Effects of disturbance and management of forest health on fish and fish habitat in Eastern Oregon and Washington
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Effects of fire, forest insects and diseases, grazing, and forest health treatments on fish populations and habitat in eastern Oregon and Washington, USA are reviewed. Fire, insects, and disease affect fish habitat by their influence on the rate and volume of woody debris recruitment to streams, canopy cover and water temperature, stream flow, channel erosion, sedimentation, nutrients, and residual vegetation. Physical effects from fire vary greatly depending on fire severity and extent, geology, soil, topography, and orientation of the site, and subsequent precipitation. Most effects moderate within a decade. Post-fire erosion and wood recruitment are also influenced by fire lines, road construction, and timber harvest. Although some disturbances, such as severe fire and subsequent floods, appear catastrophic, and effects may last decades or centuries, natural disturbances help create and maintain diverse, productive aquatic habitats. Recolonization of fish populations following wildfires can be rapid and is related to occurrence of local refugia, life history patterns, access for migratory forms, and distribution of the species. In most livestock studies, grazing negatively affected fish habitat and populations, but results may vary depending on sites and specific grazing management. Effective approaches to grazing management similarly depend on the specific application and the commitment of operators and managers. Restoration of the structure, function, and processes of watersheds more similar to those with which native species evolved may favour those species; however, there is little documentation of the aquatic effects of those activities. Risk from vegetative treatments may be minimized by experimenting outside of critical areas (i.e., conserving key habitats and populations, focusing intensive treatments on upland sites). Use of more benign techniques (e.g., lower-impact logging systems) and pulsed treatments consistent with characteristics of natural disturbance regimes are other considerations for achieving both terrestrial and aquatic objectives.