Study shows forest practices protect core salmon temperatures in forested streams


A recently released decade-long study looking at several aspects of water quality, including temperature and sediment, show that current forest practices rules as outlined in the Forests & Fish Law are protective of fish.

Beginning in 2007, the study measured temperature, sediment and other parameters of water quality two years before a harvest on forestland that is home to non-fish bearing waters that flow into fish bearing waters. Then, for nine years after harvest, the study continued to measure the same factors related to water quality. Temperatures, specifically, were measured at the height of summer in July and August.

The study found that while there was a small, temporary thermal pulse (averaging 1.8 degrees Centigrade) immediately after harvest, stream temperature never exceeded 14.1 degree C, well below the 16 degree C threshold established by the Washington Department of Ecology for the most common type of fish-use found on private forest lands. 


The study represented a more extreme case for harvest than is common. Landowners rarely harvest an entire basin leaving only the buffers – strips of trees and other vegetation left adjacent to the streambanks for the purpose of mitigating the impacts of the harvest nearby – required under current rules. But such a harvest could happen within current rules, and so the study was designed to test the impact of that possibility.

The study also focused on streams with bedrock stream beds, a type of lithology commonly referred to as “hardrock”.  A similar study focusing on “softrock” streambeds is expected to produce similar results.

The current forest practices rules are the result of the historic Forests and Fish Agreement that was adopted into law nearly 22 years ago by the legislature and signed into law by Gov Gary Locke.  Not only did the Forest and Fish Agreement create the most fish-protective rules on private forestlands in the nation, but the landmark law also established a highly effective Adaptive Management process for studying the effectiveness of rules and adjusting them if inadequacies were found.  So far, very few rule changes since the 1999 agreement have been necessary, demonstrating the effectiveness of the agreed rules.

The Hardrock study was an important undertaking, not solely for the purpose of assessing how forest practices support water quality on fish-bearing streams, but also because the science done under the state’s Adaptive Management Program reduces uncertainty and contributes to a process for change that is science-based and not driven by politics.  By ensuring that proposals are analyzed using a common, neutral set of scientific observations, Washington state ensures that the science is always in the lead.