Past and future impacts of climate change on boreal forest timber supply

Abstract

The boreal forest is home to a thriving forest industry which requires stable, long term timber to remain viable. Anthropogenic climate change, caused by the release of greenhouse gasses, is occurring rapidly in northern locations. Climate change impacts the boreal forest in many different ways and has the potential impact forestry operations considerably. While there has been significant research on both climate change and the boreal forest, few studies combine both topics to include long-term timber supply. Knowledge gaps exist in terms of how ecological impacts from climate change will affect forestry, particularly in terms of net biomass, species compositions, forest disturbances and species migrations. There is also a lack of timber forecasting studies that utilize forest disturbances and implement drought mortality. Throughout this thesis, these key areas are addressed. We first conducted a literature review and synthesis of the impacts of climate change on boreal forest timber supply. We found that the disparity between migration rates of tree species with ongoing climate change may reduce the overall forest area of the boreal long term. Regional forest disturbances are increasing in frequency and intensity, affecting harvestable volumes and timber quality. Species compositions are changing; favoring early successional conifers and deciduous broadleaf species because of new local climates and more frequent disturbances. Most importantly, net biomass is likely in decline since regional increases in growth are outweighed by general increases in overall tree mortality. Our synthesis concluded that considerable reductions in the quality and quantity of boreal timber supply are likely to occur in the near future without forestry adaptation strategies or climate mitigation measures being implemented. We then simulated four climate change scenarios in three boreal forest regions to test the effect on long term timber supply and the success of two harvesting intensities. By adding annual, species specific, drought-induced tree mortality to a previously published landscape model, we sought to more completely study this important topic. Our results show long term declines in aboveground biomass, regional increases in tree mortality (from fires, insects and drought), and species composition shifts favoring broadleaf and temperate forest species. Our area-based harvesting prescriptions show that with lower harvesting intensity, consistent harvest levels area more likely to be maintained. However, our most severe climate forcing shows considerable reductions in aboveground biomass and harvested biomass. These findings necessitate action for mitigation of climate change and forestry adaptation strategies to cope with negative climate impacts. In summary, climate change considerably impacts the future success of boreal forestry. Our review of recent literature suggests that the consequences of climate change far outweigh the benefits. Our simulation results show annual biomass levels generally declines, especially in extreme future climates. Continued study and urgent management actions are needed to successfully adapt forest industry to the pressures of climate change.