Influence of timber harvesting on headwater peak stream temperatures in a northern Idaho Watershed

Abstract

Concerns regarding the impacts of contemporary timber harvest practices on stream water temperature emphasize the need for improved understanding of temperature patterns and changes related to disturbances in headwater catchments. A network of water temperature recorders was installed in the Mica Creek Experimental Watershed in northern Idaho to investigate the relationships among forest treatments, stream temperatures, and riparian cover. Sensors were placed in first-order, nonfish-bearing unimpacted reaches, nonfish-bearing harvested reaches, and downstream into second- and third-order fish-bearing reaches of the stream network. Treated watersheds consisted of 50% canopy removal by contemporary clearcut methods and selective cut practices. Riparian canopy cover in the first-order reaches was measured during the pretreatment and posttreatment periods with a spherical densiometer. Despite estimated increases of up to 3.6°C in the directly impacted nonfish-bearing reaches, there was no significant increase in water temperature maxima at the downstream fish-bearing sites. Results also demonstrate that water temperatures in headwater stream networks can be highly variable and that the potential shade value of understory vegetation in harvested areas should not be overlooked. Continued monitoring at these sites is planned to evaluate peak water temperature trends during canopy regrowth and hydrologic recovery. Copyright © 2007 by the Society of American Foresters.