chemical properties of a severely disturbed forest clayey soil were assessed and compared with application of native forest floor (i.e., from neighboring forest). Six treatments [fresh and mature sludges × two depths (15 and 25 cm), forest floor, and a control] were replicated three times according to a complete random design. Total organic C and N concentrations of amendments and their chemical structure, based on13 C nuclear magnetic resonance (NMR) spectroscopy, were determined. Mineral soil C and N concentrations and C mineralization rates were monitored as well as nutrient supply rates using Plant Root Simulator™ probes. White spruce [Picea glauca (Moench) Voss] seedling foliar nutrition and growth were also monitored. NMR spectroscopy revealed differences among amendments, with the forest floor spectra displaying lower O-alkyl C and higher alkyl C and carbonyl C proportions relative to sludge. Neither soil C concentrations nor mineralization were significantly improved in the mineral soil under any treatment, even at application rates exceeding 700 t sludge ha?1 (dry mass). The sludges supplied more NO3 and P, and less NH4 and K to the mineral soil than the forest floor and control. Increased nutrient availability under sludge and forest floor generally resulted in improved foliar nutrition and growth of white spruce seedlings. Despite differences in organic matter quality and mineral N form supplied by sludge and forest floor, sludge application is a valid restoration approach. © 2018, Agricultural Institute of Canada. All rights reserved.

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability. © 2017 Springer Science+Business Media New York

The implications of forest floor heterogeneity for fungal activity, nutrient retention and carbon sequestration within the forest floor remain poorly documented. This information would be particularly relevant to situations where large changes in fresh litter occur such as following stand replacing disturbances. Numerous laboratory studies have documented mycelial translocation of simple forms of C and nutrients between contrasting substrates, allowing fungi to overcome local deficiencies. In slightly more complex but less controlled conditions, we assessed how factors contributing to forest floor heterogeneity—decay state, litter origin and tree species—individually affect fungal activity during decomposition. We also assessed how the juxtaposition of litters of contrasting nutrient and C status (decay state) alter fungal activity within individual substrates. We expected fungal biomass to be reallocated to C-rich litters while lignocellulolytic activity would increase in all juxtaposed litters. A microcosm experiment was conducted in which wood and leaf litters of one softwood species (Pinus banksiana) and one hardwood species (Populus tremuloïdes) were incubated alone or in combination with litters of contrasting decay states. Litter mass loss, change in N content, C mineralization, fungal biomass, specific respiration rate and lignocellulolytic activity were measured after 15 and 30 weeks. The decay state of litter had the most pronounced and consistent effects on fungal activity, with higher fungal biomass and lignocellulolytic enzyme activity in well decomposed litters and higher mass loss, C mineralization and specific respiration rate in fresh litters. In juxtaposed litters, fungal biomass was initially reallocated to fresh litters when incubated with well decomposed litters. Cellulolytic activity also increased by 30% in juxtaposed fresh litters while Mn-peroxidase activity increased by 42% in both fresh and well decomposed litters. With the longer incubation period, C mineralization and specific respiration of fungal biomass increased in juxtaposed well decomposed wood, indicating an increase in overflow metabolism presumably in response to an increase in labile C. Fresh litters that were juxtaposed increased their N content while that of single litters decreased. A better understanding of fine scale mechanisms affecting litter decomposition could improve our ability to forecast ecosystem response to disturbance.

In Quebec, reforestation by means of coniferous plantation began in the early 1980 and peaked in 1990. However, one wonders if these efforts bore fruits given the high degree of vegetation competition encountered in some plantations. The study objectives were to evaluate and compare changes in forest cover of coniferous plantations established since 1985 on clay soils in the boreal forest. The evaluation was conducted using vegetation indices extracted from images provided by Landsat TM and ETM + for the periods 2000, 2005 and 2010. Digital ortho-photos and field data were used to assess the effectiveness of these indices. The Tasseled Cap Greenness Index proved to be the most efficient to discriminate the type of cover with a Kappa index of 50%. The results show that over 50% of the plantations were classified as mixed (deciduous – softwood) and 25% were classified as deciduous in 2000, while in 2010, 51 % of plantations were mixed and 11 % deciduous. Using a generalized linear mixed model with Laplace approximation, we have established the relationship between changes in cover, age and type of the plantation. The likelihood of an initial deciduous cover to evolve toward a mixed or coniferous cover was nearly 68 %. The plantation type, its age and cover and their interactions all had significant effects on the probability of a cover to change over time. This project contributed to the assessment of coniferous plantations established between 1980 and 1995 over an area of 18797 ha and confirms that remote sensing tools are effective for tracking large areas while providing quality information for the planning of silvicultural treatments.

This study examines tree and stand response to a gradient of commercial thinning intensities and nitrogen fertilization (200 kg N ha?1) in nine jack pine (Pinus banksiana) stands of Eastern Canada over a period of 14 years. Thinning intensity ranged from 0% basal area removal in control plots to 64% in thinned plots. Tree diameter increment, absolute and relative volume increment and mean volume increased with thinning intensity and were higher in fertilized plots. Individual tree response depended on tree diameter, with smallest trees exhibiting highest relative volume increment to thinning intensity. Stand basal area increment was positively associated to initial stand basal area and negatively to stand age. In thinned and fertilized plots, stand volume increment was higher and natural mortality lower than in fertilized only and unfertilized control plots over the 5–14 year period after thinning. However, the positive effect of fertilization on tree volume increment decreased with thinning intensity. Despite positive individual tree growth responses to thinning and fertilization, residual stand volume increment decreased with increased thinning intensity in both fertilized and unfertilized plots. While total cumulative stand volume (harvested + residual) also decreased with thinning intensity in unfertilized plots, comparable total volumes were observed in fertilized + thinned and unthinned control plots. Nitrogen fertilization in the years following commercial thinning enhanced the benefit of thinning on these relatively poor sites by increasing tree diameter growth, lowering mortality, and increasing total stand merchantable volume compared to unfertilized thinned stands.

In the current context of forest ecosystem management, partial harvesting has been proposed as a silvicultural tool to augment forest variability on managed landscapes and to accelerate the development of structural and compositional attributes of old-growth/late successional stands. The aims of this paper were to (1) identify and characterize, based on the literature, the structural attributes of old-growth aspen-dominated stands in the North American boreal mixedwood forest, and (2) examine the short-term potential of partial harvesting in aspen-dominated stands to accelerate stand development toward these old-growth characteristics. Two stand types – pure aspen (93% aspen basal area) and mixed aspen (81% aspen basal area) – were monitored over a 12-year post-treatment period. The scientific literature suggests that compared to pure, even-aged premature or mature stands, old-growth aspen stands have lower merchantable stem densities and basal area, more large aspen stems, higher stem size variability, more than one cohort of trees, greater percentage area occupied by gaps, higher expanded gap area, and more and larger snags and downed wood. In addition, old-growth aspen mixedwoods characteristically have more shade-tolerant conifers in understory and overstory layers than younger, mature stands. Results of this study indicate that light thinning from below (33% basal area removal) applied in pure aspen stands successfully retained most of the structural attributes of mature aspen stands, but did not generally “accelerate succession” toward old-growth traits in the 12-year time interval since treatment. A dispersed free thinning (45% basal area removal in all merchantable size classes) applied in mixed aspen stands showed its potential to “accelerate succession” by creating canopy gaps similar to old-growth aspen stands and by promoting recruitment of both tolerant and intolerant tree species. Two high intensity partial harvesting treatments, a thinning from above of 61% basal area in pure aspen stands and 400 m2 gap cuts (54% basal area removal) in mixed aspen stands may set back stand development by disproportionally favoring recruitment and growth of intolerant hardwood species.

