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A drought-induced pervasive increase in tree mortality across Canada's boreal forests



Drought-induced tree mortality is expected to increase worldwide under projected future climate changes1,2,3,4. The Canadian boreal forests, which occupy about 30% of the boreal forests worldwide and 77% of Canada's total forested land, play a critical role in the albedo of Earth’s surface5 and in its global carbon budget6. Many of the previously reported regional-scale impacts of drought on tree mortality have affected low- and middle-latitude tropical regions2 and the temperate forests of the western United States3, but no study has examined high-latitude boreal regions with multiple species at a regional scale using long-term forest permanent sampling plots7,8,9. Here, we estimated tree mortality in natural stands throughout Canada's boreal forests using data from the permanent sampling plots and statistical models. We found that tree mortality rates increased by an overall average of 4.7% yr−1 from 1963 to 2008, with higher mortality rate increases in western regions than in eastern regions (about 4.9 and 1.9% yr−1, respectively). The water stress created by regional drought may be the dominant contributor to these widespread increases in tree mortality rates across tree species, sizes, elevations, longitudes and latitudes. Western Canada seems to have been more sensitive to drought than eastern Canada.

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Figure 1: Locations of the 96 forest PSPs in Canada's boreal forests.
Figure 2: Simulated tree mortality dynamics in Canada's boreal forests.


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Funding for this study was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) Strategic Network (ForValuenet), an NSERC discovery grant and the China QianRen programme. We thank the Forest Management Branch of Alberta Ministry of Sustainable Resource Development, Saskatchewan Renewable Resources Forestry Branch, the Forestry Branch of Manitoba, Ontario Terrestrial Assessment Program and Ministère des Ressources Naturelles et de la Faune du Québec, and our colleagues (P. Comeau, J. Liu, V. LeMay, S. Huang, J. Parton and K. Zhou) for providing detailed data. C.P. acknowledges the support he received during his sabbatical leave at Northwest A&F University, China. We also thank T. Hogg for his help with our calculations of CMI, P. J. van Mantgem for his assistance with our statistical models, W.Z. for her technical assistance and G. Hart for editorial help, as well as T. Moore, J. Guiot and P. J. van Mantgem for their comments and discussions on the earlier draft of the paper.

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C.P. contributed to the study design, data collection, method development, result analysis and writing of the manuscript. Z.M. and X.L. conducted the data analysis and developed the statistical models. All authors contributed to the data analysis, result discussion and manuscript preparation.

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Correspondence to Changhui Peng.

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Peng, C., Ma, Z., Lei, X. et al. A drought-induced pervasive increase in tree mortality across Canada's boreal forests. Nature Clim Change 1, 467–471 (2011).

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