Laura Nielsen for Frontier Scientists –
“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 information comes from Syndonia Bret-Harte, a researcher studying the fire scar left after 2007’s Anaktuvuk River fire near Alaska’s Brooks Range. The fire was devastating, larger and more severe than any tundra blaze in living memory.
The wildfire, sparked by lightning, released approximately 2.1 million metric tons [2.1 teragrams] of carbon to the atmosphere. It’s about as much greenhouse gasses as the city of Miami releases in a year. That’s a concern -plants take up carbon dioxide during photosynthesis but release it when burned. Normally the Arctic biome stores carbon: plants die and their remains become a part of frozen permafrost, releasing little carbon back into the atmosphere. But when fire burns the carbon-rich layer of peaty topsoil, carbon escapes back into the atmosphere. The Anaktuvuk River fire burned layers of soil containing plants as much as 50 years old. Another fire in the same place would access even deeper layers of soil: carbon stored for as much as thousands of years could be released into the atmosphere. The amount lost in that one fire equaled the annual carbon taken in by all living plants in the Arctic tundra biome in one year. According to the paper: “The magnitude of ecosystem C[arbon] lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening and influencing the net C[arbon] balance of the tundra biome.” That would amplify high-latitude warming - and temperatures in the Arctic are already warming twice as fast as the rest of the world.
Syndonia Bret-Harte, ecologist and plant specialist with the University of Alaska Fairbanks, and colleagues investigated the tundra’s recovery over time at the site of the 2007 Anaktuvuk River fire. Her team collected, cataloged, and assessed plant specimens from a range of areas from severely burned to unburned. They found that vascular plants (shrubs, flowers and grasses) were recovering well, while non-vascular plants (lichens and moss) were taking longer to repopulate. ‘The response of Arctic vegetation and soils following an unusually severe tundra fire’, a paper published in the Philosophical Transactions of the Royal Society B journal, chronicle her findings.
Overall, it’s heartening news. “The tundra’s clearly recovering much faster than we expected. This fire is not the big disaster people thought it would be,” said Bret-Harte. “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.” Despite the size of the burn scar, the Anaktuvuk area is following the pattern of smaller tundra burn areas which tend to regrow plant cover within 5-10 years.
What we are watching out for is the greening of the Arctic, in which plant species are shifting their ranges northward to follow the temperatures to which they are accustomed. In other high-severity tundra fires, the recovering plant ranks have been filled by deciduous shrubs and grasses instead of small lichens and mosses. Bret-Harte notes that deciduous shrub cover has been increasing in the Arctic, coinciding with anthropogenic (human-caused) warming.
According to paleorecords, ancient shrub-dominated tundra burned as often as modern-day forests do because shrub growth builds up flammable tinder. In contrast, the Arctic tundra biome has experience little fire for the last 11,000 years, since the early Holocene. Now “the frequency of tundra fires is increasing, probably as a response to climate warming," said Bret-Harte. Further south, the acreage devastated by wildfire in North America has doubled in the last 40 years.
The Anaktuvuk River fire burned 401 square miles [1,039 square kilometers] of Alaska’s North Slope. That doubled the cumulative area burned since 1950. It was the largest wildfire on record for the area. During the fire, 15 miles [24 kilometers] south at the University of Alaska Fairbanks - Institute of Arctic Biology’s Toolik Field Station, host to many scientific studies, researchers could see the wall of smoke on the horizon.
When they investigated, they measured the amount of nitrogen available in the burned soil, and found it about equal to the regional local nitrogen levels. Soil nitrogens limit plant production, since plants require nutrients like nitrogen to grow. Higher nightrogen levels mean more deciduous shrubs. The levels of nitrogen available in soil inform what plants can grow post-fire… the successional trajectory of the tundra.
Because the Arctic tundra has a carbon-rich, peaty soil, however, the ground itself is combustible, and when the fire recedes, some of the soil is gone. In a double whammy, the vulnerable permafrost is not only more exposed, but also covered by blackened ground, which absorbs more of the sun's heat and could accelerate thawing. Blackened ground also encourages formation of thunderstorms, which means more lightning strikes. It is lightning strikes that begin most wildfires in Alaska’s remote wilderness. If the huge stock of carbon stored in Arctic permafrost is released, Earth’s level of atmospheric carbon dioxide would increase drastically.
Bret-Harte reports that "If the frequency of these fires remains at long intervals, 80 to 150 years, then the tundra has time to recover… If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover."
Even setting aside the local socio-economic impacts of climate changes in Arctic communities, fires like the Anaktuvuk River fire present implications for the carbon balance of the world at large. It is good to see the vegetation there is recovering. Let’s hope that fire burn scars continue to recover as effectively.
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- ‘2007 Arctic wildfire released 50 years of stored carbon into atmosphere’ Doug O'Harra (2011) Alaska Dispatch http://www.alaskadispatch.com/article/2007-arctic-wildfire-released-50-years-stored-carbon-atmosphere
- ‘Alaska tundra shows surprising resilience after unprecedented fire’ Institute of Arctic Biology (2011)
- ‘The response of Arctic vegetation and soils following an unusually severe tundra fire’ Bret-Harte et. al. (2013) Philosophical Transactions of the Royal Society B http://rstb.royalsocietypublishing.org/content/368/1624/20120490.full
- ‘Tundra fires could accelerate climate warming’ Alisson Clark University of Florida (2011) ScienceDaily http://www.sciencedaily.com/releases/2011/07/110727131415.htm