Mixedwood forests occupy a large extent of boreal regions and have the potential for sequestering large amounts of carbon. In the context of forest ecosystem management, partial cutting prescriptions are increasingly being applied to boreal mixedwood stands. Partial harvesting is expected to maintain carbon pools and dynamics within the limits of those of natural stands. Changes in live tree, deadwood (standing snags, downed logs), forest floor and mineral soil carbon pools were assessed over a 9-year period in a replicated large-scale experiment, which included unharvested controls, two variants of partial harvesting and clear-cuts. We also measured leaf litter and deadwood inputs and decay rates. Carbon flux through leaf litterfall recovered rapidly following partial harvesting. Carbon flux from live trees to deadwood pools was a dominant process in partially harvested stands where snags and downed log carbon pools remained similar to those of natural stands. Hence, the nature of litter inputs diverged strongly among clear-cut and partially harvested treatments. Leaf and wood decay rates were higher in the partial cuts and controls than in clear-cuts. No significant differences in forest floor and mineral soil carbon were observed 9 years after harvesting. Carbon sequestration in live tree biomass was the carbon pool that most strongly differentiated the treatments allowing partial harvesting to maintain forest stands as net carbon sinks.

Wood ash fertilization has yet to be investigated in Canadian boreal forests. Ash often improves soil acid–base status, but without N addition it seldom increases tree growth on poor mineral soils. We report results of a large scale experiment conducted in a boreal jack pine (Pinus banksiana Lamb) stand growing on sandy acidic soil in Northeastern Canada. The experiment was completely random with four replications (1 ha each) of five treatments (0, 1, 2, 4 and 8 dry Mg ha?1) of loose fly ash with and without urea (280 kg N ha?1). Soils were sampled in the 0, 2, and 8 Mg ha?1 treatment up to eight years after application. Foliar nutrition and stand growth were assessed in all treatments one and two years and five years after treatment, respectively.

Even under low ash loading, forest floor exchangeable base cations, pH, and base saturation increased within a year of application. Ash application also resulted in a swift decrease in forest floor organic C and an increase in N potential net mineralization rate. The initial dominant pattern of upper mineral soil properties in relation to ash loading was a curvilinear relationship with the highest values observed in the 2 Mg ha?1treatment. Eight years after ash application, significant linear relationships were found between ash loading and base cations and base saturation in the forest floor and mineral soil (0–10 cm, 10–20 cm). Contrary to N fertilization, ash had no effect on jack pine foliar nutrition and on its five-year growth. However, a decrease of 30% in relative growth rate was observed between the control and the 8 Mg ha?1ash treatment for large (?10 cm DBH) black spruces (Picea mariana (Mill.) BSP). Black spruce is the dominant commercial species of Canadian eastern boreal forests and thus, additional studies are needed to validate the deleterious effect of ash on spruce growth and to elucidate the mechanisms involved.

Multi-cohort-based forest management has been proposed as a strategy to conciliate wood supply and biodiversity conservation objectives. At the stand-level, the approach involves using partial harvesting to generate structurally complex stands, notably in terms of tree age, size and species mixtures, conditions that are not easily integrated into yield tables. Using SORTIE-ND, a spatially explicit stand dynamics model, we simulated 100-year development patterns following different partial harvesting treatments in two trembling aspen (Populus tremuloides Michx)-dominated stands in eastern Canada, one 76-year old (pure aspen) and the other 90 years old (mixed aspen). The two stand types differed primarily in the nature of their understory: pure aspen stands had little advance conifer growth and a dense understory of a woody shrub species whereas mixed aspen stands were characterized by a dense regeneration layer of shade-tolerant conifers. To do this, we first evaluated model performance using short (12 years) and long (168 years) term empirical data. We then modelled stand dynamics following a range of simulated partial harvesting treatments of different intensities (33, 61 and 80% basal area removal), and gap sizes (400, 900 and 1600 m2). Following mortality of the first cohort of aspen, simulations projected dominance of conifer species, white spruce in particular, in unharvested controls of pure aspen stands and balsam fir in mixed aspen stands. Aspen recruitment increased with intensity of partial harvesting. All gap treatments and the 80% dispersed harvesting favored recruitment of aspen over conifer species. After 100-year simulation runs, the 1600 m2 gap treatment resulted in highest stand basal areas, 38.0 and 34.1 m2 ha?1, of which 18% and 28% consisted of intermediate- to shade-tolerant conifer species in pure aspen stands and in mixed aspen stands, respectively. Concerns surrounding partial harvesting have tended to focus on absolute retention levels and standing residence times of trees; however, our results demonstrate that both stand structure and timber production rates are influenced not only by retention levels after partial harvesting but also by spatial configuration of the residual trees. We identified several model functions that are likely responsible for divergences between empirical conditions and those simulated by SORTIE-ND for the boreal mixedwood and suggest specific empirical studies to improve parameter functions of this modelling tool.

Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR-DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (? diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances. © 2014 Springer-Verlag Berlin Heidelberg.

Boreal mixedwood management has shifted from a relatively narrow focus on commercial wood supply to greater consideration of the natural dynamics and multiple ecological services. This recognition has generated interest in ecosystem management approaches that include diversifying and adapting silvicultural practices, including partial harvesting. The effects of partial harvesting on stand dynamics was assessed over a 12-year period in trembling aspen (Populus tremuloides Michx.) dominated stands in northwestern Quebec, Canada. Four treatments were tested: clearcuts (100% basal area (BA) removal); 1/3 partial cut (1/3 PC, 33% BA removal using low thin); 2/3 partial cut (2/3 PC, 61% BA removal using high thin) and controls (0% removal). Aspen sapling recruitment was directly affected by harvesting intensity with 1/3 and 2/3 partial cuts generating 5% and 56%, respectively, of aspen sapling densities in clearcuts. Aspen sapling recruitment increased continuously following clearcut and partial cut treatments with no significant mortality in the sapling layer over the 12-year period. Recruitment of conifer saplings also increased with time and was significantly higher in the two partial cuts than in the clearcut treatment. Twelve years after treatments, mortality of residual aspen stems (?10 cm DBH) reached 250 stems ha?1 12 yr?1 in controls, compared to 106, and 170 stems ha?1 12 yr?1 in 1/3 PC, and 2/3 PC stands, respectively. Initially (1–3 years after treatments), higher overstory aspen mortality was associated with the 2/3 PC treatment. Aspen mortality was strongly associated with small-sized merchantable stems (10–19.9 cm DBH) regardless of treatment. Both partial harvesting treatments had the effect of maintaining mountain maple (Acer spicatum Lamb.), a shade-tolerant, high woody shrub, at densities similar to those in control stands whereas recruitment of mountain maple saplings was negligible in clearcuts due to high aspen recruitment. Our results indicate that (i) heavy-high partial harvesting promotes sapling recruitment of both aspen and conifers when advance regeneration of the latter is present, (ii) because aspen sucker response can be controlled by varying harvesting intensities and stem selection, it is possible to create a range of mixedwood conditions, depending on whether mixed, structurally complex or more regular aspen-dominated stands are desired, and (iii) on rich mixedwood sites, tall woody shrubs could hinder desirable partial harvesting outcomes.

