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Abstract

Climate change is impacting the stability and livelihoods of northern communities across Canada. Warming is accelerated at high-latitudes which has cascading effects on permafrost, hydrology, vegetation and carbon storage. The transitional area between the boreal and tundra biomes, known as the “forest-tundra ecotone”, is a large, dynamic region of climate-sensitive vegetation, including forests, tall-shrubs and tundra plant communities. Warming temperatures are expected to release reproductive limitations on trees facilitating northward advance of the boreal biome. However, there is significant variation in measurements of treeline advance across different locations, and the timing of advance relative to recent climatic changes are unclear. The primary objective of my dissertation is to use remote sensing datasets to investigate change in vegetation structure and its implications for carbon storage across the Canadian forest-tundra ecotone. To accomplish this, I used spaceborne light detection and ranging (Lidar) measurements and multi-spectral satellite imagery to model vegetation structure across 180 million hectares of northern Canada. These models were used to evaluate whether change in vegetation structure over the past 40-years is consistent with northward advance of the boreal biome. I found that forested area expanded northward by approximately 1 million hectares across Canada, but large parts of the limit were stable over time. Mean annual temperature and total precipitation also increased along the forest limit, indicating that the position of the forest-tundra boundary is out of equilibrium with recent climate warming. A central theme of this dissertation is assessing change across spatial and temporal scales. To this end, I also used high-resolution drone imagery to link fine-scale vegetation structure with measurements of soil organic carbon across northern tree and shrublines. At the regional scale, I paired historic air photos with contemporary satellite imagery to assess long-term patterns in tree and shrub expansion at multiple treeline sites. These patterns were linked back to national mapping products derived from multi-spectral time series to understand potential biases and evaluate strengths in both approaches. Ultimately, this dissertation provides new insights into climate driven impacts on northern vegetation across Canada, and demonstrates the use of novel remotely sensed data to support future research.