Dr. Philip Higuera has examined ancient sediments from four lakes in a remote region of Alaska in and around Gates of the Arctic National Park to determine 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 the sediment cores, Higuera and his co-authors determined that after the last ice age, the arctic tundra was very different from what it is now. Instead of being covered with grasses, herbs, and short shrubs, it was covered with vast expanses of tall birch shrubs.
This research indicates that a warming climate could make the world's arctic tundra far more susceptible to fires than previously thought. The findings are important given the potential for tundra fires to release organic carbon -- which could add significantly to the amount of greenhouse gases already blamed for global warming.
"This was a surprise," Higuera said. "Modern tundra burns so infrequently that we don't really have a good idea of how often tundra can burn. Best estimates for the most flammable tundra regions are that it burns once every 250-plus years."
The ancient sediment cores showed the shrub tundra burned as frequently as modern boreal forests in Alaska -- every 140 years on average, but with some fires spaced only 30 years apart.
Higuera's research is important because other evidence indicates that as the climate has warmed in the past 50 to 100 years, shrubs have expanded across the world's tundra regions.