Climate Change to Drive Trees, Forests Northward

Bears will see varied influence of changing distribution of trees.
For example, although the implications may not be perfectly clear,
polar bears will be shifting southward off the ice and onto the land
at the same time that spruce will be shifting northward, plausibly
shading the ground enough to select for or against the understory
species that might be polar bears’ future food base.

Climate Change Predicted To Drive Trees Northward

ScienceDaily (Dec. 3, 2007) – The most extensive and detailed study
to date of 130 North American tree species concludes that expected
climate change this century could shift their ranges northward by
hundreds of kilometers and shrink the ranges by more than half. The
study is by Daniel W. McKenney of the Canadian Forest Service and his
colleagues. Ranges may decrease sharply if trees cannot disperse in
altered conditions.

McKenney’s study is based on an extensive data-gathering effort and
thus more comprehensive than studies based on published range maps.
It includes data from Canada as well as from the United States.
Observations of where trees are found are used to define the “climate
envelope” of each species.

If the trees were assumed to respond to climate change by dispersing
their progeny to more favorable locations, McKenney and colleagues
found, ranges of the studied species would move northward by some 700
kilometers and decrease in size by an average of 12 percent (with
some increasing while others decreased). If the species were assumed
unable to disperse, the average expected range shift was 320
kilometers, and “drastic” range reductions of 58 percent were
projected. The authors believe that most species will probably fall
somewhere between these two extremes of ability to disperse.

The climate measures studied were chosen to represent important
gradients for plants: heat and moisture. Two climate change scenarios
were modeled. One assumed that carbon dioxide emissions would start
to decrease during the coming century, the other that they would
continue to increase. Each scenario was investigated with three
well-known models of global climate, with broadly similar results.
The authors note that their study investigated only a sample of the
700 or so tree species in North America, and that under climate
change, new species might colonize the southern part of the continent
from tropical regions. A companion article by the same authors
provides more detail about their climate envelope method as applied
to one species, the sugar maple.

This research is reported in the December issue of BioScience.

Adapted from materials provided by American Institute of Biological
Sciences, via EurekAlert!, a service of AAAS.

American Institute of Biological Sciences (2007, December 3). Climate
Change Predicted To Drive Trees Northward. ScienceDaily. Retrieved
April 24, 2008, from


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