Study Of Ancient Pollen Shows That Shrubbier, Warmer Tundra Burned More Often Than Thought

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A study of ancient pollen grains found in Arctic sediments has revealed that the tundra present before the last ice age was more shrubby and burned more often than previously thought. The finding has implications for today’s tundra, which appears to be increasing in shrub density as global temperatures rise and could undergo more frequent forest fires in the future.

"Increased burning in tundra ecosystems is significant because it has the potential to release stored organic carbon to the atmosphere," Philip Higuera of Montana State University, US, told environmentalresearchweb, "both directly, by burning, and indirectly, by melting permafrost and facilitating vegetation change, which would, in turn, amplify carbon dioxide-induced climate change. Feedbacks between increased temperatures and ongoing warming are a major source of uncertainty when predicting the ultimate consequences of climate change on arctic and global systems."

Higuera and colleagues from the University of Washington, Lawrence Livermore National Laboratory, Montana State University and the University of Illinois, all in the US, examined fossilized pollen grains from sediments taken from four lakes in a remote region of Alaska, near the gates of the Arctic National Park. The pollen revealed that tundra in the region from 14,000 to 10,000 years ago was dominated by tall birch shrubs. In contrast, tundra in the area today contains grasses, herbs and short shrubs. Charcoal in the sediments also indicated frequent burning of the vegetation.

"Our findings provide precedence for tundra ecosystems sustaining 'frequent' fires, where 'frequent' is one fire every 140 years, on average," said Higuera. "The ability for tundra to burn at this rate was previously unknown. We infer that frequent fires were made possible by (a) the nature of the tundra vegetation (i.e. dense shrubs), and (b) dry moisture conditions."

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http://environmentalresearchweb.org/cws/article/research/33511