Climate, Forest Management Linked to Southwest Fires
When thousands of acres burned across Arizona, New Mexico and Texas last summer, firefighters and forest managers faced a more formidable foe than just smoke and flames. Research suggests that Southwestern wildfires are becoming bigger and fiercer in response to the two-headed hydra of higher temperatures and abundant fuel. In both cases, humans have a hand in creating ecosystems ready to go up in flames, but making management decisions to reverse the trend may not be so easy.
The role of snowmelt
According to one researcher, the Southwest’s most severe wildfire season on record began, not with a lightning strike or an untended campfire, but with the trickling sound of melting snow.
Anthony Westerling, an assistant professor at the University of California-Merced, explained that rising global temperatures have altered the way forests burn in the Southwest through a surprising mechanism: the timing of spring snowmelt. “Basically all the really large fires, everywhere on the map, have occurred in years of early spring snowmelt in the Southwest,” Westerling said.
Snow acts like a battery for moisture, storing rain and snow received in the wet winter months and releasing it slowly in late spring and early summer. Higher temperatures make snowpack melt earlier, and hot, dry summers begin without that extra surge of moisture.
The result: more frequent fires that cover more ground. In a 2006 Science article, Westerling describes how an abrupt transition occurred in the mid-1980s to numerous, longer-burning wildfires, according to 34 years of data from federal lands. The length of the wildfire season increased by more than two months compared to the sixteen years prior to 1986. Blazes that once required only eight days to control now burned, on average, for 37.
The 2002 Rodeo-Chediski Fire—until this year the largest on Arizona’s record—occurred in a year with early snowmelt. Westerling expects to see similar data with the 2011 Wallow Fire, which broke the 2002 record when it burned over 538,000 acres in eastern Arizona, nearly twice the size of Phoenix. The Wallow Fire destroyed 32 homes and took a month and a half to contain.
Forests filled with fuel
Westerling notes that in regions largely untouched by human management, like spruce-fir ecosystems in the Northern Rockies, the association between early snowmelt and increased fire activity is strong. But in Southwestern ponderosa pine forests, where the Wallow and La Conchos fires took place, the effects of land use policies make it difficult to tease out where the blame lies for fiercer fires.
In the early 20th century, the U.S. Forest Service began to wage war against all wildfires, including the low-lying ground fires that once thinned out small trees and swept clean the undergrowth. Suburban sprawl continues to increase the amount of land that requires vigilant fire protection. As a result, forests have become tightly packed with flammable fuels. When a spark ignites, the forest reacts like a box of fireworks. “Crown fires” rage all the way to the treetops, often razing entire ecosystems to the ground.
“These big stand-replacing fires are an anomaly, the unintended effects of fire suppression,” said Craig Allen, a research ecologist for the U.S. Geological Survey. Allen explained that ponderosa pine and conifer trees don’t easily recover from crown fires. Shrubs, grasses and small oaks quickly colonize the bare soil, leaving no room for the forest to reestablish itself.
Melissa Savage and Joy Mast, the authors of a 2005 study published in Canadian Journal for Forest Research, predict that some ponderosa pine forests in the Southwest may give way entirely to grass or shrub ecosystems—especially if crown fires continue to occur during severe droughts.
Managing for fiercer fires
Researchers often think of climate and land management as competing explanations for the increase in wildfire activity, but Westerling claims that they may complement one another in the Southwest. On longer time scales—decades and centuries—climate may be the primary driver of larger wildfires, while on shorter time scales, forest vegetation makes the most difference.
That double-edge sword makes finding a solution all the more difficult. “You can meaningfully ask, do we have a fire problem or do we have a land use problem?” said Don Falk, a professor in the School of Natural Resources and Environment at the University of Arizona, at a June briefing held by the Climate Assessment for the Southwest (CLIMAS).
Falk pointed to the Miller Fire in New Mexico as an example of how land management matters. For the last three decades, managers of the Gila National Wilderness, where no houses are at risk, have not attempted to prevent or control lightning-sparked fires. As a result, the ecosystem is “fire-adapted,” without thick underbrush or dead wood, and the Miller Fire burned in low-severity patches. Despite its extent—88,835 acres, larger than Las Vegas—the fire caused much less damage and was easier to control.
Researchers who study wildfires recommend thinning forests with controlled burns or judicious logging, but these solutions aren’t without challenges. According to Allen, “they’re things managers have the tools to do, and know how to do, but the scale of landscape that needs treatment is so big right now, and there are so few resources to do it.”
Allen also pointed out that these strategies “buy some time” but don’t address the underlying issue of a warmer, drier climate. Ultimately, he said, we need to change global energy policies if we hope to lessen the risk of fierce fires in the Southwest. “The Southwest is starting to look like the front lines of climate change in the continental U.S.,” Allen said.