Fuels Reduction in a Western Coniferous Forest: Effects on Quantity and Quality of Forage for Elk

Abstract

Use of mechanical thinning and prescribed fire to reduce fuels in dry forest ecosystems has become increasingly common in western North America. Nevertheless, few studies have quantified effects of fuels reduction treatments on wildlife. We evaluated effects of fuels reduction on quantity and quality of forage available to elk (Cervus elaphus) in northeastern Oregon. From 2001 to 2003, 26 stands of true fir (Abies spp.) and Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) were thinned and burned, whereas 27 similar stands were left untreated to serve as experimental controls. We estimated percentage of cover, percentage of in vitro dry-matter digestibility (digestibility), and percentage of nitrogen (%N) of 16 important forage species and genera in treatment and control stands during spring (May-June) and summer (July-August) of 2005 and 2006. Quantity and quality of forage were lower in summer than spring in both stand types. In contrast, total cover of forage was higher in treatment than in control stands during spring, whereas the opposite was true during summer. For graminoids, %N was higher in control than in treatment stands whereas digestibility did not differ between stand types. For forbs, neither index of forage quality differed between stand types. When treatment stands were separated by years since burning, %N and digestibility of forbs and %N of graminoids increased from 2 to 5 yr following treatment, and by the fifth year after burning had exceeded maximum values observed in control stands in both seasons. As a result of the interacting effects of fuels reduction and season on forage characteristics, treated stands provided better foraging opportunities for elk during spring, whereas control stands provided better foraging opportunities during summer. Consequently, maintaining a mosaic of burned and unburned (late successional) habitat may be of greater benefit to elk than burning a large proportion of a landscape.