Arctic tundra fires may increase significantly as a result of continued global warming, warns a new study examining the relationship between historic changes in climate, vegetation, and wildfires in Alaska.
And as about a third of the world鈥檚 soil-based carbon is locked in high-latitude tundra and boreal forest ecosystems, the release of carbon dioxide from an increase in burning tundra could also play a significant role in fuelling further warming, the study鈥檚 authors add.
Warming temperatures may increase the amount of vegetation available to burn, by prompting a shift from tundra comprising mainly of small herbs and grasses to shrub tundra, suggests the study.
Advertisement
鈥淎s the climate changes, biomass will increase in the tundra and with it will come more fires,鈥� explains of Montana State University in Bozeman, US. With more plant matter available to burn, plus a drier climate due to warming, the risk of fires increases.
Burning bushes
Higuera and colleagues collected core samples from the bottom of four lakes along the southern slope of northern Alaska鈥檚 .
By radiocarbon dating the samples and teasing out fossilised pollen grains from within the sediment, they were able to piece together the exact plant communities that existed in the region at the end of the last Ice Age, from 14,000 to 9000 years ago.
At the beginning of the period, vegetation on the southern slope was much like the herbs, grasses and low lying shrubs found in tundra ecosystems north of the Brooks Range today.
But starting 10,000 years ago, they found shrub tundra 鈥� tall birch shrubs that are likely to have grown up to 2 metres in height 鈥� predominating. Charcoal fragments found within the sediment suggest that this denser tundra burned every 140 years on average, nearly twice as often as tundra is believed to burn in Alaska today.
Expected warming
Higuera鈥檚 sample sites slowly changed from tundra to shrub tundra to boreal forest as the region warmed after the last Ice Age. Meanwhile, Alaska鈥檚 North Slope, the area starting just north of the Brooks Range, has remained low-lying herb tundra to date.
However, as the region鈥檚 climate is anticipated to (PDF) , tundra north of the Brooks Range will likely become shrub tundra in the near future.
鈥淚f current rates are maintained, we would expect 100% of tundra in northern Alaska to be dominated by shrubs in another century,鈥� Higuera says, adding that the boreal forests may also intrude further north as well.
of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole, Massachusetts, US, applauds the study, but notes that the drying out of tundra vegetation as a result of a warming climate may already be causing an increase in fires.
More than 350 square miles of tundra north of the Brooks Range burned in summer 2007, more than has burned in the region in the last 50 years combined according to Shaver. 鈥淚f we have more warm, dry summers, I wouldn鈥檛 be surprised if we have a lot more fires on the North Slope,鈥� he says.
Journal reference: (DOI: 10.1371/journal.pone.0001744)
Climate Change 鈥� Want to know more about global warming: the science, impacts and political debate? Visit our continually updated special report.