Variable retention harvesting, with a focus on maintaining biological legacies on managed landscapes, has been practised in the trembling aspen (Populus tremuloides Michx.) dominated boreal mixedwood forests for about two decades. However, little attention has actually been given to the growth response of aspen to partial harvesting. This is the first study to report on tree-level volume growth response of aspen after partial or variable retention harvesting in the Canadian boreal forest. During the winter of 1998–1999, an uncut control, clearcut and two partial harvesting treatments – 1/3 partial cut (1/3PC, 33% BA removal using low thin); 2/3 partial cut (2/3PC, 61% BA removal using high thin) – were applied in 75 year old aspen-dominated mixedwood stands in a complete randomized block design. Twelve years after treatment application, 27 dominant and 27 co-dominant trees were collected from unharvested controls and the two partial cut treatments for stem analysis. Annual volume increment (AVI) of individual stems was analyzed as a function of treatment, tree social status, pre-treatment growth, time since treatment application (1–12 years) and neighborhood competition. The latter was estimated using a variety of neighborhood competition indices (NCI). There was no evidence of initial growth stagnation after partial harvesting applications. Only the most severe treatment of partial harvesting (2/3 PC) resulted in an increase in volume increment relative to trees in control stands. Annual increase in volume in the 2/3 partial cut was 25.6% higher than controls over 12 years. AVI of dominant trees was higher by 16.2 dm3 yr?1 than that of co-dominants and was proportional to pre-treatment volume growth. No interaction between treatment and social status or pre-treatment growth was observed. The overall results indicate that competition for resources in these stands is essentially size symmetrical. These results should contribute to the development of silviculture prescriptions that aim to maintain both stand productivity and biological legacies.

Over the last 25 years, greater understanding of natural dynamics in the boreal forest has led to the integration of forest ecosystem management principles into forest policy of several Canadian provinces and, in turn, to greater interest in developing silvicultural treatments that are grounded in natural stand-level dynamics – often referred to as natural disturbance-based silviculture. As a result, alternative silvicultural practices including variants of partial cutting are increasingly being applied in the boreal forest as an approach to balancing economic and ecological management objectives. While the numerous benefits of partial cutting reported in the literature are acknowledged, the objective of this paper is to provide an overview of factors or constraints that potentially limit the application of these practices in boreal Canada in the context of forest ecosystem management and natural disturbance-based silviculture. Among constraining factors, numerous studies have reported elevated mortality rates of residual stems following partial cutting, initial growth stagnation of residual trees, problems related to recruitment of desirable species and, on certain flat or lowland sites, risks of long-term decline in site and stand productivity. A number of operational challenges to partial cutting in the boreal forest are also presented and several avenues of research are proposed.

Renewed interest in biomass harvesting has underscored the need for ecologically relevant thresholds and empirical validation of species responses for deadwood retention if biodiversity is to be preserved in managed landscapes. We experimentally reduced volumes of downed deadwood in clear cut jack-pine stands in Western Quebec, Canada and then monitored changes in spider and ground beetle assemblages 1 and 2-years following biomass removal as well as in uncut stands. We reduced volume of downed deadwood by (1) removing residual deadwood placed on machine corridors during the initial harvest of the stand to minimize soil compaction and (2) removing all residual deadwood material throughout the experimental plots. Ground beetle and spider assemblages from deadwood depleted plots were then compared with those in clearcut plots where no additional biomass had been removed and with uncut stands to assess the incremental effect of overstory removal and subsequent biomass removal using multivariate regression trees. We identified 13,822 individual arthropods representing 177 species. We observed differences in species assemblages attributable to the effects of overstory removal (35% of the explained variance) as well as biomass removal, particularly between plots with intensive removal of biomass and those with no additional or moderate removal of biomass (11% of the explained variance). As expected we observed a range of individual species response patterns. Of particular concern were species that experienced incrementally negative effects of overstory and biomass removal and those that were strongly promoted by biomass removal. These species showed responses atypical of those observed following clear cutting and may fall outside both the range of natural variability observed in this region as well as the range of current forest management intensity practiced in North America.

Partial harvesting has been proposed as a key aspect to implementing ecosystem management in the Canadian boreal forest. We report on a replicated experiment located in boreal mixedwoods of Northwestern Quebec. In the winter of 2000–2001, two partial harvesting treatments, one using a dispersed pattern, and a second, which created a (400 m2) gap pattern, were applied to a 90-year-old aspen-dominated mixed stand. The design also included a clear cut and a control. Over the course of the following eight years, live tree, coarse woody debris, regeneration and ground beetles were inventoried at variable intervals. Our results indicate that all harvesting treatments created conditions favorable to balsam fir (Abies balsamea) sapling growth and trembling aspen (Populus tremuloides) sapling recruitment. However, balsam fir and trembling aspen regeneration and ground beetles response to gap cuts were closer to patterns observed in clear cuts than in dispersed harvesting. The underlying reasons for these differing patterns can be linked to factors associated with the contrasting light regimes created by the two partial harvesting treatments. The study confirms that partially harvesting is an ecologically sound approach in boreal mixedwoods and could contribute to maintaining the distribution of stand ages at the landscape level.

Les chicots et les billes au sol sont des composantes substantielles du réservoir de carbone détritique en forêt boréale. Les effets de leur décomposition sur les caractéristiques physiques et chimiques de la couverture morte restent méconnus. Le principal objectif de cette étude était de caractériser les transformations chimiques des billes et des chicots en décomposition d’espèces d’arbres communes en forêt boréale mixte. Des billes et des chicots de différentes classes de décomposition ont été échantillonnés et analysés par résonance magnétique nucléaire du 13C en phase solide et par spectroscopie dans le proche infra-rouge. Des changements chimiques faibles ou modérés apparaissaient dans les billes et les chicots frais ou modérément décomposés, mais dans les billes bien décomposées, une dégradation substantielle des hydrates de carbone et une augmentation de la concentration en lignines avaient lieu. Les espèces décidues avaient initialement plus d’hydrates de carbone que les conifères, mais la décomposition réduisaient leurs différences, et dans les billes bien décomposées, les espèces ne différaient que par leur teneur en lignines. Les billes bien décomposées des espèces décidues atteignaient des densités de bois très faibles, et leur intégration dans la couverture morte et leur préservation à long-terme restait questionnable. Au contraire, la composition chimique des billes bien décomposées de conifères ressemblait à celle de la couverture morte lignique (c’est-à-dire la couverture morte provenant de la décomposition du bois mort), avec préservation des lignines, des hydrates de carbone et des composés alkylés. Le bois décomposé de conifères contribue à l’hétérogénéité chimique de la couverture morte, favorisant la diversité des décomposeurs et la rétention du carbone dans les sols.

