[MCN] Tree physiology: Drought and death in forests
lance at wildrockies.org
Tue Apr 19 09:47:41 EDT 2016
PNAS Early Edition doi: 10.1073/pnas.1525678113
Meta-analysis reveals that hydraulic traits explain cross-species
patterns of drought-induced tree mortality across the globe
William R. L. Anderegg, Tamir Klein, Megan Bartlett, Lawren Sack,
Adam F. A. Pellegrini, Brendan Choat, and Steven Jansen
Drought-induced tree mortality has been observed globally and is
expected to increase under climate change scenarios, with large
potential consequences for the terrestrial carbon sink. Predicting
mortality across species is crucial for assessing the effects of
climate extremes on forest community biodiversity, composition, and
carbon sequestration. However, the physiological traits associated
with elevated risk of mortality in diverse ecosystems remain unknown,
although these traits could greatly improve understanding and
prediction of tree mortality in forests. We performed a meta-analysis
on species' mortality rates across 475 species from 33 studies around
the globe to assess which traits determine a species' mortality risk.
We found that species-specific mortality anomalies from community
mortality rate in a given drought were associated with plant
hydraulic traits. Across all species, mortality was best predicted by
a low hydraulic safety margin-the difference between typical minimum
xylem water potential and that causing xylem dysfunction-and xylem
vulnerability to embolism. Angiosperms and gymnosperms experienced
roughly equal mortality risks. Our results provide broad support for
the hypothesis that hydraulic traits capture key mechanisms
determining tree death and highlight that physiological traits can
improve vegetation model prediction of tree mortality during climate
The global climate change agreement brokered in Paris in December by
195 nations will come into effect two years earlier than originally
planned, the top United Nations climate diplomat predicted.
Even so, she said the deal had come "10 years too late," and that the
world is now at "two minutes to midnight."
"What can be said with some assurance is that there is a unique and
nearly ubiquitous compound, with the empirical formula
H(2960)O(1480)C(1480)N(16)P(1.8)S, called living matter. Its
synthesis, on an oxidized and uncarboxylated earth, is the most
intricate feat of chemical engineering ever performed - and the most
delicate operation that people have ever tampered with."
Edward S. Deevey, Jr. Mineral Cycles,
Scientific American, September 1970.
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