Impact of fire frequency on choosing the optimal site for coastal cactus wren habitat restoration

Background/Question/Methods . Habitat fragmentation and increased fire frequency are common threats to wildlife in Mediterranean ecosystems.  Whereas the remaining Southern California coastal sage scrub serves as refuge for rare flora and fauna, this habitat is threatened by frequent, human-ignited wildfires.  The coastal cactus wren, a California Bird of Special Concern, serves as a “canary in the coal mine” for a variety of coastal sage species (e.g., the California gnatcatcher and orange-throated whiptail) because the wren depends on mature stands of coastal sage scrub (and the presence of fire-sensitive Opuntia and Cylindropuntia species).  In collaboration with park managers and conservation groups, we model the optimal sites for cactus restoration within San Diego County, using a population model created from maps of wren abundance, cactus habitat, land use, and predicted fire probability.  Wildfire risk is estimated by relating previous fire locations to a variety of demographic and environmental variables.  The model is constrained by an overall limit on the amount of additional habitat created.  We compare models that treat fire frequency in a spatially explicit manner, to models that consider only an average fire frequency over the region.  

Results/Conclusions . The optimal management strategy – augmenting existing habitat patches or creating new “stepping stone” patches to connect existing patches – in addition to the optimal site for habitat restoration depends on how fire frequency is modeled.  When fire frequency is considered in a spatially explicit manner certain sites emerge as optimal for restoration that are not identified when average fire frequency is considered.  Results also depend on (i) wren dispersal distance, (ii) post-fire habitat recovery, and (iii) the magnitude of edge effects on the smallest patches.