What scientists are learning from wildfire in New Mexico
New Mexico's Gila National Forest is an ideal place to study wildfire scars. Ponderosa pines on the western cliffs have blackened bark at their bases. On the eastern range, frequent burns keep the grass treeless and nutrient-enriched, so that it stretches for miles like a thick green hide. From a small plane in July, I saw charred crowns swaying on the trunks of spruce and fir -- the aftermath of this summer's massive Whitewater-Baldy Fire.
The fire came after two winters of dismal snowfall left soils and vegetation extremely dry. Spring temperatures were nearly three degrees Fahrenheit above the 100-year average. In late May, lighting ignited a smoldering burn below Mogollon Baldy Peak. One week later, another fire started below Whitewater Baldy Mountain, just a short hike away. Strong winds merged the two fires, and the combined system took off like a flaming tornado. Two months later, after it was contained, 297,845 acres, 12 cabins and eight outbuildings had been burned.
Some saw this fire, the largest in New Mexico history, as a disaster. But for the scientists who convened in the Gila afterward, the Whitewater-Baldy Fire had created a perfect, landscape-scale laboratory. Over the past 40 years, wildfires in the remote reaches of the Gila have been allowed to burn more frequently than wildfires in many other national forests. This summer's wildfire gave researchers an unprecedented opportunity to observe whether more frequent use of fire can soften a blaze's impact and restore a forest to something closer to its evolutionary norm.
Research from the scientists' visit shows that large portions of the Whitewater-Baldy Fire burned less severely than other recent big fires in the Southwest, because it had less fuel powering it. It even helped portions of the forest better resist future serious fires by cleaning up undergrowth and killing smaller trees.
Larger forces, however, might yet undo decades of good work in the Gila. Scientists believe that climate change will make the Southwest hotter, drier, and more prone to pine beetle outbreaks and high-severity wildfires. Those forces might prevent burned forests from regenerating new trees.
"As time goes on, there will be a convergence of disturbances -- the adult tree seed sources are going to be dying because of beetle and drought stress and severe fires -- and then the question is whether (seedlings) can grow and survive," says Craig Allen, research ecologist for the U.S. Geological Survey.
The Gila Wilderness, which partially burned in the Whitewater-Baldy Fire, is the nation's oldest wilderness area, 558,000 acres in the middle of 3.3 million acres of national forest in southwest New Mexico. The small surrounding towns and sparse population enable forest officials to take more chances with fire.
Recognizing the necessity of fire to a healthy forest, Gila fire managers wrote one of the nation's first forest-wide fire plans in the 1970s. It allowed small wildfires to be managed for ecosystem benefits instead of being immediately stamped out. Over the next three decades, firefighters grew comfortable manipulating fire over every local district and forest type. Of that burn-savvy culture, Gabe Holguin, Gila staff fire officer, says, "It came down through the ranks. It's just a passion you have for the wilderness, and it kind of drives you to want to do the right thing."
To be sure, the Gila, like other forests, faces pressure to stamp out wildfires. Its managers followed this summer's directive from Washington, D.C., to suppress all fire starts, in hopes of keeping small fires from becoming big, expensive ones. On average, the Gila's progressive fire management suppresses 98 percent of lightning-caused fires, while the nation as a whole suppresses 99 percent. Still, that 1 percent helps Gila managers burn an average of 100,000 acres a year, plus an additional 20,000 acres from an aggressive prescription-burn program.
Out in the woods, José "Pepe" Iniguez, a Forest Service research ecologist, led me up a steep incline above Gilita Creek. We found an open ponderosa forest at the top. With other federal scientists, we hiked down into the low country, which showed little sign that the fire had even occurred. In just over a month, the grass had grown thick. The ponderosa trunks were blackened but not severely charred.
Cicadas sounded like bug zappers around us. "Could you have taken us to anything more park-like, Pepe?" Craig Allen quipped. It did indeed feel like a park, with big, widely spaced trees unhindered by brush and deadfalls. This puzzle of fire scars was an easy one to solve: Southwestern ponderosas are adapted to frequent, low-severity fires that clean up the understory. The area had burned two or three times in the last 40 years.
