Torching Invasive Trees Revives Rangeland Perennials

Western juniper trees have thrived in Oregon’s high desert for about 6,000 years, but in the past century, the aggressive conifer has begun to dominate some of the region’s sagebrush grasslands. In Burns, Oregon, Agricultural Research Service rangeland scientists Jon Bates and Tony Svejcar are finding ways to manage this arboreal invasion and prompt the recovery of perennial grasses and forbs.

Although rangeland managers use controlled burns to keep ahead of the juniper, they also just cut down the problem trees and leave them where they fall. This protects the soil, but the dead trees pose an increased fire risk—and may also create conditions that encourage establishment of cheatgrass, an invasive annual that fuels fierce wildfires.

Bates and Svejcar conducted a study at a site dominated by a 90-year-old western juniper woodland—a site once vegetated with basin big sagebrush and associated perennial grasses and forbs—to determine whether burning the cut junipers would help reestablish the perennials. Burning was done during two consecutive winters after cutting. A control group of felled trees at the site was left unburned.

Results indicate that burning the trees when soils were frozen prompted a more successful recovery of perennials and helped keep cheatgrass establishment at bay. Ten years after burning, total perennial grass cover was 1.5 to 2 times greater in the areas where trees had been burned than in the areas where they were not burned. Perennial grass density was 60 percent greater in the burned areas than in the unburned areas, and cheatgrass was twice as dense in the control area as in the two burned areas.

The scientists concluded that native perennial communities could recover from juniper invasions most effectively when the felled junipers were burned rather than cut and left. Burning in winter, when soils were wet or frozen, helped limit damage to existing perennials at the site and gave them a head start in their growth the following spring, when they needed an edge against invasive annuals.—By Ann Perry, Agricultural Research Service Information Staff.

Jon Bates and Tony Svejcar are with the USDA-ARS Range and Meadow Forage Management Research Unit, Eastern Oregon Agricultural Research Center, 67826-A, Hwy. 205, Burns, OR 67826; (541) 573-8932 [Bates], (541) 573-8901 [Svejcar].

"Torching Invasive Trees Revives Rangeland Perennials" was published in the August 2010 issue of Agricultural Research magazine.