Researchers probe Arctic tree line for clues to global warming
July 31, 1996
A University of Colorado at Boulder research team will fly to
Siberia this summer to continue a long-term study on the increasing
reproductive activity by trees along portions of the Arctic tree line that
may signal greenhouse warming.
Harvey Nichols, a professor in the environmental, population and
organismic biology department, said evidence from northern Canada collected
during the past 24 years indicates dwarf spruce trees at the forest edge
have begun producing cones and pollen and may be readying to migrate into
the tundra. A research trip by Nichols last summer to Russia indicated a
similar "awakening" among dwarf spruce trees may be occurring at the
Siberian Arctic tree line.
Arctic tree line is sensitive to climatic change and is expected
to be one of the first major vegetation boundaries to register greenhouse
warming if it is indeed occurring," he said. But it will take years of
additional research to determine if the recent spruce activity is a signal
of warming triggered by a buildup of greenhouse gases in Earth's atmosphere
or just a "natural flickering" of the climate, he said.
Nichols received a $30,000 grant from the National
Geographic Society to travel to the Tiksi region of northwest Siberia in
July to collect data on dwarf spruce and larch reproduction at tree line.
He will be accompanied by CU-Boulder geography department senior Terry
McManus, EPO biology graduate student Mary Wisz and linguistics department
acting Chair Allan Taylor.
The CU research team, which also will include several Russian
ecologists, will fly to the city of Tiksi and take a chartered helicopter
to a number of sites along a 600-mile transect near the Lena River, said
Nichols. The Lena River is a massive Siberian waterway slightly smaller in
size than the Mississippi River.
The 1994 study by Nichols in the Canadian Arctic indicated dwarf
spruce trees at eight sites along an L-shaped, 930-mile transect connecting
Hudson Bay, Great Slave Lake, Great Bear Lake and the Arctic Ocean showed
increasing reproductive activity in the past two decades. Although none of
the trees were producing pollen or cones during Nichols' 1973 research
trip, trees at all eight study sites were producing both by 1993.
In addition, spruce seedlings up to six inches high were observed at several of the Canadian sites in 1993, said Nichols. The seedlings,
which were only a few feet from the parent trees, appear to have sprouted
in the mid-1980s.
"What I was seeing resembled predictions from warming scenarios,"
said Nichols. "The trees are not yet advancing, but they appear to be on
their tiptoes and in the starting blocks, readying to move into the
tundra."
Under colder conditions, spruce trees at the edge of the northern forests and in "tree islands" on the Arctic tundra reproduce asexually via
underground shoots known as clones, he said. During slightly warmer
periods, the trees reproduce sexually by forming pollen and cones that lead
to new seedlings.
The reproductive activity levels of dwarf spruce at tree line near
the Ob and Taz Rivers in north-central Siberia in 1995 was "nearly
identical" to that seen in spruce trees in the Canadian Arctic in 1993,
said Nichols. "If we find the same thing this summer in the Tiksi region,
it will be an indication that quite a substantial area of northern tree
line may be experiencing polar warming."
Dwarf spruce trees at tree line appear to periodically "turn on
and off" over the centuries in response to climate fluctuations, said
Nichols. Five thousand years ago, for example, scientists believe the
temperature at Arctic tree line was roughly 6 degrees to 7 degrees F
warmer than it is today, he said.
As they did in the Canadian Arctic, Nichols and his students will
place pollen traps in Siberian spruce groves at the edge of the forests to
monitor pollen release during the summer months. The research team also
will examine the trees visually for evidence of cone formation.
"This activity by the trees could turn off at any time," said
Nichols. "But if it keeps up and turns out to be a result of increasing
carbon dioxide in the atmosphere, then the southern edge of the tundra will
slowly fill in with trees."
Nichols said he hopes to return or to send students to both the
Siberian and Canadian Arctic regions in the coming years to monitor
reproductive changes in the trees. Funding for the project is from the
National Science Foundation, CU-Boulder and the National Geographic
Society.
Courtesy of the University of Colorado
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