Une quantité importante de carbone dans les sols vient du bois mort mais son rôle dans la séquestration du carbone à long terme, comparativement à celui des litières de feuilles, n’est pas bien documenté dans les forêts boréales de l’Est du Canada. Les objectifs de cette étude étaient de caractériser et de comparer les patrons de perte de masse et les changements dans la composition chimique du bois mort et des litières de feuilles du peuplier faux-tremble (Populus tremuloides Michx.), de l’épinette blanche (Picea glauca (Moench) Voss) et du sapin baumier (Abies balsamea (L.) Mill.) pendant une période d’incubation in situ de 5 à 6 ans, au moyen de sacs de litières, d’analyses par résonance magnétique nucléaire du 13C en phase solide et de la quantification des monomères de lignine par oxydation à l’oxide de cuivre. La limite maximale de décomposition des litières de feuilles et du bois mort était similaire, mais les litières de feuilles se décomposaient plus rapidement, atteignaient la limite maximale de décomposition estimée et convergeaient vers une composition riche en carbone alkyle, phénolique et carbonyle. Au contraire, le bois n’atteignait pas la limite maximale de décomposition estimée, subissait peu de changements chimiques et conservait une teneur élevée en cellulose. A la fin de l’expérimentation, le bois de peuplier faux-tremble avait toujours une concentration en lignine plus faible que celle des conifères, mais des concentrations plus élevées en carbone alkyle et carbonyle. Alors que le bois contribue à augmenter la diversité chimique de la couverture morte, les litières de feuilles, qui conservent un contenu plus élevé en composés alkyles tout au long de la décomposition, pourraient générer une matière organique résiduelle plus récalcitrante.

Environmental change, including human disturbance, can have a striking impact on the biodiversity of ecosystems. We used a molecular fingerprinting technique to determine how communities of saproxylic fungi on trembling aspen deadwood change under the influence of silvicultural treatments designed to emulate natural stand dynamics. We describe changes in richness, diversity, and species composition of fungal communities of trembling aspen logs and snags caused by these silvicultural practices. Our study was conducted in the SAFE Project, a series of silvicultural experiments that tests an ecosystem management model based on natural dynamics. We found that large trembling aspen logs and in advanced decay stages had approximately 9% higher fungal species richness and 10% higher fungal diversity than small and large logs at medium decay stages. The effect of log diameter was in turn strongly dependent on the silvicultural treatment. In burned stands, larger logs supported higher fungal richness and diversity, therefore potentially acting as fungal refuge. A negative relationship between the fungal diversity of logs and snags and the volume of fine woody debris was also related to silvicultural treatments, as fine woody debris increased with silvicultural intensity. Our results underline the negative effects of intense silvicultural practice on fungal diversity and species richness by modifying community composition, but they also highlight the benefits of partial harvest, which retain coarse woody debris volume.

A decrease in the average diameter of commercially harvested tree species in the Eastern boreal forest of Canada has led to a decrease in availability of quality wood for the forest industry. Commercial thinning has been proposed as a means to increase stem diameter growth. However, little is known about physiological responses underlying species responses to thinning. We assessed the effect of canopy opening on the photosynthetic response of mature jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) trees. Two years after thinning and for each species, light response curves and the diurnal course of photosynthesis were characterized from measurements taken in a completely randomized block experiment on current-year and one-year-old needles of 12 trees from stands subjected to different levels of canopy opening. Soil water content, air and soil temperatures, and needle N concentration were not affected by thinning for either species. However, light availability increased with basal area removed and could explain the significantly positive relationship between thinning intensity and diurnal course of photosynthesis for one-year-old needles of jack pine. Black spruce photosynthesis did not respond to increases in light. Light-saturated rate of net photosynthesis (A_max), photosynthetic efficiency (α), light compensation point (LCP), and diurnal respiration (R_d) did not vary with thinning for either of the species. Jack pine and black spruce responses to thinning should be interpreted in light of species autecology.

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.

Coarse woody debris supports large numbers of saproxylic fungal species. However, most of the current knowledge comes from Scandinavia and studies relating the effect of stand or log characteristics on the diversity and composition of decomposer fungi have not been conducted in Northeastern Canada. Logs from five tree species were sampled along a decomposition gradient in nine stands representing three successional stages of the boreal mixed forest of Northwestern Quebec, Canada. Using a molecular fingerprinting technique, we assessed fungal community Shannon–Weaver diversity index, richness, and composition. We used linear mixed models and multivariate analyses to link changes in fungal communities to log and stand characteristics. We found a total of 33 operational taxonomic units (OTUs) including an indicator species for balsam fir (similar to Athelia sp.) and one found only in aspen stands (similar to Calocera cornea). Spruce logs supported the highest fungal Shannon–Weaver diversity index and OTU number. Our results support the hypothesis that log species influences fungal richness and diversity. However, log decay class does not. Stand composition, volume of coarse woody debris, and log chemical composition were all involved in structuring fungal communities. Maintaining the diversity of wood-decomposing communities therefore requires the presence of dead wood from diverse log species.

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.

Dans un contexte où on souhaite réaliser un aménagement forestier plus intensif, le reboisement des terres en friche suscite beaucoup d'intérêt pour les producteurs forestiers. Ces plantations en milieu agricole se compa-rent-elles à celles établies en milieu forestier? Dans cette étude, nous avons comparé les caractéristiques de sols argileux de plantations établies sur des terres en friche à celles des sols de plantations en milieu forestier et nous avons vérifié dans quelle mesure les différences observées affectent la croissance des arbres. Vingt plan-tations de pin gris et vingt plantations d'épinette blanche, âgées de 9 à 27 ans, ont été échantillonnées dans chaque milieu. Nos analyses indiquent que les anciens sols agricoles sont plus compacts que les sols forestiers, mais qu'ils contiennent davantage de matière organique. Malgré des différences importantes au niveau des sols, les taux de croissance de l'épinette blanche et du pin gris demeurent comparables dans les deux milieux pour la période couverte par l'étude.

Les peuplements mélangés, caractérisés par une abondance de tiges résineuses prématures croissant sous un couvert dominant de peuplier faux-tremble mature, se prêtent bien à la coupe partielle qui favoriserait la croissan-ce des tiges supprimées et l'établissement de la régénération. Dans cette étude, nous décrivons la réponse initia-le de peuplements soumis à trois types de coupe où on a fait varié l'intensité de la récolte de la surface terrière du tremble par rapport à celle des peuplements témoins. Nous avons ainsi observé que la croissance des tiges inter-médiaires d'épinette blanche était favorisée par la coupe la plus sévère seulement. Après 5 ans, les coupes n'ont pas eu d'effet sur l'établissement et la croissance de la régénération résineuse. Un essai de scarifiage visant à favoriser l'établissement de semis a donc été réalisé. À la suite d'une année semencière, le taux d'établissement des semis d'épinette blanche sur le sol scarifié variait de 125 à 165 semis/m². En dépit de la mortalité élevée d'une grande proportion des semis, une régénération adéquate pourrait être assurée dans la zone scarifiée.

Abstract:

A renewed interest in the intensive harvesting of forest biomass as a source of bioenergy in North America raises concerns about the impacts that this practice may have on the maintenance of forest soil productivity. In Canada, such concerns were first voiced in the 1970s, and studies were launched to investigate and predict the impact of intensive forest biomass removal on site productivity. Most of these studies focused on static nutrient budgets. In Canada and around the world, more detailed process models were also developed to study carbon, nitrogen and base cation cycles under different forest harvesting intensities. However, the validity of modelling results is still constrained by our lack of knowledge on the capacity of ecosystems to supply nutrients. A few sets of field trials have been established in Canada to gather empirical data on the impact of biomass removal on soil nutrient reserves as well as on tree nutrition and growth. Although still fairly recent, these field trials, along with the older ones established in other countries with similar site conditions and climates, provide opportunities to refine our understanding of the resilience of ecosystem processes and of the impacts of intensive biomass removal on ecosystem functions. Although numerous knowledge gaps and questions remain, some jurisdictions around the world have nevertheless issued policy directives and developed guidelines for biomass harvesting. As described by the concept of adaptive forest management, ecological monitoring of harvesting operations, scientific field testing and modelling can all interact to produce better knowledge that could then help improve policy directives.

