Current and projected cumulative impacts of fire, drought, and insects on timber volumes across Canada

Abstract

Canada's forests are shaped by disturbances such as fire, insect outbreaks, and droughts that often overlap in time and space. The resulting cumulative disturbance risks and potential impacts on forests are generally not well accounted for by models used to predict future impacts of disturbances on forest. This study aims at projecting future cumulative effects of four main natural disturbances, fire, mountain pine beetle, spruce budworm and drought, on timber volumes across Canada's forests using an approach that accounts for potential overlap among disturbances. Available predictive models for the four natural disturbances were used to project timber volumes at risk under aggressive climate forcing up to 2100. Projections applied to the current vegetation suggest increases of volumes at risk related to fire, mountain pine beetle, and drought over time in many regions of Canada, but a decrease of the volume at risk related to spruce budworm. When disturbance effects are accumulated, important changes in volumes at risk are projected to occur as early as 2011-2041, particularly in central and eastern Canada. In our last simulation period covering 2071-2100, nearly all timber volumes in most of Canada's forest regions could be at risk of being affected by at least one of the four natural disturbances considered in our analysis, a six-fold increase relative to the baseline period (1981-2010). Tree species particularly vulnerable to specific disturbances (e.g., trembling aspen to drought) could suffer disproportionate increases in their volume at risk with potential impacts on forest composition. By 2100, estimated wood volumes not considered to be at risk could be lower than current annual timber harvests in central and eastern Canada. Current level of harvesting could thus be difficult to maintain without the implementation of adaptation measures to cope with these disturbances.

Complementarity effects are strengthened by competition intensity and global environmental change in the central boreal forests of Canada

“…Second, higher phylogenetic dissimilarity may buffer trees against the negative effects of specialist pest and pathogen outbreaks (Parker et al 2015;Grossman et al 2018). Studies have suggested that outbreaks of pests such as spruce budworm have increased in intensity in our study region (Boucher et al 2018) and regions previously inaccessible to the pest due to cold temperatures will become more susceptible as the climate warms (Pureswaran et al 2015). Further studies in areas of ongoing pestoutbreak that integrate local neighbourhood diversity and landscape-level diversity are required to determine whether the second mechanism is occurring at ecologically relevant magnitudes.…”

Atmospheric change as a driver of change in the Canadian boreal zone1

“…Insect defoliation and pathogen outbreaks might predispose weakened trees to greater vulnerability to treefall under future strong wind episodes (e.g., Taylor and MacLean 2009;Girard et al 2014;Wilson and MacLean 2015). Fire risk can also increase in tree stands previously attacked by insect defoliators (e.g., eastern spruce budworm in the southern Boreal Shield), as the accumulation of dead, vertically arranged wood structures can allow greater potential of surface fires to reach the canopy, resulting in more severe fires (Candau et al 2018; see also Boucher et al 2018).…”

Using a Trait-Based Approach to Compare Tree Species Sensitivity to Climate Change Stressors in Eastern Canada and Inform Adaptation Practices

“…In addition, forests will experience altered growing conditions due to rapid increases in temperature and shifting precipitation trends [3,4]. These stressors could result in declining forest health or increasing mortality, and potentially precipitate abrupt shifts in species composition [5][6][7]. To anticipate potential impacts of these stressors on forest ecosystems and develop corresponding adaptation strategies, forestry practitioners are increasingly using climatebased vulnerability assessments [8,9].…”