[MCN] How sustainable are Southeast US forests?

[Lance Olsen]

Drought implicated in slow death of trees in southeast's forests
DUKE UNIVERSITY
Public Release: 19-Aug-2015

Damage suffered by trees during a drought can 
reduce their long-term survival for up to a 
decade after the drought ends, a new study of 
tree mortality in southeastern forests finds. By 
identifying the symptoms that mark a tree for 
later death and the species that are at highest 
risk, the study's findings may give managers and 
scientists a way to recognize and reverse 
drought-induced declines before it's too late.

Aaron Baird Berdanier and James S. Clark In 
press. Multi-year drought-induced morbidity 
preceding tree death in Southeastern US forests. 
Ecological Applications. 
http://dx.doi.org/10.1890/15-0274.1

Multi-year drought-induced morbidity preceding 
tree death in Southeastern US forests
Aaron Baird Berdanier1,* and James S. Clark2
1Duke University
2Duke University, Nicholas School of the Environment

Recent forest diebacks combined with threats of 
future drought focus attention on the extent to 
which tree death is caused by catastrophic events 
as opposed to chronic declines in health that 
accumulate over years. While recent attention has 
focused on large-scale diebacks, there is concern 
that increasing drought stress and chronic 
morbidity may have pervasive impacts on forest 
composition in many regions. Here we use 
long-term, whole-stand inventory data from 
Southeastern US forests to show that trees 
exposed to drought experience multi-year declines 
in growth prior to mortality. Following a severe, 
multi-year drought, 72% of trees that did not 
recover their pre-drought growth rates died 
within 10 years. This pattern was mediated by 
local moisture availability. As an index of 
morbidity prior to death, we calculated the 
difference in cumulative growth after drought 
relative to surviving conspecifics. The strength 
of drought-induced morbidity varied among species 
and was correlated with drought tolerance. These 
findings support the ability of trees to avoid 
death during drought events but indicate shifts 
that could occur over decades. Tree mortality 
following drought is predictable in these 
ecosystems based on growth declines, highlighting 
an opportunity to address multi-year 
drought-induced morbidity in models, experiments, 
and management decisions.

*To whom correspondence should be addressed. E-mail: aaron.berdanier at gmail.com
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"Here, we examine the physiological basis of a 
recent multiyear widespread die-off of trembling 
aspen (Populus tremuloides) across much of 
western North America. Š.  We test whether 
accumulated hydraulic damage can predict the 
probability of tree survival over 2 years. We 
find that hydraulic damage persisted and 
increased in dying trees over multiple years and 
exhibited few signs of repair  Š.  Contrary to 
the expectation that surviving trees have 
weathered severe drought, the hydraulic 
deterioration demonstrated here reveals that 
surviving regions of these forests are actually 
more vulnerable to future droughts due to 
accumulated xylem damage."

WILLIAM R. L. ANDEREGG et al. Drought's legacy: 
multiyear hydraulic deterioration underlies 
widespread aspen forest die-off and portends 
increased future risk. Global Change Biology 
(2013) 19, 1188-1196, doi: 10.1111/gcb.12100

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