Warming climate may cause arctic tundra to burn

Warming climate may cause arctic tundra toburn

5 March 2008

published by www.enn.com

Global —  Research from ancient sediment cores indicates that a warmingclimate could make the world’s arctic tundra far more susceptible to firesthan previously thought. The findings, published this week in the online journal,PLoS ONE, are important given the potential for tundra fires to release organiccarbon — which could add significantly to the amount of greenhouse gasesalready blamed for global warming.

Montana State University post-doctoral researcher Philip Higuera is the leadauthor on the paper, which summarizes a portion of a four-year study funded bythe National Science Foundation.

Higuera and his co-authors examined ancient sediments from four lakes in aremote region of Alaska in and around Gates of the Arctic National Park todetermine what kind of vegetation existed in the area after the last ice age,14,000 to 9,000 years ago. By looking at fossilized pollen grains in thesediment cores, Higuera and his co-authors determined that after the last iceage, the arctic tundra was very different from what it is now. Instead of beingcovered with grasses, herbs, and short shrubs, it was covered with vast expansesof tall birch shrubs.

Charcoal preserved in the sediment cores also showed evidence that thoseshrub expanses burned — frequently.

“This was a surprise,” Higuera said. “Modern tundra burns soinfrequently that we don’t really have a good idea of how often tundra canburn. Best estimates for the most flammable tundra regions are that it burnsonce every 250-plus years.”

The ancient sediment cores showed the shrub tundra burned as frequently asmodern boreal forests in Alaska — every 140 years on average, but with somefires spaced only 30 years apart.

Higuera’s research is important because other evidence indicates that asthe climate has warmed in the past 50 to 100 years, shrubs have expanded acrossthe world’s tundra regions.

“There is evidence of increasing shrub biomass in modern tundra ecosystems,and we expect temperatures to continue to increase and overall moisture levelsto decrease. Combine these two factors and it suggests a greater potential forfires,” Higuera said. “The sediment cores indicate that it’s happenedbefore.”

The world’s high latitude tundra and boreal forest ecosystems containroughly 30 percent of the planet’s total soil carbon. Currently, much of thecarbon is locked in permafrost. But a warming climate could cause the permafrostto melt and release its carbon stores into the atmosphere where it wouldcontribute to the greenhouse effect.

“Vegetation change through an increase in shrub biomass and more frequentburning will change a great deal of the carbon cycle in these high latitudes,”Higuera said. “We don’t fully understand the implications, except thatit’s reasonable to expect that carbon that was previously locked up couldenter the atmosphere.”

The paper is the first in a series Higuera expects to publish from his fieldwork. Future papers will examine how climate, vegetation, and fire regimes haveinteracted over the past 15,000 years in the region.

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