Climate change impacts on forest growth and mortality in eastern North America

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University of New Brunswick


Forests in eastern North America play a critical role in regulating global atmospheric carbon fluxes and sustaining one of the world’s largest lumber and newsprint industry. Unfortunately, tree growth and mortality are expected to be affected by climate change with temperature increases and declines in water availability. These shifts may pose a significant threat to future forest health, wood fiber supply, and carbon stock. However, the impacts of climate change on growth and background mortality remain controversial and overlooked, mainly because of limited data availability, methodological biases, and regional variability in forest dynamics. In this thesis, I compiled an unprecedented network of tree growth and mortality records from permanent sample plot network distributed across Canada and the United States, spanning a wide climatic gradient, to disentangle the climatic controls on growth and mortality. My results reveal a large, positive effect of warming on tree growth, leading to projected short-term increases in tree growth in the Canadian boreal forest, along with increases in tree mortality that may potentially cancel out some of the gains in forest productivity under climate change and affect net wood supply and carbon sequestration. Comparing the growth response to climate between overstory and understory temperate and boreal tree species, I find divergent patterns which suggest potential biases in current estimates of forest dynamics under climate change. Finally, I develop a novel, empirical approach to improve the climate-growth equations used in forest simulation models which reveals underestimated climate optimums for many species in eastern Canada. The results of this thesis, although not accounting for future changes in disturbance regimes and other forest properties such as composition or structure, should help inform forest management under climate change.