Fw: [CCG] Arctic tundra vanishing much faster than predicted
---------- Forwarded Message ----------
It seems that in some cases, ecosystems change much more quickly in
response to rapid warming, than scientists predicted. The Canadian
arctic tundra is turning out to be a good example of this:
Canadian Tundra Turning Green
EDMONTON, Canada, March 6, 2007 (ENS) - Northern Canada's tundra is
disappearing at a rapid rate, with forests of spruce trees and shrubs
taking over the once frozen landscape, new research finds. The study
offers further evidence of climate change and the authors warn it
shows that the shift in the Canadian tundra can happen at a much
faster speed than scientists originally thought.
The research examines changes in the treeline between forest and
tundra ecosystems, a prominent landscape feature in both Arctic and
Scientists have long believed that the treeline will advance as global
temperatures continue to increase, but the new study shows that such a
shift will not always occur gradually.
"The conventional thinking on treeline dynamics has been that advances
are very slow because conditions are so harsh at these high latitudes
and altitudes," explained study author Ryan Danby, a biologist with
the University of Alberta. "But what our data indicates is that there
was an upslope surge of trees in response to warmer temperatures. It's
like it waited until conditions were just right and then it decided to
get up and run, not just walk."
Coniferous trees are invading the tundra, a consequence of the
changing climate. (Photo by Adrian Jones courtesy IAN)
The study, published in the "Journal of Ecology," analyzes
reconstructed changes in the density and altitude of treeline forests
in southwestern Yukon over the past three centuries.
The research team used tree rings to date the year of establishment
and death of spruce trees and reconstruct changes in treeline
vegetation. They found that a rapid change in response to climate
warming during the early mid 20th century was observed at all locations.
On warm, south-facing slopes the treeline advanced as much as 278 feet
in elevation. Tree density increased as much as 65 percent on cooler,
"The mechanism of change appears to be associated with occasional
years of extraordinarily high seed production - triggered by hot, dry
summers - followed by successive years of warm temperatures favorable
for seedling growth and survival," said Danby.
Danby noted that there is also the concern about a "positive feedback"
effect, which has been associated with the decrease in the Arctic ice
cap. As the treeline advances, he explained, the reflectance of the
land surface declines because coniferous trees absorb more sunlight
than the tundra
This light energy is then re-emitted to the atmosphere as heat, adding
to warming and further fueling the advance of the treeline.
"These results are very relevant to the current debate surrounding
climate change because they provide real evidence that vegetation
change will be quite considerable in response to future warming,
potentially transforming tundra landscapes into open spruce
woodlands," said Danby, a participant in an International Polar Year
project that will be examining treeline dynamics across the
Danby added that the shift will have adverse impacts on tundra species
such as caribou and wild sheep, which will also be forced upwards as
tundra habitats fragment and disappear.
"The problem is that in mountainous areas you can only go so high so
they get forced into smaller and smaller areas," said Danby.
Danby added that the changes are of particular importance in these
northern regions where indigenous people still rely heavily on the land.
Caribou and sheep populations have already declined across
southwestern Yukon, he said. cr.middlebury.edu