RESERVE DESIGN FOR TERRITORIAL SPECIES - THE EFFECTS OF PATCH SIZE AND SPACING ON THE VIABILITY OF THE NORTHERN SPOTTED OWL

Designing a reserve system for a threatened territorial species such a s the Northern Spotted Owl requires the balancing of biological necess ity against economic reality. The Spotted Owl conservation plan and th e Pacific Northwest timber industry are in conflict because both deman d large areas of mature and old-growth coniferous forests. The primary focus of this paper is the efficient design of a reserve system for t erritorial species with obligate juvenile dispersal We examine the rel ationship between the degree of aggregation of suitable owl habitat, t he level of occupancy of that habitat by pairs of Spotted Owls, and th e likelihood of owl persistence given different amounts and spatial ar rangements of suitable habitat across the landscape We develop a popul ation model for Spotted Owls that includes an abstracted forest landsc ape where suitable owl habitat is arrayed in clusters embedded in a ma trix not suitable for owl habitation. We conclude from our study of th is model that, for any given fraction of the landscape set aside in re serves, the level of occupancy (efficiency of use) of that area will i ncrease as the aggregation of suitable habitat increases. After the re serves reach a size that includes territories for 20 to 25 owl pairs, however, there are diminishing returns from further increases. Preserv ing connectivity and increasing the geographical extent of the reserve begin to outweigh increased size in importance in insuring the long-t erm viability of the species.