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Burned Ponderosas Unlikely To Regrow

DOME ROAD, SANTA FE NATIONAL FOREST – This Jemez Mountains landscape – twice logged, twice burned – may never again see ponderosa forests.

“This was wall-to-wall trees,” said U.S. Geological Survey ecologist Craig Allen as he surveyed miles of mesa-top landscape literally burned to the ground. Loggers came through twice to cut the big stuff. The Dome Fire in 1996 took some of what remained. And then June 26, the Las Conchas Fire blazed through a 50-square-mile patch where now the only signs of movement are gray ashen dust devils.

Fire left “ghost logs” scattered across the landscape, lines of white ash that are all that remains of logs laying on the mesa when Las Conchas blew through.

For miles along the St. Peter’s Dome Road, there are no birds.

“There’s barely even insects,” Allen pointed out.

After the Dome Fire destroyed the forest, the big pines were replaced by low, shrubby plants, Gambel oak and other similar species.

A few patches of ponderosa were left, which had the potential to provide seed for a slowly regrowing forest. But those trees burned in Las Conchas.

The result is a patch denuded of ponderosa so vast that there is no ponderosa left to provide the nursery stock for a new forest.

The only bits of green are tiny shoots of shrubby Gambel oak and New Mexico locust here and there, plants burned to the ground but returning from still-living roots after summer rains.

“Shrubs own this,” Allen said of the mesa that was once “wall-to-wall trees.”

As fires burn through Southwestern forests with increasing intensity, the ponderosa pines so characteristic of the landscape are increasingly being eaten away, and in some areas have little chance of returning, scientists say.

Las Conchas was the sixth and largest of a series of increasingly destructive fires dating to the 1950s on the east side of the Jemez Mountains. While some of the fire burned at low severity, leaving healthy forests behind, more than 150 square miles of the area’s forests have been burned in destructive, stand-replacing fires, according to Allen. Much of that forest was ponderosa. The result has scientists and forest managers looking intensely at the area to try to understand what happens next.

Ponderosa is only one of the types of forest ecosystem found in the mountains of New Mexico. PiƱon-juniper of the lower elevations and the mixed conifer forest found in the Sangre de Cristos above Santa Fe burn differently, resulting in different patterns of revegetation. Damage from fires has been far less severe in those forest types. But ponderosa is a special case because of the special ferocity with which it has burned in recent years.

Also sometimes called “Western yellow pine,” the ponderosa is characterized by the cracked look of its orange bark and long needles.

Natural ponderosa forests once burned regularly, with low-intensity fires that cleared out undergrowth. But a century of fire suppression, along with logging practices that removed the largest, most fire-resistant trees, left the forests thick and flammable. Now when fires finally do arrive they often destroy entire stands of trees, something rare prior to the 20th century. The Jemez, partly because it has been particularly well studied by scientists over the years, has become Exhibit One in efforts to understand what happens next.

“That east flank of the Jemez has just been repeatedly hammered,” said University of Arizona forest scientist Tom Swetnam, who grew up in the Jemez and fought fires as a young man. “It’s going to be the poster child in the Southwest.”

What is most likely to happen next on those severely burned ponderosa landscapes, Swetnam said, is what ecologists call “type conversion” – the complete replacement of ponderosa-style forests by something different.

What shape that ecosystem might take is hard to say, according to Melissa Savage, a forester and professor emeritus at the University of California Los Angeles who has done some of the most detailed studies of what happens to ponderosa forests after large stand-replacing fires.

In some cases, according to a study of 10 burned Arizona and New Mexico sites done by Savage and colleague Joy Mast of Carthage College in Wisconsin, ponderosa returned – thick and unhealthy forest at risk of future fires. Some of those forests have already burned again since Savage and Mast studied them a decade ago.

Often, ponderosa did not come back, replaced by shrubs like the Gambel oak and New Mexico locust that have spread across the Jemez Mountains in the wake of previous fires, supplanting the ponderosa.

That is what happened on the mesa along the Dome Road after the Dome Fire in the spring 1996.

It was a forest that had been heavily logged in the past, Allen explained, and had returned as overgrown ponderosa, the sort of forest at high risk of wildfire.

Replanting is possible, according to Jon Williams, ecosystem staff officer for the Santa Fe National Forest. Forest staff is in the midst of evaluating the conditions in the burn area and formulating a plan for what happens next. But Williams acknowledged that, absent an existing ponderosa forest to serve as a nursery for new trees, it is hard to get the big pine trees started in drought-challenged New Mexico.

Savage’s reviews of past forest restoration efforts offer little encouragement to those who hope for human intervention to restore ponderosa forests in the Jemez, partly because of the difficulties of getting new plants to survive and partly because of the sheer scale of the burned areas.

“You can’t really plant much of the landscape,” she said.

Climate change further confounds efforts to predict what happens next in the Jemez Mountain ecosystem and other burned ponderosa forests. Temperatures now are consistently warmer than in the period during which the mountain ecosystems developed, and there is evidence that those conditions are putting the ponderosa under stress, even without fire. “Climate change is actually happening,” Savage said.

Standing on a high spot overlooking the worst of the Las Conchas burn, Allen tried to imagine the future of the mountain range he has lived and worked in for much of the past three decades.

“This isn’t going to be forest,” he said.