Tundra fires unlock implications of a fire-driven Arctic

Kelsey Gobroski / Sun Star reporter
Aug 30, 2011

North of Fairbanks, past the Brooks Range, a swath of tundra has a few extra white heads of cottongrass and less lichen compared to its surroundings. If you dig down, as University of Florida and University of Alaska – Fairbanks (UAF) researchers did, you’d find that the soil’s burnt and thinned down past the cottongrass mounds. This place, known as Anaktuvuk River, hadn’t burned for 5,000 years. But in the summer of 2007, the largest tundra fire ever recorded tore through the area – and covered about 400 square miles. The fire got scientists thinking about what the future holds for the tundra if fires become more commonplace, and how much burning can occur before the ecosystem becomes something different.

“Usually, tundra fires – if they happen – they go out very quickly and aren’t very severe,” Donie Bret-Harte, an Institute of Arctic Biology (IAB) plant ecologist and author of a new study about the fire. For whatever reason, 2007 was different – and scientists are interested in whether this could become the norm.

When plants die and decompose, they add carbon to the permafrost-insulating organic soil layer. The layers of dead material get denser and older as you cut farther down. Fires convert all that to carbon dioxide, which floats off into the atmosphere to add to the pool of climate-shifting greenhouse gases.

Bret-Harte saw the smoke from the fire in 2007 when she was working at the IAB Toolik Field Station 24 miles south of the fire. Right away, scientists knew they needed to get funding to study this strange fire, she said. She worked with the other authors, including Michelle Mack from the University of Florida and students from both universities, to understand just how big of an impact that one fire had on the ecosystem. The journal Nature published their findings in late July.

They found that one fire fire burned just as much acreage as has burned over the tundra ecosystem for the last 60 years. It released 2,100,000,000 kilograms of carbon into the atmosphere – comparable to all the carbon the entire Arctic gathered and stored during the last 25 years.

The scientists radiocarbon dated dead moss in the soil. All of the moss had residue from nuclear bombs – meaning at most, the fire burned back the soils to what they were 50 years ago. It would take 50 years to recover what they lost. A lot, but manageable if the place doesn’t burn for another 5,000 years. Problem is, there might be more fires in the future. This study shows the potential cost of each new, unexpected fire. Anaktuvuk River was an anomaly – but it may become the new normal.

Bret-Harte compared the soil carbon reservoir to a bank account. You can take some out every now and then, but interest just isn’t going to make up for constantly withdrawing large chunks of cash.

“What you’re going to end up with is a landscape with patches…but overall the landscape will have less carbon stored than it had before,” she said.

Fires don’t just burn through the bank account of soil carbon reservoirs. They also shift back the entire ecosystem, so that life’s forced to recover in a process known as succession. First, the fire burns through the soil between clumps of grasses and sedges. Those clumps recover – right now there’s a lot of cottongrass on the sites. Eventually, you could get back to what the place looked like before the fire: grasses, sedges, patches of lichen, mosses, and so on covering the ground. Fairbanks’s ecosystem, known as the boreal forest, thrives on constant fires. The tundra also once had frequent fires — 12,000 years ago, when everything was warmer. Since then, the tundra ecosystem hasn’t worked at all like Fairbanks.

“[More frequent fires] could tip the tundra into a different regime,” Bret-Harte said. The tundra, less accustomed to burning, might get a shrubbier habitat. “It will be more like the boreal forest, but without the trees,” she said.

The information rolling in from this project didn’t conclude after the Nature article. The scientists continued working on other soil studies in the area this summer. Other scientists are looking to the fire with an interest for its long-term implications. The tundra ecosystem locks carbon in permafrost. If this ecosystem shifts to being fire-driven, the carbon gets locked in the tides of tree cycles, rather than in constant permafrost. Fires like this could shake off the supposition that the tundra is a mainstay in keeping ancient carbon from entering the atmosphere.






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