New Insights on Climate-Driven Extinction of Trees, Forests

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” … the paper points out that trees appear to be more suited to surviving
a cooling climate rather than a warming one. Widespread extinction is
certainly possible, as the paper points out 89 tree genera became extinct
in Europe just before the beginning of the Quaternary.”
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New discoveries about past forest changes may
help predict future ones in a changing climate
<http://news.mongabay.com/2008/0612-hance_forest_history.html>
Jeremy Hance, mongabay.com
June 12, 2008

There is no better method to understand the
future than to look to the past. Several new
studies of the earth’s glacial history are
transforming the way scientists look at tree
behavior during extreme changes in climate.
Scientists Remj Petit, Feng Sheng Hu, and
Christopher Dick described such changes in
relation to current global warming in the new
issue of the journal Science. They report that
already ” in some parts of the world, tree
species have started to shift their distributions
in response to anthropogenic climatic warming”,
thus raising the stakes for understanding how
tree species will adapt to coming changes.

Scientists have long believed that tree species
must either migrate during climate change or face
extinction. However, new fossil research has
shown that some tree populations survived
catastrophic changes in their temperatures:
evidence of small tree stands have been found
only tens of kilometers from glacier ice sheets
while others were discovered on open land north
of existing ice sheets during glacial periods.
“Thus, it appears that small populations of trees
can endure extreme climatic conditions for tens
of thousands of years,” the scientists write.
Yet, the paper points out that trees appear to be
more suited to surviving a cooling climate rather
than a warming one. Widespread extinction is
certainly possible, as the paper points out 89
tree genera became extinct in Europe just before
the beginning of the Quaternary. Using fossil and
DNA studies, scientists were able to determine
that two North American deciduous trees had the
capacity to migrate at about 100 meters per year
to survive a changing climate. Yet this will not
be fast enough if global warming predictions are
accurate: such trees would have to move
3,000-5,000 meters. These findings “[raise]
interest in the possibilities of ‘assisted
migration’⤔the translocation of populations to
areas where future climate might be favorable”.

New genetic research has also shed light on trees
ability to disperse over wide expanses. At one
time it was believed that trees pretty much stuck
to their own continent, but new research has
shown that 13,000 years ago a kapok tree species
migrated across the Atlantic Ocean from the
Neotropics to Africa. Other trees went the
opposite way. A study in Ecuador found that 21
percent of the species in a certain plot came
from long-distance dispersal, possibly Africa,
North America, the Caribbean, or somewhere else.
Such studies allow scientists to better
understand how new invasive species might take
hold in faraway places during climatic change.

While these new findings are fundamentally
changing the way scientists see the past–and
view the present–they writers caution that such
discoveries are not clear windows into the
future. The research “cannot offer a direct guide
to what we may have in stock for the future
because the combinations of climate and other
drivers (e.g., human land use) differ drastically
between the past and the future,” however they do
” provide a way to examine climate-species
relationships outside the modern realm and should
help validate ecological models for simulating
future changes”.

Rémy J. Petit, Feng Sheng Hu, and Christopher W.
Dick (2008). Forests of the Past: A Window to
Future Changes. 13 JUNE 2008 VOL 320 SCIENCE

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