Résumé:

L’intérêt renouvelé pour la récolte intensive de biomasse forestière comme source de bioénergie en Amérique du Nord soulève des inquiétudes quant aux impacts de cette pratique sur le maintien de la productivité des sols. Au Canada, ces inquiétudes ont été émises pour la première fois dans les années 1970 et des travaux de recherche ont été entrepris pour étudier et prédire les effets de la récolte de biomasse sur la productivité des sites. La plupart de ces études étaient basées sur des budgets nutritionnels statiques. Au Canada et ailleurs dans le monde, des modèles plus détaillés incluant la description des processus écologiques ont aussi été développés pour étudier les cycles du carbone, de l’azote et des cations basiques sous différentes intensités de récolte. Cependant, la validité des résultats de modélisation est toujours contrainte par notre connaissance limitée de la capacité des écosystèmes à fournir des éléments nutritifs. Quelques dispositifs expérimentaux ont été établis au Canada pour recueillir des données empiriques sur l’impact de la récolte de biomasse sur les réserves nutritionnelles du sol ainsi que sur la croissance et la nutrition des arbres. Bien que relativement récents, ces dispositifs, ainsi que des dispositifs plus anciens installés dans d’autres pays aux conditions de site et de climat semblables à celles du Canada, nous offrent l’opportunité de raffiner notre compréhension de la résilience des processus écologiques et des impacts de la récolte de biomasse sur le fonctionnement des écosystèmes. Bien que les incertitudes et les questions restent nombreuses, certaines juridictions dans le monde ont tout de même fourni un cadre politique et développé des lignes directrices pour la récolte de biomasse. Tel que décrit par le concept d’aménagement forestier adaptatif, le suivi écologique des opérations de récolte, les études sur le terrain et la modélisation peuvent interagir afin d’améliorer les connaissances scientifiques qui pourront par la suite être utilisées de façon à ajuster le cadre politique.

Soil organic matter loss and increased soil compaction have been identified as the factors most likely to directly impact tree growth in managed forests. We compared the soil quality of plantations established on former agricultural lands (n = 20) with plantations established following clear cutting of native forests (n = 20). Half of the plantations had been planted with jack pine (Pinus banksiana Lamb.) and half with white spruce [Picea glauca (Moench) Voss], 9 to 27 yr before the study. Theold field plantations had lower (at 0–10 and 10–20 cm) mineral soil macroporosity and higher field capacity than forest plantations, indicating more severe soil compaction. The old field plantations, however, also had higher soil C content, raising the permanent wilting point and canceling compaction effects on the available water holding capacity. An indicator of organic matter quality, namely the potential net mineralization per unit of soil Kjeldahl N, was lower in the old fields. Species also affected soil quality indicators—with lower values of macroporosity and higher values of field capacity observed under white spruce. Despite significant differences in soil conditions, no significant effect (P < 0.05) of plantation origin on tree growth could be found. Old fields can support productive plantations of both species.

Nous avons quantifié la réponse du tremble à l'éclaircie précommerciale (EPC) dans des conditions pro-pres au sud de l'Abitibi. Trois intensités d'éclaircie (1000, 2000, 3000 tiges/ha) ont été comparées à des peuplements témoins. La réponse initiale des peuplements ainsi que la réponse des tiges résiduelles et de la végétation concurrente à ce traitement ont été évaluées 4 ans après l'application des traitements. Suite à l'EPC, nous observons que la croissance en diamètre du tremble augmente suite à l'éclaircie mais que les trois traitements sont comparables entre eux. Les signes des maladies et les blessures aux arbres étaient rares. Malgré une mortalité élevée dans les peuplements témoins, les surfaces terrières y demeurent toujours supérieures à celles des peuplements traités. Si les tendances observées se main-tiennent, l'éclaircie précommerciale permettrait de réduire l'âge d'exploitabilité tout en augmentant le volume individuel des tiges résiduelles.

Jack pine specimens were examined for longitudinal and radial variations in selected wood quality parameters. Wood density and ring width of cross-sections were measured systematically from pith to bark along the merchantable stem using X-ray densitometry. Effects of cambial age and stem height were analyzed using a linear mixed model with two levels of nesting. A strong interaction between the two factors was found in corewood. Tree individual variation increased with cambial age for all studied wood properties and was larger in earlywood than in latewood. Radial patterns in the studied parameters closely approximated published ones in the lower stem but lessened considerably with increasing stem height. By contrast, longitudinal patterns reversed with cambial age in earlywood. High coordination was found between longitudinal patterns in corewood and radial patterns in the stem base, indicating a similar maturation pattern in the apical meristem and cambia. However, with increasing cambial age, this high coordination disappeared rapidly.

North American jack pine (Pinus banksiana Lamb.) stands are generally characterized by an even-aged structure resulting from high intensity fires (HIF). However, non-lethal fires of moderate intensity (MIF), which leave behind surviving trees, have also been reported. The objectives of this study were two-fold: (1) assess the concurrent dynamics of live trees, understory vegetation and different types of coarse woody debris (CWD) during succession after HIF; and (2) document how MIF affects stand structure component dynamics compared to HIF. Stands affected by both HIF and MIF were selected. Tree characteristics and age structure, understory biomass, and CWD volume were assessed. Our results suggest that the structural succession of jack pine stands following HIF comprises three stages: young stands (<48 years), premature and mature stands (58–100 years) and old stands (>118 years). Canopy openness and jack pine density significantly decreased with time since HIF, while black spruce density and CWD volume significantly increased. The highest structural diversity was measured in the premature and mature stands. Compared to HIF, MIF increased mean jack pine basal area, decreased average stand density, delayed the replacement of jack pine by black spruce replacement in the canopy, decreased CWD volume, and significantly increased bryophytes mass. MIF increased the diversity of live trees and generally decreased CWD structural diversity. The study confirms the diversity of natural disturbance magnitude and successional processes thereby initiated. Thereafter, it appeared to be relevant for adjustment of disturbance emulating forest-management systems. © Elsevier B.V. All rights reserved.

Abstract:

Fire can potentially have a large direct impact on tree roots and, thus, contribute to reduced vitality. Tree canopy status after fire should have an impact on the postfire production of fine roots, further affecting root function. We analyzed the standing crop of live and dead roots in Pinus sylvestris L. with varying degrees of crown scorch, 1 year after fire in northern Sweden. On the burned sites, total Pinus live fine-root biomass was 74% of that at the control sites, and it was only 19% of the control for roots <2 mm, indicating an 80% reduction due to fire. Root mortality was highest for high-scorch trees, but this was probably due to greater depth of burn in the organic soil for these trees and not to higher fire intensity per se. Fine-root production was also assessed by an ingrowth experiment. This showed relatively similar fine-root production in both control trees and fire-damaged trees, indicating a high allocation to root growth for the damaged trees, to make up for lost root function. Root dynamics after fire are related to a number of factors, and direct effects are determined by the depth of burn in the organic soil layer. Indirect, long-lasting effects could be due mainly to girdling of coarse roots close to tree stems and canopy loss. © 2008 NRC Canada.

