Droughts are increasing tree mortality and declining carbon sink of Canadian boreal forests from 1970 to 2020

Background/Question/Methods

Global-change-type droughts are expected to iensify and become more frequent this century as a result of climate change. The Canadian boreal forests, which occupy about 30% of global boreal forests, have been identified as a critical “tipping element” of the Earth’s climate system, and play a critical role in the global carbon budget. However, little is known about the spatio-temporal changes in drought-induced tree mortality and its impacts on biomass carbon dynamics of the entire Canadian boreal forests.Here, we quantified spatio-temporal changes in drought-induced tree mortality rate and its impacts on the biomass carbon sink throughout Canada’s boreal forests over the period of 1970-2020 using a drought-induced tree mortality model of TRIPLEX-Mortality.

Results/Conclusions

We found that around 43% of Canadian boreal forests (71% located in the western region) experienced a significant increased trend in mortality with an acceleration for this increased mortality trend of the entire Canadian boreal forest after 2002. This increased drought-induced tree mortality resulted in significant carbon loss across Canada's boreal forests. With more frequent droughts expected in the future, Canadian boreal forests may lose their role as a strong sink of carbon, leading to significant positive climate feedback and exacerbating warming trends.