September 19, 2005
Monday

ANCHORAGE, Alaska - The tundra of Alaska and northern Canada has been "greening" dramatically as the Arctic warms, with more plant growth and longer growing seasons, according to a new study that analyzed thousands of satellite images taken over two decades.

But in the vast boreal forests that stretch from Alaska's Interior into northeastern Canada, the satellites uncovered a far different outcome.

After an initial growth spurt triggered by rising temperatures and carbon dioxide concentrations, the greening of Northern forests had actually declined by 2003 - surprising the scientists conducting the survey and suggesting one factor in the surge of summer wildfires over the past few years.

The causes remain complex, but the forests appear to be drying out as the air warms up, said Scott Goetz, a senior scientist at Woods Hole Research Center in Massachusetts and one of four scientists working over the satellite data. Insect outbreaks and lack of nutrients are some other factors.

"Everyone was assuming that these forests were going to continue to green, and it turns out that there may be other factors that are causing unexpected results," Goetz said in a telephone interview. "Alaska's pretty dramatic. There's quite a gradient in the changes that we're seeing from the Interior forests of Alaska to the North Slope."

A different study examined a patch of tundra near Nome, Alaska, and found that all this new growth may be making things warmer and triggering even more growth.

Bushes that grow above the snow make the surface darker, trapping more and more of the late winter sun, accelerating heating by as much as 70 percent, said longtime Alaska snow researcher Matthew Sturm.

The two studies reached similar conclusions about tundra growth using very different tools: One spied on a continent with weather satellites, while the other intercepted sunlight a few feet above the ground in the hills northeast of Nome.

Both glimpses, from space and Earth, are part of a new research trend that monitors vegetation for evidence of climate change in the Arctic, said Sturm, with the U.S. Army Cold Regions Research and Engineering Laboratory at Fort Wainwright.

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