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U of O: Logging left legacy of erosion in Siskiyous


Erosion – much of it the legacy of decades-old logging practices – is a bigger threat to the Siskiyou forest than fire, new research shows.

Erosion – much of it the legacy of decades-old logging practices – is a bigger threat to the Siskiyou forest than fire, new research shows.

Clear-cut logging and related road-building in the 1950s and 1960s in southern Oregon’s Siskiyou Mountains disrupted soil stability and led to unprecedented soil erosion, University of Oregon researchers report.

Daniel G. Gavin, professor of geography, and postdoctoral doctoral researcher Daniele Colombaroli have analyzed charcoal, pollen and sediment taken from 30-foot-deep cores drilled below Upper Squaw Lake in the Rogue River-Siskiyou National Forest.

“There is a legacy of poor logging practices conducted decades ago,” Gavin said. “Road building during that period was done with little concern for subsequent erosion. The soils were much more heavily impacted by that development compared to the prehistoric fires of the past. Our study shows that at least four times more erosion occurred on the landscape after the logging and floods of the 1960s compared to the most severe prehistoric fire. So we are dealing with a more delicate, less-resistant ecosystem in the majority of areas that has seen this logging.”

Logging practices have improved dramatically over the past half-century, they say. But the damaged landscape — the removal of low vegetation that helps to protect hillsides during fires and rain — continues to pose a threat into the foreseeable future.

Their findings, which provide a look at the impacts of fires over the last 2,000 years, appeared online in an early edition of the Proceedings of the National Academy of Sciences.

The authors noted the findings suggest that managers could return public forests to their natural resiliency to help reduce damage from fire and erosion. However, Gavin said, the findings should be considered place-specific.

“They don’t apply widely throughout Oregon’s forests,” he noted. “The site is on the Oregon-California border, and is representative of what’s called mixed conifer — pines mixed with trees with shorter needles, especially Douglas-fir. This mix is common in southwest Oregon and northwest California, from I-5 west to near the coast.

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