That means the subsequent uptake of carbon on those stands “more than compensated” for the amount released in the initial fire, Walker says.
A wildfire in 2019 scorched this spruce forest in Alaska’s Kenai National Wildlife Refuge.
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But the 2007 Anaktuvuk River tundra fire, which remains the largest fire on record in Alaska’s North Slope, offers a starkly different case study. In the initial analysis there, Mack, Schuur, and their coauthors found that the fire released more than 2 million tons of carbon to the atmosphere, basically negating the amount that tundra ecosystems around the world removed from the air that year.
Subsequent studies found that more than a third of the scorched landscape sank, slid, and crumpled as the ice wedges below collapsed, the telltale signs of abrupt permafrost melting. Nearly two decades later, much of that thawed, decaying organic matter continues to release carbon dioxide and methane in the most severely burned patches of the fire scar, says Adrian Rocha, an associate professor at the University of Notre Dame.
It will take decades to centuries to recover all the carbon lost there, if ever happens at all, according to Rocha, who continues to monitor the site using Eddy covariance flux towers, which measure the exchange of greenhouse gases between Earth and atmosphere.
Mack says these on-the-ground measurements are critical to understanding what sorts of ecosystems recover, which shift into new states, whether they release a lot of carbon or a little, and when and where plant growth can offset that.
That said, the stakes of thawing permafrost are clear.
“If we step back as ecosystem ecologists, we know that there’s a lot more carbon stored below ground in permafrost than there is above ground in vegetation,” she says. “If permafrost carbon is released, it could swamp all of these other interesting details.”
In the lab
The Northern Arizona University research team shipped a pallet of soil samples back from Denali. The material included plugs of moss and decaying plant matter known as “brownies,” as well as permafrost cores and samples of the unfrozen soil layer. In the months since, they’ve cut, dried, weighed, combusted and analyzed various samples and inputted their field and lab findings into databases.
A permafrost core extracted from the Denali research plot.
JAMES TEMPLE
Walker says they’re exploring a variety of research questions, including how much that top organic layer has recovered since the initial post-fire survey and how much carbon has been lost and recovered since the fire.
