OSU study: Logging, road building impacts landslides more than rain

CORVALLIS Ore. (KPTV) - A study released Wednesday by the Oregon State University College of Forestry indicates that landslides in the Pacific Northwest are more impacted by logging and road building than by heavy rain.

The research was led by forest engineering associate professor Catalina Segura and graduate student Arianna Goodman and was published in the journal “Earth Surface Processes and Landforms,” OSU said in a release.

Focusing on the Lookout Creek watershed in western Oregon, the team examined how often landslides happened and how severe they were compared to how much water was flowing through the area.

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The 64-square-kilometer Lookout Creek watershed is part of the H.J. Andrews Experimental Forest, a long-term research site in the Cascade Range funded by the National Science Foundation and the Forest Service. Logging and road building began in the Lookout Creek area in 1950 and mostly ended by the 1980s, which allowed scientists to track how forest management practices impacted landslides and floods.

“Understanding the long-term effects of forest practices like logging and road building is critical to sustainable forest management,” Segura said.

Researchers studied five time periods: 1950 to November 1964 (initial logging and road building; December 1964 to January 1965 (first major flood); February 1965 to 1995 (between-floods period); 1996 (second major flood); and 1997 to 2020 (post-flood period).

“In each of the five time periods, the frequency of landslides and debris flows depended on the conditions created by management practices during prior time periods,” Segura said.

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Segura said that during the first 15 years of road building and logging, landslides happened after even small floods.

“Big flooding in 1964-65, when harvesting was taking place, produced much larger geomorphic responses than the large flood of 1996, more than a decade after logging stopped,” Segura said.

But landslides were small or rare in 2011 during and after the third largest flood on record, the researchers found.

“By that time clear-cut areas of the forest had been replanted and the new trees were 20 to 70 years old,” OSU said.

People can follow this link for more information about the study.