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Boreal forests, vital carbon sinks storing about 32% of the world's forest carbon, face significant threats from climate change. In west-central Canada, studies have primarily focused on the impacts of forest fires and water availability on forest biomass. However, the effects of rising atmospheric CO2 and climate warming, particularly in relation to spatial variations in mean annual temperature (MAT), remain less understood. Our comprehensive study utilizes data from 871 permanent sample plots, encompassing 208,961 trees across western boreal forests of Canada over 50 years. Our findings reveal a net biomass increase of 0.052 Mg ha-1 yr-1 per degree increase in plot MAT. Two-thirds of this increase can be attributed to reduced mortality rates at higher MATs. Notably, warmer regions showed a more pronounced decrease in growth with stand age, suggesting that younger forests might benefit more from climate warming compared to mature ones. We identified a MAT threshold of 3 °C, beyond which forests show net biomass increase with rising CO2, while colder forests exhibit a decline. Future projections indicate that net biomass change in northeastern regions in our study area, particularly above 56° N, may experience adverse effects from increasing CO2 levels, while southwestern regions could benefit. Besides, in some regions south of 52°N under the 2041–2070 SSP5–8.5 scenario, where predicted temperatures exceed historical maximums, the potential instability and unpredictability of biomass-climate-CO2 relationships under such extreme conditions should be noted. Our study underscores the complex interplay between climate change factors and boreal forest biomass, highlighting the need for tailored forestry management strategies that consider these spatial and dynamic patterns.
Xu et al. (Fri,) studied this question.