Regional analyses assessing the vulnerabilities of forest ecosystems and the forest sector to climate change are key to considering the heterogeneity of climate change impacts as well as the fact that risks, opportunities, and adaptation capacities might differ regionally. Here we provide the Regional Integrated Assessment of climate change on Quebec's forests, a work that involved several research teams and focused on climate change impacts on Quebec's commercial forests and on potential adaptation solutions. Our work showed that climate change will alter several ecological processes within Quebec's forests. These changes will result in important modifications in forest landscapes. Harvest will cumulate with climate change effects to further alter future forest landscapes, which will also have consequences on wildlife habitats (including woodland caribou habitat), avian biodiversity, carbon budget, and a variety of forest landscape values for Indigenous peoples. The adaptation of the forest sector will be crucial to mitigate the impacts of climate change on forest ecosystem goods and services and improve their resilience. Moving forward, a broad range of adaptation measures, notably through reducing harvest levels, should be explored to help strike a balance among social, ecological, and economic values. We conclude that without climate adaptation, strong negative economic and ecological impacts will likely affect Quebec's forests.

Regional analyses assessing the vulnerabilities of forest ecosystems and the forest sector to climate change are key to consider the heterogeneity of climate change impacts but also the fact that risks, opportunities and adaptation capacities might differ regionally. Here we provide the Regional Integrated Assessment of climate change on Quebec’s forests, a work that involved several research teams and that focused on climate change impacts on Quebec’s commercial forests and on potential adaptation solutions. Our work showed that climate change will alter several ecological processes within Quebec’s forests. These changes will result in important modifications in forest landscapes. Harvest will cumulate with climate change effects to further alter future forest landscapes which will also have consequences on wildlife habitat (including woodland caribou habitat), avian biodiversity, carbon budget and a variety of forest landscape values for Indigenous peoples. The adaptation of the forest sector, will be crucial to mitigate the impacts of climate change on forest ecosystem goods and services and improve their resilience. Moving forward, a broad range of adaptation measures, notably through reducing harvest levels, should be explored to help strike a balance among social, ecological and economic values. We conclude that without climate adaptation strong negative economical and ecological impacts will likely affect Quebec’s forests.

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.

 

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.

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.

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.

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.

Recent Findings

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.

Summary

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.

Eastern Canadian boreal forests are mainly influenced by natural wildfires and forest management activities. To evaluate forest dynamics under possible interactions among fire and timber harvest in a future climate warming scenario (RCP 2.6, RCP 4.5 and RCP 8.5) the forest landscape model Landis II was used to simulate the dynamics of the 78000 km2 of boreal forests in eastern Canada. Forest management intensity scenarios were modeled considering the changes in the annual harvested area (0.5%, 1%, and 2%) and the age that conifers and hardwoods can be harvested (50 and 30 years, 70 and 50 years, and 90 and 70 years). The results of the 300-year model projections implied that both forest management intensity and climatic scenarios explained most of the variability in aboveground biomass, aboveground net primary productivity and forest composition. Forest management seems to be the most important factor that modified the landscape in the southern forests because there were scheduled stands with the age and composition required by each harvesting prescription to deal with the annual allowable cut volume. On the contrary, in the northern forests there was a mixed effect of climate change and forest management because many of the areas suitable for harvesting were previously burned limiting the amount of area available for harvesting. Thus, although it is expected an increase in wildfire area burned due to climate change, the intensification of forest management seems to be the most important driver of the increase of hardwoods and mixed stands and the decrease of conifers stands on the mixedwood boreal landscape, mainly in the southern forests. These results suggest that timber supply would be at risk in the Abitibi Plain, therefore, some strategies should be applied to adapt forest management to climate change.

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.

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.