Résumé:

Le feu peut avoir un impact direct important sur les racines des arbres et contribuer par conséquent à réduire leur vitalité. Après un feu, l’état de la canopée arborescente devrait avoir un impact sur la production de racines fines, affectant encore davantage la fonction des racines. Nous avons analysé la production existante de racines mortes et vivantes chez des tiges de Pinus sylvestris L. affectées par divers degrés de roussissement, un an après un feu dans le nord de la Suède. Dans les stations brûlées, la biomasse totale des racines fines vivantes de Pinus représentait 74 % de celle des stations témoins; dans le cas des racines <2 mm, c’était seulement 19 %, indiquant que le feu avait causé une réduction de 80 %. La mortalité des racines était la plus élevée chez les arbres avec le plus de roussissement mais cela était probablement dû à un brûlage plus en profondeur dans le sol organique pour ces arbres et non à une plus forte intensité du feu en soi. La production de racines fines a également été évaluée par une expérience de recrutement. Les résultats ont montré que la production de racines fines était relativement semblable tant chez les arbres témoins que chez les arbres endommagés par le feu, indiquant qu’il y avait une forte allocation vers la croissance des racines dans le cas des arbres endommagés pour compenser la perte de la fonction des racines. Après un feu, la dynamique des racines est reliée à plusieurs facteurs et les effets directs sont déterminés par la profondeur du brûlage dans l’horizon organique du sol. Les effets indirects de longue durée pourraient être dus principalement à l’annelage des grosses racines près du tronc des arbres et à la perte de canopée. © 2008 NRC tous droits réservés.

In the winter of 1998–1999, two partial harvesting treatments that removed 33% (1/3) and 61% (2/3) of stand basal area were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands and compared with unharvested control stands. Stands in the 1/3 treatment were low thinned, while stands in the 2/3 removal were crown thinned. Coarse woody debris dynamics were assessed during the following 6 years by means of permanent sampling plots and downed wood inventories. Between 1999 and 2004, tree mortality was, respectively, 18%, 17%, and 32% in control stands and 1/3 and 2/3 harvesting treatments. Although total snag density was similar between controls and partial cutting treatments, total snag basal area was significantly higher in controls in 2004. Between 1999 and 2004, net change in aspen snag density was positive for controls and negative for both partial cutting treatments. Partial cutting also exacerbated mortality of small-diameter white birch (Betula papyrifera Marsh.). Downed wood volume increased by 35 m3·ha–1 in controls and by 25 m3·ha–1 in the 2/3 harvesting treatment, while it decreased by 7 m3·ha–1 in the 1/3 harvesting treatment. Coarse woody debris goals can be established in silviculture prescriptions; type, timing, and intensity of partial cutting are crucial to the outcome. © 2007 NRC Canada.

À l’hiver 1998–1999, deux traitements de coupe partielle qui ont prélevé 33 % (1/3) et 61 % (2/3) de la surface terrière ont été appliqués à des peuplements équiennes de peuplier faux-tremble (Populus tremuloides Michx.) et comparés avec des peuplements témoins non traités. Les peuplements dans le traitement 1/3 ont été éclaircis par le bas tandis que les peuplements dans le traitement 2/3 ont été éclaircis par le haut. La dynamique du débris ligneux grossier a été étudiée au cours des 6 années suivant les traitements à l’aide de placettes d’échantillonnage permanentes et des inventaires du bois au sol. Entre 1999 et 2004, la mortalité arborescente a été 18 %, 17 % et 32 %, respectivement, dans les témoins et les traitements 1/3 et 2/3. Bien que les densités totales de chicots soient similaires entre les témoins et traitements de coupe partielle, la surface terrière de chicots (toutes espèces) était significativement plus élevée dans les témoins en 2004. Entre 1999 et 2004, le changement net de la densité de chicots de peuplier a été positif pour les témoins et négatif pour les deux traitements de coupe partielle. Les coupes partielles exacerbent aussi la mortalité des bouleaux à papier (Betula papyrifera Marsh.) de petits diamètres. Le volume du bois au sol a augmenté par 35 m3·ha–1 dans les témoins et par 25 m3·ha–1 dans le traitement 2/3 tandis qu’il a diminué par 7 m3·ha–1 dans le traitement 1/3. Des objectifs spécifiques quant au maintien du débris ligneux grossier peuvent être établis dans des prescriptions sylvicoles; le type, le moment et l’intensité des coupes partielles sont critiques au résultat. © 2007 NRC tous droits réservés.

Abstract

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.

Résumé

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.

Abstract : Southern boreal forests dominated by trembling aspen (Populus tremuloides Michx.) are notable for the biological richness of their plant communities. We used 12 plant community and plant functional group indicators to test the hypothesis that natural dynamics-based silvicultural systems better maintain biodiversity in aspen plant communities than conventional clear-cutting. Using CA ordination, box-and-whisker diagrams, and ANOVA, we compared the range of variability of our 12 bioindicators among five experimental stand types of the sylviculture et aménagement forestier écosystémiques (SAFE) project: mature (78 years) uncut; mature 1/3 partial-cut; mature 2/3 partial-cut; young (3 years) unburned clear-cut; young burned clear-cut; and three closely matched aspen stand types of northwest Quebec and northeast Ontario: old (105 years) uncut; young unburned clear-cut; young wildfire. Burned clearcuts partially emulated wildfires by reducing tall shrub abundance and regenerating post-fire specialists, but snags were lacking. The dual disturbance also retarded aspen regrowth and caused a 7-fold increase in non-native plants. Partial-cuts retained most attributes of mature uncut stands, but after 3 years showed little evidence of accelerating development of old stand characteristics. We concluded that SAFE natural dynamics-based silviculture better recreated the range of variability of naturally disturbed aspen plant communities than conventional clear-cutting. Improvements, including alternative burn prescriptions and snag or green tree retention in clearcuts, are nontheless warranted.© 2007 NRC Canada.

Résumé : La forêt boréale méridionale dominée par le tremble (Populus temuloides Michx.) comporte des communautés végétales remarquables par leur richesse biologique. En utilisant 12 indicateurs de communautés végétales et groupes fonctionnels de plantes, les auteurs testent l’hypothèse que des systèmes de sylviculture basés sur leurs dynamiques, assurent une meilleure biodiversité dans les communautés de tremble, que la coupe à blanc conventionnelle. En utilisant l’ordination CA, les diagrammes en boîtes à moustache (box-and-whisker) et le test ANOVA, les auteurs comparent l’amplitude de la variabilité des 12 bioindicateurs au sein des 5 types de parcelles expérimentales du projet sylviculture et aménagement forestier écosystémiques (SAFE) : mature (78 ans) non coupée; mature partiellement coupée au 1/3; mature partiellement coupée au 2/3; jeune (3 ans) coupée à blanc non brûlé; jeune coupée à blanc et brûlée. Ils ont inclus également 3 types de peuplement forestiers de tremble étroitement appariés, du nord-ouest du Québec et du nord-est de l’Ontario; suranné (105 ans) non coupé; jeune coupé à blanc non brûlé; jeune, incendié naturellement. Les peuplements coupés à blanc et incendiés se comparent à ceux issus de feux naturels avec une réduction de l’abondance de grands arbustes et en assurant la régénération par les espèces spécialistes d’après feu, mais les chicots font défaut. La double perturbation retarde également la régénération en tremble et multiplie par 7 l’arrivée d’espèces non indigènes. La coupe partielle retient la plupart des attributs des peuplements matures non coupés, mais montre peu de preuves d’un développement accéléré des caractéristiques des vieux peuplements, après 3 ans. Les auteurs concluent que l’approche SAFE, impliquant une sylviculture basée sur la dynamique naturelle, arrive mieux à recréer l’amplitude de variabilité des communautés de trembles naturellement perturbées, que la coupe à blanc conventionnelle. On obtient des améliorations certaines en incluant des prescriptions de brûlage alternatives et la rétention de chicots et d’arbres verts dans les coupes à blanc. © 2007 NRC tous droits réservés.

