Characteristics of young forests used by spotted owls on the western Olympic Peninsula, Washington

Although the dependence of spotted owls (Strix occidentalis) on older forests has been well documented, the specific attributes of comparatively younger forests used by owls have not been described in some regions. We collected habitat data at locations used by spotted owls tracked in an intensive radio-telemetry study to develop descriptions of these forests on the western Olympic Peninsula, Washington. After addressing the effects of triangulation error on the placement of our vegetation sampling plots, we collected data at all 16 telemetry locations that could be clearly associated with non-old-growth habitat, as well as 16 random locations. Owl locations were divided into 2 groups to reflect single-use (only one radio location within the error polygon) and multiple-use sites (gtoreq2 radio locations within the error polygon) within home ranges. Vegetation data collected in three arrays of variably-sized plots included measures of stem and snag density (by diameter class), canopy cover, and cover of downed wood and shrubs. Our analyses indicated that single-visit and random locations did not differ with respect to the variables we recorded. However, both differed from multiple-use locations in abundance of larger snags, and amount of canopy closure. A logistic regression model indicated that multiple-use sites could be reliably distinguished from single-use and random locations based on the greater number of snags gtoreq51 cm diameter at breast height (dbh) and gtoreq70% canopy closure. Younger forests managed for spotted owl foraging habitat in this region should be in the understory reinitiation stage of stand development, have gtoreq70% canopy closure, and contain gtoreq4 snags/0.4-ha that are gtoreq51 cm dbh. The habitat definitions we propose may not be applicable to other areas characterized by different forest types and prey assemblagesBuchanan et al "Characteristics of young forests used by spotted owls on the western Olympic Peninsula, Washington." Northwest Science. 1999; 73(4): 255-26