Forest Image

Type N Study Area

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Figure 1.  Location of study regions relative to major features of Washington state. 

Type N study sites are located in the Olympic Mountains, Willapa Hills, and Southern Cascades physiographic provinces in stream basins with competent basalt lithologies (Figure 1). Study site selection was limited to the geographic range of and to streams supporting the amphibian species targeted in this study—the tailed frog (Ascaphus truei), giant salamander (Dicamptodon spp.), and torrent salamander (Rhyacotriton spp.). Study basins are distributed on federal, state, and private forestlands managed for timber production

Study Design

The Cooperative Monitoring, Evaluation, and Research Committee (CMER), under appointment by the Washington State Forest Practices Board, commissioned an experimental study analyzing the effectiveness of buffer prescriptions on Type N stream basins.

Buffer Treatments

After selection, the study sites were grouped into five blocks of four stream basins each based on common attributes, such as stream length and aspect (Hayes et al. 2005). The stream basins in each block were assigned four buffer treatments using a randomized block design, with each buffer treatment replicated in each block.

The Type N study plan proposes four buffer treatments (Figure 2):

  1. A reference basin that will not be harvested.
  2. A clearcut basin with a 50 foot buffer on both sides of the stream along 100% of the perennial stream length, with the exception of yarding corridors as prescribed in the current rules
  3. A clearcut basin with the current Forests and Fish prescription of a 50-foot buffer along 50% of the perennial stream length, including buffers prescribed for sensitive areas
  4. A clearcut basin with no riparian buffer, but with a 30-foot equipment limitation zone along the entire perennial stream length (Hayes et al. 2005).

Figure 2.  Experimental buffer treatments applied to the Type N stream basins in each block.  Areas shaded in green represent an unharvested basin or buffer.  Areas without shading indicate a clearcut harvest.  Prescriptions for yarding corridors and equipment limitation zones, although not shown, apply to all harvested basins.  Figure adapted from Hayes et al. (2005).