Research Highlights Wildfire's Mixed Impacts

TUCSON, Arizona, August 5, 2002 (ENS) - Scientists are presenting a variety of research into the benefits and risks of wildfire at the annual meeting of the Ecological Society of America in Tucson this week. The studies show that fire is an integral part of a healthy forest - but it can also help forest enemies like invasive plants and insects.

This morning, researchers presented studies on the relationship between fire, fire suppression and the health of forest ecosystems across the United States. One study suggests that without fire, red pines could disappear from the nation's northern forests, such as Minnesota's Boundary Water Canoe Area.

Years of fire suppression can lead to a buildup of fuels like downed trees and brush, leading to devastating wildfires that consume mature trees. Here, elk seek refuge from a fire in Montana in August 2000. (Photo by John McColgan, courtesy the Alaskan Type I Incident Management Team, National Fire Information Center)

Fires destroy understory vegetation, allowing red pines to reproduce more easily. "The fires cleared dense brush so the red pines could drop their seeds on the forest floor and also triggered the release of seeds from pine cones belonging to other fire adaptive trees," Scheller explained.

When settlers started taking active measures to suppress natural fires, red pines experienced more difficulty regenerating: other trees and shrubs filled the forest understory.

"Red pines have a life span of about 300 years," said Scheller, "and many of the ones in BWCA are already old." Without fire to help them reproduce, he added, it is unlikely that the older trees will be replaced once they die.

The U.S. Forest Service is now considering the use of fire in the boundary waters area, a proposal that Scheller's study supports. His model shows that continued fire suppression would lead to the disappearance of not just red pines but also jack pine, aspen and birch trees within 300 years.

"If full fire suppression continues, the forest may never recover and red pine may be lost as a locally dominant species," Scheller concluded.

On Tuesday, the Ecological Society conference will look at interactions between invasive plants and wildfire in several studies carried out by researchers from the U.S. Geological Survey. Nonnative plants are often positioned to invade disturbed areas, including areas scorched by fire.

Invasive buffelgrass can fuel scorching desert fires, killing hundred year old saguaro cacti like these in Arizona's Saguaro National Park. (Photo by Todd Esque, courtesy USGS)

However, the regeneration of many native plant species depends on natural disturbances such as fire. Matt Brooks of the USGS will look at how land managers can learn which types of disturbances help native plants, and which help invasive species gain a foothold, in a presentation called "Fire and other forms of disturbance: are they similar and do they have similar effects on invasive plants."

Several species of invasive plants that have colonized the Mojave Desert can increase the frequency of wildfires, enable fires to spread over large areas, and increase the desert's susceptibility to future fires, says Dustin Haines of the USGS. In some areas, repeated burning has eliminated native perennial plants and converted desert scrub into annual exotic grasslands.

USGS scientists are developing models to predict how some Mojave Desert habitats may be affected in the future by increased fire, exotic plant invasions and climate change. Haines will detail this research in "Fire and exotics in the Mojave Desert: an irreversible change?"

Fires in the desert also may eliminate natural stores of seeds from native plants, argues USGS research Todd Esque in "Seed bank variation in Mojave desertscrub relative to wildfire, granivores and invasive species."

On Wednesday, USGS researcher Phillip van Mantgem will discuss how land managers can predict which trees will die following a fire, in order to assess how fire might affect natural landscapes. His research could help managers plan prescribed burns or restoration efforts after a wildfire.

On Thursday, Eric Knapp of the USGS will present complimentary research on the use of fire to thin accumulated fire fuels in the Sierra Nevada. Some researchers and land managers are concerned that the long fire free interval in these forests may result in intense fires that could kill old growth trees.

Forest thinning projects, aimed at reducing the risk of wildfire, can allow invasive species to gain a foothold in the forest. (Photo courtesy Martos Hoffman, Native Forest Network)

Prescribed fire killed only a small percentage of the largest trees, and removed many of the small trees that contribute to increased danger of severe wildfire. Knapp's presentation is titled "Tree mortality following reintroduction of fire to an old growth mixed conifer forest."

For more information on the Ecological Society of America's annual conference, visit: http://www.esa.org/Tucson