Southwestern wildfires are known to be fast-moving and destructive, but this summer's conflagrations astonished even veteran observers. On May 29, two cousins abandoned a campfire in a ponderosa pine forest in eastern Arizona. The resulting Wallow Fire, encouraged by dry, windy weather, burned for the next five weeks. It became the largest wildfire in the state's recorded history -- consuming 32 homes as it raced across 538,000 acres. A month later, an aspen fell across a power line southwest of Los Alamos, N.M. Overnight, the Las Conchas Fire exploded to 40,000 acres.

Five days after Las Conchas ignited, I was rattling along a dusty dirt road near the fire's northern front in a U.S. Forest Service pickup crammed with maps and backpacks. Bill Armstrong, fuels specialist program manager for the Santa Fe National Forest, was at the wheel. As we climbed into the ponderosa pines, huge clouds of gray-white smoke billowed above the mountains. Armstrong described the blaze's incredible spread. "I'd never seen fire behave that way," the 25-year agency veteran said, widening his pale-blue eyes in disbelief and shaking his head. "It confounds everything I thought I knew. That fire was up and moving before you could even get out of the way. It burned about an acre per second." By the time Las Conchas was fully contained on Aug. 2, it had burned over 156,000 acres and destroyed 63 homes -- by far the biggest fire in New Mexico's history.

Fire is, of course, vital to just about every Western ecosystem. And historically it has come in many shapes and sizes, leaving behind mosaics of green and black. Some areas remain untouched, while in others, the flames keep low to the ground, burning lightly. Elsewhere, the fire may storm through the crowns of the trees, killing many of them. Certain types of forest, like spruce-fir and mixed conifer, naturally burn in such stand-replacing fires, while drier, lower-elevation forests, like the ponderosa that covers much of the Southwest, are adapted to frequent light or moderate fires.

But as any fire ecologist will tell you, the amount and type of fuels, and the conditions that influence fire size, have changed drastically over the past century. Logging removed large trees and left flammable thickets; livestock grazing reduced the grasses that once regularly carried fires, thinning new trees and undergrowth. Meanwhile, land managers snuffed out every wildfire they could. Add climate change, which is making most of the West hotter and drier, and epidemics of tree-killing pine beetles, and conditions are prime for large, severe wildfires.

Fire activity in the West has increased sharply since the 1980s; the past 10 years have seen at least 60 fires over 100,000 acres in size. Huge fires burned in pre-settlement times, too, but today's mega-fires tend to burn more acres at a high severity. The scorched soil left behind sheds rainfall and snowmelt, causing floods that wash away topsoil and carry ash into drinking water. Large, formerly forested areas are taken over by grasses, shrubs and weeds -- species that sprout readily after fires -- and tree regrowth takes a much longer time.

For more than a decade now, the Forest Service and other federal agencies have allowed managers to make decisions based on forest health rather than expedience. They've been given permission to aggressively thin overstocked forests, whether with chainsaws or prescribed fire -- even to let some wildfires burn when they're doing ecological good.

But what's permitted on paper and what happens on the ground are often two very different things. Armstrong and other fire managers are acutely aware of how a variety of forces -- some social, some political -- conspire against progressive fire policies, and they see no easy way forward. "I'm afraid that the future of the forests of the Southwest is going to be more fires like Las Conchas and Wallow," says Armstrong. "I'm not sure how much we will be able to do to prevent those."

Armstrong's own story echoes the evolution of federal fire policy. Now 59, he grew up in a rural town near Guadalajara, Mexico, where he hunted quail and deer in the Sierra Madre. Farmers regularly burned the valley bottoms to remove crop residue and weeds, and flames sometimes crawled up into the forest. "Fire wasn't a big deal there," he says, in a voice given a gravelly edge by a lifetime of breathing smoke. " 'The woods are on fire, so what?' " He learned early on that fire had benefits: It drove his prey out into the open, and wildlife returned to burned areas as soon as they greened up. Before long, he says, he was lighting his own fires out in the Mexican woods. "I burned more acres as a kid than I've ever been able to professionally (with prescribed burns). I didn't have to worry about paperwork, air quality regulations, T&E (threatened and endangered) species. Those forests up there thrived, the impacts were positive."

He remembered those experiences when he started working with the Forest Service. "When I first came to the Carson (National Forest) in '87, there was very little burning going on. But I could see the problem, all this fuel piling up." A few years later, he moved to the Santa Fe National Forest, which allowed more burning. He came across a thesis by Craig Allen, a U.S. Geological Survey scientist, describing forest changes in the Jemez Mountains caused by long-term fire suppression. "All these little pieces clicked," says Armstrong. "My memories of Mexico, stuff I learned from studies and conferences, things I'd seen in other forests. Fire scars started to pop out at me when I was out in the woods." By the early '90s, Armstrong and most other land managers had reached the same stark conclusion: "We have a goddamn mess on our hands."