Forest stand structure of the northern spotted owl's foraging habitat.

Abstract

Although the spotted owl's close association with old growth has been extensively studied, it more difficult to identify and quantify the abundance of particular stand structures associated with preferred owl foraging sites. Old-growth forests have a suite of characteristics that distinguish them from younger forests but which also make it difficult to isolate individual structural features important to the spotted owl. This study used an analysis of use-only sites in areas where natural disturbance had created a gradient of old-growth structural characteristics. We used radio telemetry data collected from reproducing owl pairs to locate sample stands and compute a relative measure of owl-use intensity in each stand. Snag volume and tree height class diversity (a measure of canopy layering) were the stand structures significantly associated with owl foraging intensity. Stands with 142 m3/ha of intact snags and a high diversity of tree heights had medium or high foraging use by spotted owls. In these old-growth stands, biological legacies (e.g., large trees and snags) produced by past disturbance provide important associated with spotted owl foraging use.

Citation

North, Malcolm P.; Franklin, Jerry F.; Carey, Andrew B.; Forsman, Eric D.; Hamer, Tom. 1999. Forest stand structure of the northern spotted owl''s foraging habitat. Forest Science. 45(4): 520-527.