Summit County Citizens Voice

A classic ponderosa pine forest landscape. PHOTO COURTESY USFS.

New study shows historic fire conditions much more variable than previously thought

By Bob Berwyn

SUMMIT COUNTY — Many recent forest management efforts along Colorado’s Front Range ponderosa pine belt have been aimed at creating widely spaced stands of trees, based on the conventional wisdom that those forests were historically shaped by low-intensity ground fires.

But severe, high-intensity fires were probably much more common in the region than previously believed, said Mark Williams, one of the University of Wyoming researchers who found that at least 80 percent of the ponderosa pine forests in the region were subject to moderate-to-intense fires that destroyed stands and created a patchwork structure, leaving some dense stands and some open forests.

The study, conducted by William Baker and Mark Williams, used extensive land survey data as well as physical evidence of fires, and covered about 4.1 million acres on the Mogollon Plateau and Black Mesa in northern Arizona, in the Blue Mountains in northeastern Oregon, and in the Colorado Front Range.

Some previous studies may have been hampered by the limitations inherent in tree-ring reconstructions from small, isolated field plots that may be unrepresentative of larger landscapes.

“The land surveys provide us with an unprecedented spatially extensive and detailed view of these dry-forest landscapes before widespread alteration” said Dr. William Baker, a co-author of the study and a professor in the Program in Ecology at the University of Wyoming. “And, what we see from this is that these forests were highly variable, with dense areas, open areas, recently burned areas, young forests, and areas of old-growth forests, often in a complex mosaic.”

The study also does not support the idea that frequent low-intensity fires historically prevented high-intensity fires in dry forests.

“Moderate- and high-severity fires were much more common in ponderosa pine and other dry forests than previously believed ” said Mark Williams, senior author of the study and recent PhD graduate of the University of Wyoming’s Program in Ecology. “While higher-severity fires have been documented in at least parts of the Front Range of Colorado, they were not believed to play a major role in the historical dynamics of southwestern dry forests,” he said.

The prevailing view of historic ponderosa pine fire ecology along the Front Range was probably the result of researchers extrapolating findings from ponderosa pine forests of the Southwest, in Arizona, for example, where there is more evidence for those historic conditions.

“The Southwest model has been adopted where it’s not appropriate,” Williams said.

But the new research does have implications for the Southwest, where recent major fires were commonly characterized as unnatural or catastrophic fires. Williams and Baker said those fires likely were similar to fires that occurred historically in these dry forests.

Williams said it’s important to remember that ponderosa pines are among the most widely distributed tree species in North America, ranging from Mexico to Canada. Given the wide variety of habitat, it’s to be expected that there would be regional variation in the ecology of the forest type, based on climate and other factors.

The fine scale of the new study enabled the researchers to show that, along the Front Range, there were even variations within the ponderosa pine belt, with low intensity fires and open forests more common at lower elevations. At the upper elevations, there were more signs that intense fires historically shaped large parts of the forest landscape.

The research suggests that current efforts to uniformly thin Front Range ponderosa forests and reduce fire intensity may be misguided and may not restore them. Instead, the aggressive management could take even farther from the natural historic range of variability with potential negative consequences for wildlife.

Special-concern species whose habitat includes dense forest patches, such as spotted owls, or whose habitat includes recently burned forests, such as black-backed woodpeckers, are likely to be adversely affected by current fuel-reduction programs.

Key findings:

•  Only 23-40 percent of the study areas fit the common idea that dry forests were open, park-like and composed of large trees.

•  Frequent low-intensity fires did not prevent high-intensity fires, as 38-97 percent of the study landscapes had evidence of intense fires that killed trees over large areas of dry forests.

•  The rate of higher-severity fires in dry forests over the past few decades is lower than that which occurred historically, regardless of fire suppression impacts.

The study was published online last week in the international scientific journal, Global Ecology and Biogeography. The published article can be accessed online here.

Filed under: Forest health, Environment, US Forest Service, forests, forest fires, Summit County news, climate and weather, Colorado Tagged: | fire ecology, fire history, forest thinning, Front Range, Ponderosa pines