Twenty-first century forest fires are burning so hot that the woodlands they incinerate may never come back, turning previously treed swaths of North America into open grassland, research indicates.
A study published in the journal Ecology Letters examined 1,500 sites affected by wildfire in the western United States between 1985 and 2015, comparing regrowth before and after the turn of the century. It found that the area where trees did not grow back more than doubled in the second period studied—from 15% of sites to about 33%.
Forests failed to re-establish “most frequently at lower-elevation sites that have become measurably warmer and drier in the past 30 years,” CBC News reports, citing the study’s lead author, Camille Stevens-Rumann. “Those areas may become other types of ecosystems, such as grasslands.”
Fires of unprecedented scale, strength, and persistence have scorched forests from British Columbia to southern California this year, and fire experts predict the incidence of extreme super-fires may double later this century.
“We often think about climate change as something that we’re going to feel the effects of in the future,” Stevens-Rumann told CBC News. “The truth is wildfires are facilitating those changes happening sooner. We need to just start accepting that they’re not going to become forests again, unfortunately.”
Her findings echo those of Canadian Research Chair in Integrative Ecology Merritt Turetsky. The University of Guelph ecologist examined fire sites in the Alaskan boreal where “fire was so intense that it burned up all the organic matter needed to help the soil retain nutrients and moisture required for trees to grow.”
Such incineration of the soil left the former forest “like a different planet,” Turetsky said.
In addition to permanently changing entire ecosystems—with dire implications for wildlife adapted to the vanished woodland—Stevens-Rumann noted that the permanent loss of trees has implications for the global battle to restabilize the climate. Trees that don’t grow don’t pull carbon from the atmosphere, she noted, and those that burn release it in enormous volumes.