The effects of harvesting and slash treatments on soil nutrient dynamics were assessed in boreal aspen stands growing on mesic clayey sites. Stem-only harvested stands were compared with unharvested controls according to a complete block design with three replications. Within harvested areas, four slash treatments (stem-only harvesting [SOH], whole-tree harvesting [WHT], wood chip application, and slash burns) were compared. Treatments created a gradient of slash that ranged from 52.3 Mg ha–1 in stem-only to 13.8 Mg ha–1 in control stands. The amount of slash had no effect on wood decomposition rates but was strongly associated with higher forest floor organic C, Kjeldahl N and base cation concentrations (Cae and Mge), base saturation, pH, and effective cation exchange capacity (CEC) and lower microbial C/N when control stands were compared with stem-only harvested stands. Slash burn severity was too low to significantly reduce slash loads and induce base cation release but severe enough to reduce forest floor microbial C and N concentrations (–48 and –55%, respectively) for at least one complete growing season. Slash burn also induced increases in forest floor available P (54%) concentration compared with other slash treatments. Chipping reduced forest floor microbial N concentration by 25% and increased microbial C/N by 28% but had no impact on nutrient availability. Differences between WTH and SOH were linked to the abundance of slash. Finally, the results illustrate that whatever the treatment, the amount of slash left on the ground is the main factor found to affect soil microbial community characteristics and soil nutrient availability.

Abbreviations : CEC, effective cation exchange capacity • CHT, chipping harvesting treatment • PCA, principal component analysis • SB, slash-burn treatment • SOH, stem-only harvesting treatment • WTH, whole-tree harvesting treatment

Abstract

To assess nutrient dynamics in decomposing logs of trembling aspen (Populus tremuloides Michx.), white birch (Betula papyrifera Marsh.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.), we monitored mass losses and changes in N and P contents in dead boles from a chronosequence of sites following stand-replacing disturbances. To assess the importance of wood decomposition to nutrient cycling, we compared net estimates of nutrient release from logs with net nutrient immobilization in live-tree biomass of stands as a function of time since disturbance. Mineralization rates were 0.060, 0.053, 0.038, and 0.020 center dot year(-1) for trembling aspen, white birch, white spruce, and jack pine logs, respectively. Trembling aspen boles released large quantities of N and P during the first year of decomposition (51 kg center dot ha(-1) of N and 7 kg center dot ha(-1) of P, assuming a bole volume of 150 m(3)center ! dot ha(-1)). White birch boles acted initially as a nutrient sink and delayed the release of immobilized nutrients until a period when the stand ' s net nutrient immobilization rates were highest. Jack pine boles appeared to be intermediate in terms of their contribution as a sink or a source of nutrients but, in mature stands, provided up to 40% of N and 26% of P immobilized annually in tree biomass. As pure stands of white spruce are rare in boreal Quebec, information on nutrient accumulation in white spruce stands was not available.

Résumé

Après avoir échantillonné les débris ligneux (DL) et la matière organique du sol (MO) présents dans la couverture morte, les billes au sol et le sol minéral de surface (0–30 cm) dans 14 peuplements entre les stades intermédiaire et final de succession, établis sur une variété de types de sol et soumis à différents régimes climatiques dans le nord-ouest des États-Unis, nous avons trouvé que 44 % à 84 % du carbone (C) se retrouvait dans les DL et la MO en surface tandis que plus de 80 % de l'azote (N) se retrouvait dans le sol minéral. Dans plusieurs forêts du nord-ouest, la lutte contre les incendies de forêt et les changements naturels dans la composition des peuplements ont eu pour effet d'augmenter la quantité de DL et de MO qui peut être perdue à cause des incendies de forêt. Les peuplements qui ont des concentrations élevées de MO à la surface du sol ont plus de chances de perdre de grandes quantités de C et de N après un feu de surface de forte sévérité. Selon le guide de la qualité des sols du Service forestier américain, nous estimons que 6 % à 80 % du réservoir de C jusqu'à 30 cm dans le sol minéral pourrait être perdu lors d'un incendie considéré comme néfaste pour la productivité du sol. Ces estimations devraient varier selon le régime climatique local, la sévérité du feu dans la zone brûlée, la dimension et la classe de décomposition des DL et la répartition de la MO dans les portions organique et minérale du sol de surface. Les pertes estimées de N dues au feu étaient beaucoup plus faibles (< 1 % à 19 %). D'autres études sur la quantité et la répartition de la MO dans ces peuplements sont nécessaires pour évaluer le risque d'incendie de forêt, déterminer les impacts de différentes sévérités du feu sur les DL et les réservoirs de MO du sol ainsi que pour établir un lien entre les pertes de C et de N et la productivité des peuplements. ©2006 NRC Canada

In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage-logging (clear-cutting after fire). All 61 400-m² sampling sites were controlled for overstorey composition (Deciduous,Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem-only and Whole-tree Harvesting). Percent-cover data of vegetation and post-disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous-Mixed sites,due to the release of the understorey from Sphagnum spp.dominance, this pattern being a function of FIS. On Deciduous-Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage-logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage-logging was introduced. Salvage-logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade-tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.

The SAFE (sylviculture et aménagement forestiers écosystémique) project was set up in 1998 in the Lake Duparquet Research and Teaching Forest to test stand-level silvicultural treatments designed to reflect different aspects of natural forest dynamics. In the winter of 1998–1999, four levels of forest harvesting, including a no-harvest and a clearcut treatment, were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands according to a complete block design with three replications. Two partial cut treatments removed 33% and 61% of the stand basal area. During the first growing season, harvesting induced a large increase in indigenous understorey biomass that paralleled changes in the canopy opening. Aspen sucker density increased from 4916 stems/ha in the control to 28 751 and 63 333 stems/ha in the one-third and two-thirds harvesting treatments and 102 916 stems/ha in the clearcut. Most changes in nutrient cycling occurred in the second year and included an increase in forest floor organic C, total N, and base cation availability and a decrease in microbial C/N ratio. These changes may have occurred in response to reduced vegetation uptake and woody debris abundance.

