More than half
of eastern U.S. tree species examined in a massive new Duke University-led
study aren't adapting to climate change as quickly or consistently as
predicted.
"Many models
have suggested that trees will migrate rapidly to higher latitudes and
elevations in response to warming temperatures, but evidence for a consistent,
climate-driven northward migration is essentially absent in this large
analysis," says James S. Clark, H.L. Blomquist Professor of Environment at
Duke's Nicholas School of the Environment.
Nearly 59 percent
of the species examined by Clark and his colleagues showed signs that their
geographic ranges are contracting from both the north and south.
Fewer species --
only about 21 percent -- appeared to be shifting northward as predicted. About 16
percent seemed to be advancing southward, and around 4 percent appeared to be
expanding in both directions.
The scientists
analyzed data on 92 species in more than 43,000 forest plots in 31 states. They
published their findings this month in the journal Global Change Biology.
The study found no
consistent evidence that population spread is greatest in areas where climate
has changed the most; nor do the species' response patterns appear to be
related to seed size or dispersal characteristics. "Warm zones have
shifted northward by up to 100 kilometers in some parts of the eastern United
States, but our results do not inspire confidence that tree populations are
tracking those changes," says Clark, who also holds appointments at Duke
as a professor of biology and statistics. "This increases the risk of
serious lags in tree migrations."
The concept of
climate-driven migration is based on the assumption that as temperatures warm,
the southern edge of some tree species' ranges could begin to erode as adult
trees die and the seeds they leave behind in the soil can no longer sprout. At
the same time, the species could spread to higher latitudes as seedlings
dispersed on their northern boundaries are able to take root in newly favorable
climates there.
To test whether
this predicted response was occurring in real life, Clark and his colleagues
pored through decades of data compiled by the U.S. Forest Service's Forest
Inventory and Analysis Program. They compared the relative distributions of
seedlings, saplings and adult trees of 92 widely distributed eastern U.S.
species at 43,334 plots in 30 different longitudinal bands, and factored in
things like seed characteristics, and changes in climate and precipitation.
"The patterns
of tree responses we were able to document using this seedling-versus-tree
analysis are more consistent with range contraction than with northward
migration, although there are signs some species are shifting to higher
elevations," Clark says.
The fact that the
majority of the northernmost latitudes documented for seedlings was lower than
those for adult trees of the same species indicates "a lack of evidence
for climate-mediated migration, and should increase concern for the risks posed
by climate change," he says.
Kai Zhu, a doctoral
student of Clark's at Duke, was lead author of the study. Christopher W.
Woodall, research forester at the U.S. Forest Service's Northern Research
Station in St. Paul, Minn., was a co-author.
The
study was funded by the National Science Foundation.
Story Source:
The above story is reprinted from materials provided by Duke University.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Kai Zhu, Christopher W. Woodall, James S. Clark. Failure to migrate: lack of tree range expansion in response to climate change. Global Change Biology, 2011; DOI:10.1111/j.1365-2486.2011.02571.x
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