Chapter 26

Landscape fragmentation can be a major threat to the persistence of species with very specific habitat and area requirements (e.g., Wilcove et al., 1986). Such a species is the northern spotted owl (Strix occidentalis caurina), whose populations are experiencing fragmentation at a number of spatial scales. The analyses we discuss here focus on the geographic scale (Lord and Norton. 1990) and are concerned with the fragmented pattern of oldgrowth forests that results from timber harvest. In the case of the northern spotted owl, concerns over the fragmentation of habitat have been translated into a specific plan for the owl's conservation (Thomas et al., 1990). In this chapter we report some of the models that were used to guide decisions and thinking about the size and geometry of the habitat reserves that form the core of this conservation plan. We would like to emphasize that we are reporting only a small fraction of the studies and analyses that have been pursued to help maintain spotted owl populations. and that our results represent the synthesis of a massive team effort. Before discussing the specific details of the models. we briefly discuss the general issues surround-