Preliminary conclusions suggest that the vast majority -- 87 percent -- of the Whitewater-Baldy Fire burned at low and moderate temperatures, mostly in ponderosa and mixed conifer forests, killing individual trees or small pockets without incinerating entire stands. Eighty percent of Whitewater-Baldy's total spread had burned at least once in the last century, and while solid numbers aren't yet available, researchers think that little of the forest's ponderosa pine burned at high severity. Another recent Gila fire, last year's 88,000-acre Miller Fire, burned almost exclusively in ponderosa pine forests, and only 143 acres burned at high severity. In comparison, only 40 percent of the ground covered by last year's 538,000-acre Wallow Fire in Arizona had burned in the last 100 years; about 27,000 acres of ponderosa pine burned at high severity.
At our campsite one evening, Iniguez unfolded an aerial map that charted Whitewater-Baldy's severity in minute pixels; the green and light-blue dots indicated low and moderate severity, respectively. "As (Whitewater-Baldy) came out of the Glenwood district to the east, it burned into the Bear Fire from 2006," Iniguez explained. "The fire ran into it and dropped to the ground. Then, Iron Creek -- which had burned three times -- didn't stop it, but it went from high to low severity." A more detailed map gauging the fire's precise effect on vegetation will be available next year, when it's clear which trees have survived.
Most of the high-severity patches, roughly 14 percent of the total area, were just where Iniguez expected them -- in elevations above 8,500 feet, where the spruce-fir forests historically experienced centennial stand-replacing fires. The size of those patches concerns him, though. His colleague, Ellis Margolis, from the University of Arizona's Laboratory of Tree-Ring Research, found that in the Gila, patches of spruce-fir up to 2,500 acres historically burned at high severity. Whitewater-Baldy, however, scorched up to 5,000-acre holes in the forest. Iniguez and Margolis suspect fuel buildup has created conditions that cause bigger swaths to burn.
Although the scientists drew some preliminary conclusions, more research is planned. Matt Rollins, also from the USGS, would like to compare sizes and patterns of burn patches in the high elevations with the forest's historical norms. Carol Miller, research ecologist from Missoula's Aldo Leopold Wilderness Research Institute, wonders whether a fire-resilient forest like the Gila's is also a drought-tolerant forest. Despite a desire to know more, future research here is hampered by competition over funds. Most money goes to study mechanical thinning's effects, because treatments are costly and federal administrators want to know if they're paying off.
The Gila's managers hope research will also help them encourage a more adaptable forest as the climate changes. "The Gila is a good experiment in climate change because it's a relatively healthy ecosystem, and so if you think of climate change as a disease that's coming, then the most healthy individuals should get through it a lot better," says Iniguez. But while the Gila's resilience may help it stave off some threats from climate change, it may not be able to avoid them entirely.
By lantern-light and red wine at the Snow Lake campground, after touring the burn, Allen prodded Park Williams, bioclimatologist from Los Alamos National Laboratory, about the effects of climate change on the Gila and other Southwestern forests. Allen and other scientists worry that in the future, the Southwest's forests may not recover after fires. If larger areas burn at high severity, killing all the trees for miles, the distance to seed sources may prevent new trees from sprouting. And young trees struggle to grow under drought and increased temperatures.
Earlier that day, we'd visited a mid-elevation Douglas fir site that burned in 1998; not a single new seedling had regenerated. Instead, gooseberry and grass were taking over. Williams pointed out that climate models predict average temperatures will rise two to three degrees Fahrenheit in the next 40 years, so "trees will essentially be trying to grow on a different planet." This October, he published a grim paper connecting temperature rise to moisture extraction in plants and soil, which could cause widespread tree mortality as the hot atmosphere sucks the forests dry.
Allen described what happens if, say, a tree species like ponderosa can no longer grow. "If the dominant tree species on the site can't live there climatically anymore, that whole ecosystem is going to have to reorganize. Everything's going to change," he said. So in the Gila, and in other Southwestern forests, pines may be replaced by juniper, oak or other low-elevation shrubs more tolerant of heat and drought. "This will further drive ecosystem changes in understory grasses and forbs, wildlife habitat, food webs, patterns of fire, water balances, erosion, nutrient cycling -- you name it," he later emailed.
Despite the wine, the night ended soberly.
"The Gila's not immune to climate change," said Iniguez. "The fact that there was a whole lot of low-severity (fire during the Whitewater-Baldy burn) in the low country suggests that it could come out pretty good. But the drought could just be the tip of the iceberg. It might just get worse and worse. In that case, whether you're the Gila or (any other forest), you might come out looking like another beast."