Shift in boreal forest has wide impact

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This stretch of boreal forest in Canada's Athabasca River valley, near Fort McMurray, Alberta burned in 2003. Scientists find that as the climate warms, vast tracks of boreal forest are undergoing a biome shift. Photo courtesy Gord McKenna/flickr

March 28, 2011

Vegetation change underway in northern forests as a result of climate change creates feedback loop that prompts more warming, scientists say.

By Douglas Fischer

Daily Climate editor

Boreal forests across the Northern hemisphere are undergoing rapid, transformative shifts as a result of a warming climate that, in some cases, is triggering feedback loops producing even more regional warming, according to several new studies.

The climate has shifted. It's done. It's clear. 
- Glenn Juday, University of Alaska, Fairbanks

Russia's boreal forest - the largest continuous expanse of forest in the world - has seen a transformation in recent years from larch to conifer trees, according to new research by University of Virginia researchers. 

In Alaska, where the larch were largely devastated by a disease outbreak in the late '90s, vast swathes of forest are becoming inhospitable to the dominant white and black spruce.

"The climate has shifted. It's done, it's clear, and the climate has become unsuitable for the growth of the boreal forest across most of the area that it currently occupies," said Glenn Juday, a forestry professor at the University of Alaska, Fairbanks.

Biome change isn't the only climate-change-related concern, either. 

fcarbon-474As warmer temperatures make the northern latitudes more accessible to development, the region's vast and pristine wetlands and peat lands are increasingly vulnerable. 

Last week the Pew Environment Group released a report calling for greater controls on development - oil and gas extraction, logging, mining, hydroelectric dams - in Canada's boreal wilderness, which contains 25 percent of the world's wetlands.

The Pew report cited a 2009 study that found Canada's boreal, if left untouched, provides $700 billion in "services" to the world annually, chiefly in carbon storage and subsistence value to First Nation peoples.

Canada is in the midst of an unprecedented drive to set aside large tracks of its boreal [TDC: July 19, 2009], but Pew's analysts said it wasn't enough. "Only a fraction has been protected to date - far less than the amount scientifically recognized as necessary to sustain the ecosystem over time," the group said in a statement.

Feedback loop

In Russia, the progression from larch to conifer is particularly troublesome, researchers say, because it will promote additional warming and vegetation change in the region.

Larch trees drop their needles in the fall, allowing the vast, snow-covered ground in winter to reflect sunlight and heat back into space and helping to keep temperatures in the region very cold. But conifers such as spruce and fir retain their needles, which absorb sunlight and increase the forest's ground-level heat retention.

This, researchers say, creates ideal conditions for the proliferation of evergreens to the detriment of larch. "What we're seeing is the system kicking into overdrive," said University of Virginia environmental sciences professor Hank Shugart in a statement. "Warming creates more warming."

Shugart is co-author of a study assessing this feedback, to be published in the journal Global Change Biology.

The researchers used a climate model to assess the impact if evergreens continued their march northward at the expense of leaf-dropping larch. The Russian boreal forest sits over a tremendous repository of carbon-rich but frozen soil. As the forest cover changes, the permafrost begins to thaw, potentially releasing huge quantities of carbon dioxide into the atmosphere, the scientist said.

"Such changes in that vast region have the potential to affect areas outside that region," said Jacquelyn Shuman, a post-doctoral researcher at the university and the study's lead author.

Devastating ice storm

In Alaska, similarly transformative changes are already underway. Shorter, drier winters and severe weather are taking a toll on the forest, Juday said. In late November, in what should be the depth of winter, Fairbanks had three days of rain that later froze, snapping limbs and downing trees. 

"You talk to people down in Canada, where the temperate forest meets the southern limit of the boreal forest, and they say that's nothing new," Juday said. "But the boreal forest is not adapted to that. (Trees) just get devastated when that happens."

Juday and co-authors at Woods Hole Research Center in Massachusetts and the University of Paris compared growth rings from trees across boreal Alaska with satellite-based estimates of forest productivity. Their study was published in the April edition of the journal Ecology Letters.

They concluded a biome shift is already underway in Alaska as higher temperatures limit forest productivity in Interior Alaska. Meanwhile in Western Alaska, where temperatures previously had been marginal for tree survival, tree growth is up, they found.

The pattern, Juday said, is "one of the first conclusively demonstrated examples of a biome shift" in response to climate change.

"It's just collapsing where it exists now and a new place exists where it can thrive," added. 

The problem, he cautioned, is that the new region is much smaller than the old.

Map of forest carbon in the Russia boreal courtesy the Distributed Active Archive Center for Biogeochemical Dynamics.

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