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March
5, 2007 Forests of spruce
trees and
shrubs in parts of northern The boundary, or
treeline,
between forest and tundra ecosystems is a prominent landscape feature
in both "The conventional
thinking
on treeline dynamics has been that advances are very slow because
conditions
are so harsh at these high latitudes and altitudes," said Dr. Ryan
Danby,
from the Department of Biological Sciences. "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." Danby and Dr. David
Hik, also
from the Faculty of Science, reconstructed changes in the density and
altitude
of treeline forests in southwestern They found that a
rapid change in
response to climate warming during the early mid 20th century was
observed at
all locations. Treeline advanced considerably—as much as 85
metres elevation—on
warm, south-facing slopes and tree density increased
significantly—as much as
65 per cent—on cooler, north-facing slopes. "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. Widespread changes
to treelines
could have significant impacts, says Danby. As tundra habitats are lost
and
fragmented, species and habitats are forced to move upwards as well.
"The
problem is that in mountainous areas you can only go so high so they
get forced
into smaller and smaller areas," said Danby. These changes are of
particular
importance in these northern regions where First Nation people still
rely
heavily on the land, says Danby. Tundra species like caribou and sheep
populations, which are important parts of that lifestyle, have declined
across
southwestern "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, who will also be participating in an
International
Polar Year project that will be examining treeline dynamics across the
circumpolar north.
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