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Quantifying Upslope Treeline Advancement in the Mountainous Areas of the Cariboo Natural Resource Region, British Columbia, from 1985 to 2020 Reimer, Amira


Upslope treeline advancement has been occurring globally over the last several decades, leading to displacement and fragmentation of alpine habitats and declines in species richness. Examining past and current treeline migration can provide insight into potential future conditions and can be used to improve ecosystem management. There is no long-term data on treeline advancement in Central British Columbia (B.C.) and the response to climate change is poorly understood. To address this, we explored treeline advancement in the Cariboo Natural Resource Region over a 35-year period (1985-2020) using Landsat imagery. Changes to the rate of advancement within the Engelmann-Spruce Subalpine Fir (ESSF) Biogeoclimatic Zone (BEC) were investigated in five-year increments using a common greenness index and the effects of slope and aspect were analysed. The most significant increase in advancement was observed between 2005 to 2015, with 190 km2 more advancement occurring in the 2010-2015 period compared to the 2005-2010 period. This large increase could be a result of temperature warming in the region beginning in the 1990s. Unexpectedly, we found steep sloped regions (> 30 degrees) exhibited greater treeline advancement throughout the study period, compared to gentle slopes (< 30 degrees). One possible reason for this is that steep slopes are less prone to cold sinks and trees favour warm temperatures for establishment. Aspect had no effect on treeline advancement, likely due to greater moisture on north-facing slopes but warmer temperatures on south-facing slopes. Additionally, significant variability throughout the study region was found, illustrating the complexity of treeline advancement and the challenges that exist when examining large geographic regions, as well as the importance of local ecosystem knowledge for future treeline modelling.

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