Assessing the response of California spotted owls to forest fuels and vegetation treatments

Background/Question/Methods

Forests in western North America have changed in structure and function over the past 150 years a result of fire suppression, which has altered the primary natural disturbance agent in these ecosystems, and other management activities such as timber harvest and grazing. Current management strategies proposed to restore and conserve these ecosystems are often politically controversial as a result of uncertainty regarding the effects of proposed treatments on species of concern and ecosystem processes. Uncertainty surrounding the effects of fuels and vegetation management on California spotted owl (CSO) population viability has been at the heart of the controversy to develop ecologically sound and socially acceptable forest management strategies in the Sierra Nevada, California.  The objective of our work is to assess the effects of fuels and vegetation management on CSOs across a 1900 km² study area in the northern Sierra Nevada.  We annually monitor the distribution, abundance, occupancy, and demographics of CSOs across the study landscape. We use these baseline data to model habitat suitability and project how habitat and CSO numbers may change under alternative management strategies. Direct field monitoring is then continued during and following project implementation to assess both short- and long-term responses of CSOs.   

Results/Conclusions

Approximately 75-90 territorial CSO sites have been annually monitored between 2003-2008. To date, implementation of fuels and vegetation treatments have been largely stalled because of political and legal challenges and controversies. The first suite of landscape-scale fuels and vegetation treatments were completed in 2007-2008 on a 240 km² project area. We documented similar numbers of CSO territorial sites across the project area in the first year following treatments, although two individual site territories may have shifted spatially in association with treatments within core areas. Additionally, in 2008 we monitored CSO distribution and abundance across an 88,000 acre area that burned under high severity wildfire on the edge of our study area. We documented a single territorial pair of CSOs within the burned area. Our results are providing information on CSO habitat associations across a range of untreated, treated, and wildfire-burned landscapes that can be used to address uncertainties surrounding risk associated with fuels and vegetation treatments versus wildfire risk. Our design illustrates the importance of considering effects at both the home range-individual CSO pair and landscape-population spatial scales for species such as CSOs when assessing the effects of fuels management and vegetation restoration in forest ecosystems.