Report shows resilience of fire-damaged tundra
The Anaktuvuk River fire in 2007, the largest tundra fire in recorded history, destructively burned and ravished the tundra on Alaska's North Slope, creating a wall of smoke that was visible from 23 miles away. At the time, information on the recovery time of the tundra after wildfires was unavailable to researchers and the prospects of the damaged ecosystem looked grim.
However, scientists at the University of Alaska Fairbanks report that much of the Arctic vegetation has recovered in the North Slope tundra and that it is likely to return to its pre-fire condition within a few years. Historically speaking, tundra fires on the North Slope are rare. The Anaktuvuk River fire provided a rare opportunity for scientific research on the tundra's recovery after wildfire events.
"The most common way that wildfires start in these areas is due to lightning strikes," said Syndonia Bret-Harte, an ecosystem ecologist at the University of Alaska Fairbanks Institute of Arctic Biology. "Lightning strikes have been increasing in the region recently, and we think that it has a lot to do with climate change."
Started by a lightning strike, the Anaktuvuk River fire burned 401 square miles of tundra, was visible from outer space, and doubled the cumulative area of tundra burned in the Alaska Arctic during the past 50 years. The burned plants and soils of the land affected by the fire released 2.1 teragrams, or 2.3 million tons of carbon into the atmosphere, which is similar to the amount of carbon stored in the tundra biospheres worldwide.
"We found that about 30 years of carbon got burned away by this fire," Bret-Harte said. "So the recovery time for the tundra affected by this fire is going to be at least 30 years, if not longer."
The soil in the tundra stores an incredible amount of carbon that can be hundreds to thousands of years old. The layers of organic topsoil insulate the permafrost underneath it, which restricts fires to the above-ground plants and plant matter, leaving the majority of the carbon stored in the permafrost intact. Fire has been mostly absent in the tundra for the past 11,000 years or so, but the frequency of tundra fires have been increasing.
"If the frequency of these fires remains at long intervals, 80 to 150 years, then the tundra has time to recover," wrote Bret-Harte in the 2011 report.
However, if the fires in the tundra continue to increase, the resilience of the land will drastically decrease.?
"If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover,"she said.
In th?paper, scientists and researchers from the University of Alaska Fairbanks, including some involved in the original fire study group, began looking at the vegetation recovery rate of the tundra. The group collected plants and soils from six separate 50-meter-long tansects in areas that were unburned, moderately burned, and severely burned by the Anaktuvuk River fire. The team collected, measured and catalogued the below-ground parts of vascular plants, which include deciduous and evergreen shrubs, wildflowers and grasses, and the below-ground parts of non-vascular plants, such as lichens, moss and liverworts. The findings were optimistic in regards to the future of the tundra.
"We found that vegetation recovery was consistent with what has been observed after other tundra fires, despite the unusual severity and size of this fire," Bret-Harte said in the report. "Vegetation had not reached pre-fire levels, but had clearly begun to recover."
Climate change may be playing a large role in the tundra's recovery. Greater permafrost thaw and vegetation change are expected as climate change continues to change the tundra in the Arctic. After looking at the damage from the Anaktuvuk River fire, the authors of the new report conclude that the fire does not seem to have pushed the tundra over a tipping point and irreversibly changed the landscape.
"This fire was had an unusual size and severity compared to other fires in the tundra, but the areas underneath the tundra reacted the same way that it would in the case of smaller fires," Bret-Harte said. "What we're looking at in this area is a community of re-sprouters, and the same kind of vegetation that was there before the fire are the same ones we're seeing in the recovery. Some plants though, like lichens, take longer."
The research that Bret-Harte and her colleagues are doing is certainly important to the understanding of the tundra and the complex impact that fires can have on Arctic and sub-Arctic environments. However, it is more often than not a waiting game.
"I'd really like to go back and look at the site of that fire again, but probably in about five to 10 years from now," Bret-Harte said. "With this kind of research, it's good to wait a while."
The paper was published in the July 2013 issue of the science journal Philosophical Transactions of the Royal Society of London B: Biological Sciences and is available online at the Philosophical Transactions website.