ANCHORAGE, Alaska, Nov 13, 2015 – Large and severe tundra fires cause top down permafrost thaw, playing a major role in altering Arctic landscapes according to a new study led by the U.S. Geological Survey. 

The study documented widespread thermokarst formation, characterized by subsidence of the land surface as a result of melted ground-ice, in the years following a tundra fire event. Thaw of ice-rich permafrost is known to impact terrestrial and aquatic ecosystems by altering vegetation communities and hydrology as well as releasing carbon that was previously stored in the frozen ground below.   

"Thermokarst development may sound like an esoteric topic, but when ground ice melts it affects everything at the surface, formation or drainage of lakes, how much water runs off the landscape and what kind of plants can grow," said Philip Martin, Science Coordinator for the Arctic Landscape Conservation Cooperative. "This is an essential part of the puzzle for resource managers and Arctic residents to piece together how the land is changing." 

Researchers, led by the USGS, used repeat airborne LiDAR data acquisitions, a remote sensing tool that allows for the creation of highly detailed topographic models of the landscape, to quantify thermokarst development in the aftermath of the 2007 Anaktuvuk River tundra fire. By comparing data obtained two and again seven years post-fire, researchers determined that thermokarst affected more than 34 percent of the studied burned tundra area compared to less than one percent in similar unburned tundra. 

Arctic tundra fires are known to have an immediate and severe impact on the landscape through combustion of vegetation and soil organic layers. However, widespread thermokarst development in the aftermath of an Arctic tundra fire had not been previously measured in detail. 

"With LiDAR data acquisitions, we are able to document landscape changes in a measurable way like never before," said lead author Benjamin Jones, a Research Geographer with the USGS. "It is likely that the impact of fires and other disturbances on permafrost-influenced terrain in the Arctic has been underestimated since highly precise elevation data, such as from LiDAR datasets, are not widely available in these regions."

The paper " Recent Arctic tundra fire initiates widespread thermokarst development" was published in the journal Scientific Reports, the online open access journal from the publishers of Nature.

The work was supported by the Land Change Science and Land Remote Sensing programs at the USGS, the USGS Alaska Science Center, the Arctic Landscape Conservation Cooperative, the University of Alaska Fairbanks, and the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research.  

A photo from the study area acquired in August 2015 showing thermokarst development manifest as a network of troughs forming over degrading ice wedges (left). Comparison between the two airborne LiDAR data showing permafrost terrain subsidence in the aftermath of a large and severe Arctic tundra fire. (High resolution image)

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