One of the largest and longest studies done in Oregon on the impact of timber harvest on stream temperatures has found no average temperature increases on state forest lands, but a 1.3 degree increase on private timber lands.
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.
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.
Although only the Coast Range was studied, researchers say 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.
Since broad forest management regulations were first implemented in the 1970s and then expanded in later decades, any increases in stream temperatures are far less than they used to be. According to past research, historic forest management practices sometimes left no buffer zone at all around streams and allowed temperature increases from 3 degrees to 21 degrees.
“One thing that’s clear is that forest management practices are now much, much better,” said Jeremy Groom, lead author on the study and a research associate in the OSU Department of Forest Engineering, Resources and Management. “On average, Coast Range state forest lands are being fully protected from temperature changes.
“Earlier in the 1900s, it was common to clear cut and burn forests right down to the stream edge, sometimes even dragging logs through the stream with heavy equipment,” Groom said. “State and federal regulations are now far more stringent about stream protection.”
This research, Groom said, was done largely to determine whether or not those regulations are having their intended effect. The work was a collaboration of the Oregon Department of Forestry with university, private industry, state and federal agencies, the EPA and other groups.
The study examined only private and state-owned timber lands, not those managed by the National Forest Service or Bureau of Land Management. The private and state-owned lands actually operate under the same regulations, Groom said, but the state chooses to use larger buffers around streams and more partial timber harvests than are required by law. Many private landowners also leave more than required by law, but the study examined only those using minimum requirements.
There was considerable variability based on individual sites studied, but with current management approaches used by the state of Oregon, the streams had no change in temperature. The primary influence on stream temperature is shade provided by trees, the research made clear, although there are many other factors as well.
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.