Effects of aridity on the demography, distribution, and biomass of trees and forests in western Canada

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Recent observations indicate that increasing drought and water stress will be major drivers of forest responses to global climate change. This forecast appears to be particularly true for boreal forests of western Canada, where drought-related increases in tree mortality and moisture-limited growth and recruitment rates confirm that forest dynamics are tightly coupled with water availability. Yet, despite good empirical evidence for the effects of water stress in western forests, ecologists have a limited understanding of how impacts of increasing aridity on tree-level demography (i.e., growth, mortality, and regeneration) could translate to broader changes in the geographic distribution and standing biomass of forest biomes. I plan to undertake a coordinated set of field studies and modelling experiments to quantify how forests in western Canada will respond to increased water stress over the next century. This research program will test hypotheses regarding: (1) how tree mortality and recruitment vary with water availability; (2) how moisture-related demographic variation governs the distribution and standing biomass of western boreal forests; and (3) how this forest region may respond to future aridity. Firstly, I will use an Unmanned Aerial Vehicle to collect very high resolution 3D imagery of forest landscapes in the Cypress Hills region; these data will be used to quantify spatial and temporal variation in canopy tree mortality across elevational gradients in precipitation and soil moisture. Secondly, I will establish and re-census a set of permanent forest plots to determine the effects of light and water on juvenile tree dynamics under different levels of canopy closure. Thirdly, I will use aerial and plot-based demographic data to parameterize an individual-based model of forest dynamics that can simulate how the regional distribution and abundance of tree species vary across climate gradients and with forest age. By integrating data and results from field studies into a dynamic forest model, this research will produce well-grounded, quantitative predictions of how climate-related demographic variation could lead to future changes in forest cover, species composition, and carbon storage in western Canada. Findings from this research will ultimately lead to better representations of demographic processes in models of the global terrestrial carbon cycle, and will enable more robust projections of vegetation dynamics under environmental change. These advances will be valuable to Canadian and international policy makers seeking to either mitigate or adapt to climate change impacts on forest ecosystem services.