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Why streams are warmer on private timberland

Oregon State University

How many trees should be left along streams after logging operations? A nine-year study of 33 sites in Oregon’s Coast Range found that the minimum buffer under the state forest practices law leaves streams warmer than they should be under state water quality rules.

A study by Oregon State University suggests that the Oregon forest practices law doesn’t require large enough stream buffers for private logging operations.

OSU researchers have found that logging leaves streams warmer on private timber lands than it does in Oregon’s state forests. And warmer than state water quality regulations allow.

Warmer water, of course, is not good for cold-water fish such as salmon and trout. That’s why state environmental regulations say logging shouldn’t raise stream temperatures more than .5 degrees Fahrenheit.

Over the course of nine years, OSU researchers studied 33 sites on the Coast Range and found that average stream temperatures were 1.3 degrees higher after private timber harvests that left the minimum size stream buffers. That’s better than the 3- to 21-degree increases the streams saw in the 1970s, but still out of compliance with the state’s mandate that forest management activities shouldn’t raise stream temperatures by more than .5 degrees. 

Timber harvests on state forest lands didn’t raise average water temperatures at all. That’s probably because the state requires larger buffers of uncut trees around streams and allows fewer clearcuts than the private sector.

The OSU researchers didn’t comment on whether the warmer streams are a problem for fish health. But the study does make an important point about the state’s minimum requirements for stream buffers. Oregon’s Forest Practices Act dictates the rules for logging private timberlands. Critics have long said it’s too lenient, and doesn’t do enough to protect streams and fish from private logging operations.

According to OSU, many private landowners leave more than the minimum buffer required by law, but the study only examined lands using the minimum requirements.

The study, one of the largest of its kind, aimed to evaluate whether state forest practice rules are actually protecting stream temperatures. Hm…looks like the answer is no?


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