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Study: Wider Streamside Forest Buffers Aid Fish


Buffers of trees near streams are now left on forest lands in Oregon to provide cooling shade and woody debris that protect fisheries.

Buffers of trees near streams are now left on forest lands in Oregon to provide cooling shade and woody debris that protect fisheries.

Oregon State University/Flickr

No-logging zones along state forest streams are making a difference in keeping temperatures cool for fish, according to a study issued Wednesday by Oregon State University.

The study compared water temperatures in streams in Oregon state forests with those of rivers and creeks that flow through private forestlands. After nearly a decade’s worth of logging, it found no increase in the average temperature on state forests, but a 1.3 degree increase on private timber lands.

Jeremy Groom, the report’s author, said limitations on streamside logging — which differ for state forests and private timber lands — are a factor in the study’s water-temperature findings.

Oregon’s Forest Practices Act sets streamside buffer requirements for logging on state and private forest. The private forest tracts in the study follow the minimum requirements, while the state forests’ managers have opted for more stringent protections than required by law.

Private timber lands: No-cut buffers 20 feet from streams. Limited harvests up to 70 feet from streams.

State forests: No-cut buffers 25 feet from streams. Limited harvests up to 170 feet from streams.

Groom said the broader stands of trees along streams keep temperatures cool in large part by casting shade on the water for longer periods of time, compared with the shade cast where forests have been logged closer to streamsides.

The research was done over the past nine years on 33 sites in the Oregon Coast Range by scientists from the Oregon Department of Forestry and Oregon State University. It made no conclusions about whether the 1.3 degree temperature increase on private forest lands is a concern for fish health. The study was only designed to examine regulatory stream temperature compliance.

Stream temperatures are a particular concern for cold-water fish such as trout and salmon, and the Oregon Department of Environment Quality mandates that forest management activities should not increase temperatures by more than 0.5 degrees Fahrenheit, according to an OSU release on the new study.

This was one of the larger studies of its type ever done, examining multiple sites for two years before harvest and five years afterward. All of the streams studied were fish-bearing, and the primary objective was to evaluate the effectiveness of forest practice rules in protecting stream temperatures and promoting riparian structure.

Although only the Coast Range was studied, the findings are probably applicable to many other regions with similar physical and biological characteristics, the researchers said, including other areas of the Pacific Northwest, California, Alaska and British Columbia.

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