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Edited by Stephen W. Pacala, Princeton University, Princeton, NJ, and approved November 15, 2011 (received for review May 22, 2011)
Abstract
Forest ecosystems store approximately 45% of the carbon found in terrestrial ecosystems, but they are sensitive to climate-induced dieback. Forest die-off constitutes a large uncertainty in projections of climate impacts on terrestrial ecosystems, climate–ecosystem interactions, and carbon-cycle feedbacks. Current understanding of the physiological mechanisms mediating climate-induced forest mortality limits the ability to model or project these threshold events. We report here a direct and in situ study of the mechanisms underlying recent widespread and climate-induced trembling aspen (Populus tremuloides) forest mortality in western North America. We find substantial evidence of hydraulic failure of roots and branches linked to landscape patterns of canopy and root mortality in this species. On the contrary, we find no evidence that drought stress led to depletion of carbohydrate reserves. Our results illuminate proximate mechanisms underpinning recent aspen forest mortality and provide guidance for understanding and projecting forest die-offs under climate change.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: anderegg{at}stanford.edu.
Author contributions: W.R.A., J.A.B., L.D.L.A., and C.B.F. designed research; W.R.A. performed research; D.D.S. and J.S.S. contributed new reagents/analytic tools; W.R.A. analyzed data; and W.R.A., J.A.B., D.D.S., J.S.S., L.D.L.A., and C.B.F. 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.1107891109/-/DCSupplemental.
Freely available online through the PNAS open access option.
The roles of hydraulic and carbon stress in a widespread climate-induced forest die-off
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