Impacts of drought-induced forest mortality on Canadian boreal forest carbon sinks

Background/Question/Methods

The boreal forests, identified as a critical “tipping element” of the Earth’s climate system, play a critical role in the global carbon budget. Recent findings have suggested that terrestrial carbon sinks in northern high-latitude regions are weakening, but there has been little observational evidence to support the idea of a reduction of carbon sinks in northern terrestrial ecosystems. In this study, we estimated tree mortality in natural stands throughout Canada's boreal forests using data from the using data from long-term forest permanent sampling plots and statistical models, and then estimated changes in the biomass carbon sink of natural stands throughout Canada's boreal forests.

Results/Conclusions

We found that tree mortality rates increased by an overall average of 4.7% per year from 1963 to 2008, with higher mortality rate increases in western regions than in eastern regions (about 4.9 and 1.9% per year, respectively). We found that in recent decades, the rate of biomass change decreased significantly in western Canada (Alberta, Saskatchewan, and Manitoba), but there was no significant trend for eastern Canada (Ontario and Quebec). Our results revealed that recent climate change, and especially drought-induced tree mortality ( due to water stress), is the dominant cause of the observed reduction in the biomass carbon sink, suggesting that western Canada's boreal forests may become net carbon sources if the climate change–induced drought continues to intensify.