climate studies have predicted that tree species will respond to global warming
by migrating via seed dispersal to cooler climates. But a new study of 65
different species in 31 eastern states finds evidence of a different,
of the species aren’t yet shifting their geographic distributions to higher
latitudes. Instead, they’re staying in place – but speeding up their life
University-led study, published online Wednesday in the peer-reviewed journal
Global Change Biology, is the first to show that a changing climate may have
dual impacts on forests. It adds to a growing body of evidence, including a
2011 study by the same Duke team, that climate-driven migration is occurring
much more slowly than predicted, and most plant species may not be able to
migrate fast enough to stay one step ahead of rising temperatures.
analysis reveals no consistent, large-scale northward migration is taking
place. Instead, most trees are responding through faster turnover – meaning
they are staying in place but speeding up their life cycles in response to
longer growing seasons and higher temperatures,” said James S. Clark, H.L.
Blomquist Professor of Environment at Duke’s Nicholas School of the Environment.
the impacts of this unexpected change on US forests is an important issue for
forest managers and for the nation as a whole, Clark said. It will have
far-reaching consequences for biodiversity and carbon storage.
Life cycle speeding up
whether trees are migrating northward, having faster turnover, or both, the
scientists went through decades of data on 65 dominant tree species in the 31
eastern states, compiled by the USDA Forest Service’s Forest Inventory and
Analysis program. They used computer models to analyse the temperature and
precipitation requirements of the trees at different life stages, and also
considered factors like reproductive dependence of young and adult trees.
patterns we were able to see from this massive study are consistent with
forests having faster turnover, where young trees tend to be more abundant than
adult trees in warm, wet climates. This pattern is what we would expect to see
if populations speed up their life cycle in warming climates,” said lead author
Kai Zhu, a doctoral student of Clark’s at Duke. “This is a first sign of
climate change impacts, before we see large-scale migrations. It gives a very
different picture of how trees are responding to climate change.”
that most trees are not yet showing signs of migration “should increase
awareness that there is a significant lag time in how tree species are
responding to the changing climate,” Zhu said.
was funded by the National Science Foundation (NSF), and Zhu was supported by
an NSF Doctoral Dissertation Improvement Grant.
W. Woodall, research forester at the US Forest Service’s Northern Research
Station in St Paul, Minnesota, Souparno Ghosh, a postdoctoral researcher in Duke’s
Department of Statistical Science, and Alan E. Gelfand, J.B. Duke Professor of
Statistics and Decision Sciences in Duke’s Department of Statistical Science,
were co-authors of the study. Clark also holds an appointment as professor in
the Department of Statistical Science.