Fires will regularly rage in subarctic forest and tundra

It may be hard to imagine the land of ice and snow on fire. But research suggests that as the northern high latitudes continue warming, much of Alaska’s boreal forest and tundra will burn on a regular basis – releasing into the atmosphere the vast amounts of carbon dioxide they store.

Unlike forest and grassland ecosystems in milder climates, tundra and boreal forests – dominated by cold-loving spruce, pine and other conifers – rarely burn.

But they’re hypersensitive to changes in temperature and moisture, and as the climate warms and dries vegetation, those ecosystems will ignite much more easily, the researchers found.

According to the study, published in May in the journal Ecography, fire risk for some areas could be up to four times higher by 2100.

“We saw a significant jump,” says University of Idaho’s Adam Young, who led the study.

And with more fires come more carbon emissions: forests and grasslands that once absorbed carbon from the air, helping to reduce climate change, will release carbon instead.

Boreal forest and tundra have the most carbon to lose. These ecosystems, which comprise 33% of Earth’s land area, store 50% of the world’s soil carbon.

“The fate of these massive carbon stocks is directly tied to wildfire,” Young and his co-authors write in the Ecography study. The burns will likely amplify the loss of stores within permafrost underlying the tundra, which are already escaping as these frozen soils melt with the rise in temperature.

To understand the future of fire in Alaska’s two most dominant ecosystems, the team first looked to the past. Drawing from federal fire records, Young and his colleagues examined where wildfires occurred in Alaskan boreal forest and tundra over the past 60 years. Combining that information with climate data, they created statistical models to tease out the link between climate and fire activity during that period. Then they used those patterns, along with climate projections, to predict fire activity through to 2100.

The team found that most fires since 1950 occurred in areas with warm, dry summers. More surprisingly, Young says, they were able to identify a burn threshold – a temperature below which areas rarely burned. “You see this really distinct falloff in fire when you go below 13.4 °C,” Young says.

Given that higher latitudes are warming twice as fast as the rest of the world, Alaska is especially vulnerable to a spike in fire frequency. More than 90% of the study area, which included all of Alaska except southeastern Alaska and the Aleutian Islands, could burn more often by mid-century, the researchers found. Wildfires such as those that swept Alaska’s Noatak Preserve in 2010, scorching more than 100,000 acres of tundra, will likely become far more common. Some areas are already seeing unusual fire activity.

In the Davidson Mountains in northeastern Alaska, where average summer temperatures have reached 14.2 °C, fires increased considerably between 2000 and 2010, according to a separate recent study published in the Canadian Journal of Forest Research.

The projected rise in wildfires in Alaska is part of a global trend. Other studies suggest that wildfires will increase in other parts of the United States as well as Australia, South America, central Asia, southern Europe and southern Africa.

Young and his team hope the work can help land managers and firefighters prepare for Alaska’s fiery future. But over time, burning can cause a shift in vegetation: scorched boreal forests may give way to broadleaf species, such as aspen, which don’t burn with the same frequency.

“The forest that comes back, because it’s a novel climate, may not be the forest that was there before,” says Jeremy Littell, from the US Interior Department’s Alaska Climate Science Centre, who was not involved in the study. And if the new forest burns less often, the carbon threat may not be as great.

Scientists can speculate about how these ecosystems may respond to future climate change and fires, but no one will know for sure until that day comes. Says Littell: “Ecosystems are notorious for giving scientists and land managers surprises we weren’t counting on.”