Le projet SAFE (sylviculture et aménagement forestiers écosystémique) a débuté en 1998 dans la Forêt d'enseignement et de recherche du lac Duparquet afin de tester différents traitements sylvicoles inspirés de la dynamique naturelle des peuplements. Quatre intensités de récolte, incluant la coupe totale, la récolte de 33 et 61% de la surface terrière totale et un traitement témoin non coupé, ont été appliquées à des peuplements équiennes de tremble (Populus tremuloides Michx.) au cours de l'hiver 1998–1999, selon un plan en block complet avec trois répétitions. La végétation de sous bois a répondu par une augmentation de sa biomasse proportionnelle à l'ouverture du couvert. Au cours de la première année, la densité des drageons de tremble était de 4916 tiges/ha dans le traitement témoin, 28 751 et 63 333 tiges/ha dans les coupes partielles et 102 916 tiges/ha dans la coupe totale. La plupart des changements observés dans le cycle des nutriments sont survenus dans la couverture morte pendant la deuxième année suivant la coupe. Parmi ceux-ci figurent une augmentation du C organique, du N total et des cations basiques échangeables et une diminution du ratio C/N de la biomasse microbienne. La diminution du prélèvement par les plantes et les changements dans l'abondance des débris ligneux expliqueraient ces changements.©2004 NRC Canada

This study is a component of the Sylviculture et aménagement forestier écosystémique project, which examines ecosystem-based forest management strategies in mixedwood boreal forests. Four harvesting treatments, one no-harvest, one clearcut, and two partial cuts (33% and 61% of basal area removed), were applied to even-aged aspen stands according to a complete block design. Mountain maple (Acer spicatum Lamb.) and balsam fir (Abies balsamea (L.) Mill.) early response was examined to understand how they react to and interact with canopy opening. Only in clearcuts was maple's response (increase in growth and density) sustained and significant. Balsam fir suffered from a very slight "growth shock" 1 year after harvesting in both clear-cut and two-thirds partial-cut treatments, but growth and vigour increased with canopy opening during the next 2 years. The first year following harvesting, balsam fir growth was negatively affected by understorey aspen and mountain maple. Our results show that the two-thirds partial harvesting treatment could speed up the conversion of pure aspen stands toward mixedwood.

Cette étude s'insère dans le cadre du projet Sylviculture et aménagement forestier écosystémique qui examine les stratégies d'aménagement forestier écosystémique en forêt boréale mixte. Quatre traitements de coupe, incluant un témoin, la coupe totale et deux coupes partielles (33 % et 61 % de la surface terrière), ont été appliqués à des peuplements de tremble selon un dispositif en blocs complets. La réponse de l'érable à épis (Acer spicatum Lamb.) et du sapin baumier (Abies balsamea (L.) Mill.) a été étudiée afin de comprendre comment ces deux espèces réagissent et interagissent suite à l'ouverture du couvert. L'érable à épis n'a répondu de manière soutenue et significative (augmentation en croissance et densité) qu'à la coupe totale. Le sapin a subi un très léger « choc de croissance » l'année suivant la coupe totale et la coupe partielle deux-tiers, mais les deux années suivantes, la croissance et la vigueur de la régénération de sapin ont augmenté avec l'ouverture de la canopée. La croissance du sapin n'a été négativement affectée par la densité des rejets de tremble et d'érable à épis que la première année après la coupe. Nos résultats indiquent que la coupe partielle deux-tiers accélérerait la succession des peuplements de tremble vers une composition plus mélangée.©2004 NRC Canada

The effects of different harvest intensities, including uncut, 1/3 and 2/3 partial cuts, clearcuts with and without slash, were investigated on the germination and cumulative survivorship of white spruce and balsam fir over 2 consecutive years. We also investigated the regenerative capacity of both species on three different seedbeds across all harvest intensities. The seedbeds included were mineral, humus, and organic soil. At the germination stage, both species were strongly affected by seedbed type (p < 0.032). The germination rates of fir seeds in partial cuts were significantly greater than clearcut treatments, but spruce remained unaffected at this stage by harvest intensity. The addition of slash improved the germination rates of fir relative to the clear-cut plots without slash. The germination rates the following year were reduced on mineral soil for spruce. The cumulative survivorship at the end of the third summer still showed a significant seedbed response for both species (p < 0.007) and a significant harvest response for fir (p < 0.005). The cumulative survivorship of the second fir cohort was no longer affected by either harvest or seedbed type. Spruce, however, was still affected by seedbed type (p=0.006). The data from this study provide us with a more detailed description of the fate of cohorts recruited following a harvest operation. Still, what remains to be studied is the fate of these cohorts over the next 5–10 years.

Les effets de différentes intensités de récolte sur la germination et la survie cumulative de l'épinette blanche et du sapin baumier, incluant l'absence de coupe, la coupe partielle d'un tiers ou des deux tiers du peuplement et la coupe totale avec ou sans rémanents, ont été étudiés pendant 2 années consécutives. Nous avons aussi étudié la capacité de régénération des deux espèces sur trois lits de germination à toutes les intensités de récolte. Les trois lits de germination retenus incluaient le sol minéral, l'humus et le sol organique. Au stade de la germination, les deux espèces étaient fortement affectées (p < 0,032) par la nature du lit de germination. Le taux de germination des graines de sapin était significativement plus élevé dans les coupes partielles que dans la coupe totale mais à ce stade l'épinette n'était pas affectée par l'intensité de la récolte. L'addition de rémanents a amélioré le taux de germination du sapin comparativement aux parcelles de coupe totale sans rémanents. La deuxième année, le taux de germination de l'épinette chutait sur le sol minéral. Le taux cumulatif de survie à la fin du troisième été était toujours significativement influencé par le lit de germination chez les deux espèces (p < 0,007) et par l'intensité de la récolte dans le cas du sapin (p < 0,005). Le taux cumulatif de survie de la seconde cohorte de sapin n'était plus affecté ni par le type de récolte ni par la nature du lit de germination (p=0,006). Les résultats de cette étude nous fournissent une description plus détaillée du sort des cohortes recrutées après une opération de récolte. Il reste tout de même à étudier le sort de ces cohortes au cours des 5–10 prochaines années.©2004 NRC Canada

Parce que le bois mort fait partie intégrante des forêts, une diversité d’organismes en dépendent pour compléter leur cycle vital : mammifères, oiseaux, amphibiens, insectes, plantes vasculaires, mousses, lichens, champignons, bactéries. L’aménagement forestier réduit la quantité et la qualité du bois mort et il conduit également à une raréfaction des gros chicots et des gros débris ligneux. La raréfaction du bois mort dans les forêts aménagées peut donc réduire la biodiversité ainsi que l’emprisonnement du carbone et la fertilité des sols. Nous proposons sept mesures complémentaires permettant le maintien d’un minimum de bois mort dans les forêts aménagées du Québec, tout en évitant le gaspillage et assurant la sécurité des travailleurs forestiers.

We used a micrometeorological dispersal model to simulate seed and seedling distributions derived from subcanopy balsam fir (Abies balsamea (L.) Mill.) source trees in a trembling aspen (Populus tremuloides Michx.) dominated forest. Our first objective was to determine the effect of substituting basal area for cone production as a proxy for seed output. The results showed that the r² from the regression of predicted versus observed densities increased by similar to5% for seeds and similar to15% for seedling simulations. Our second objective was to determine the effects of changing the median horizontal wind speed. The median speed in this forest environment varies according to the proportion of leaves abscised. For values of the median expected wind speed between the extremes of leafless and full-canopy forests, the r² of predicted versus observed varied between 0.35 and 0.49 for seeds and between 0.33 and 0.62 for seedling simulations. We demonstrated that the simple one-dimensional model can have added precision if the dispersal parameters are chosen so as to allow more fine-scale variation.©2002 NRC Canada