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Regional drought-induced reduction in the biomass carbon sink of Canada's boreal forests
Edited by Steven C. Wofsy, Harvard University, Cambridge, MA, and approved December 28, 2011 (received for review July 18, 2011)

Abstract
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. Here, we estimated changes in the biomass carbon sink of natural stands throughout Canada's boreal forests using data from long-term forest permanent sampling plots. 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 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 droughts continue to intensify.
- global warming
- forest aboveground biomass
- drought index
- northern hemisphere carbon uptake
- positive feedback
Footnotes
↵1Z.M. and C.P. contributed equally to this work.
- ↵2To whom correspondence should be addressed. E-mail: peng.changhui{at}uqam.ca.
Author contributions: Z.M. and C.P. designed research; Z.M. and C.P. performed research; Z.M. and C.P. contributed new reagents/analytic tools; Z.M., C.P., Q.Z., H.C., G.Y., W.L., X.Z., W.W., and W.Z. analyzed data; and Z.M. and C.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1111576109/-/DCSupplemental.
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