Effects of forest management on California Spotted Owls: implications for reducing wildfire risk in fire‐prone forests

Abstract

Management of many North American forests is challenged by the need to balance the potentially competing objectives of reducing risks posed by high‐severity wildfires and protecting threatened species. In the Sierra Nevada, California, concern about high‐severity fires has increased in recent decades but uncertainty exists over the effects of fuel‐reduction treatments on species associated with older forests, such as the California Spotted Owl (Strix occidentalis occidentalis). Here, we assessed the effects of forest conditions, fuel reductions, and wildfire on a declining population of Spotted Owls in the central Sierra Nevada using 20 years of demographic data collected at 74 Spotted Owl territories. Adult survival and territory colonization probabilities were relatively high, while territory extinction probability was relatively low, especially in territories that had relatively large amounts of high canopy cover (≥70%) forest. Reproduction was negatively associated with the area of medium‐intensity timber harvests characteristic of proposed fuel treatments. Our results also suggested that the amount of edge between older forests and shrub/sapling vegetation and increased habitat heterogeneity may positively influence demographic rates of Spotted Owls. Finally, high‐severity fire negatively influenced the probability of territory colonization. Despite correlations between owl demographic rates and several habitat variables, life stage simulation (sensitivity) analyses indicated that the amount of forest with high canopy cover was the primary driver of population growth and equilibrium occupancy at the scale of individual territories. Greater than 90% of medium‐intensity harvests converted high‐canopy‐cover forests into lower‐canopy‐cover vegetation classes, suggesting that landscape‐scale fuel treatments in such stands could have short‐term negative impacts on populations of California Spotted Owls. Moreover, high‐canopy‐cover forests declined by an average of 7.4% across territories during our study, suggesting that habitat loss could have contributed to declines in abundance and territory occupancy. We recommend that managers consider the existing amount and spatial distribution of high‐canopy forest before implementing fuel treatments within an owl territory, and that treatments be accompanied by a rigorous monitoring program.

Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California

“…In areas of California where woodrats are important prey, NSO and CASPO foraging habitat is characterized as a heterogeneous mosaic of physiognomic types and successional stages interspersed with mature, closed-canopy forest (Zabel et al, 1992(Zabel et al, , 2003Franklin et al, 2000;Tempel et al, 2014). Prey diversity and abundance is associated with heterogeneity in foraging areas (Roberts et al, 2011(Roberts et al, , 2015, while nesting stands are dominated by large, mature trees in a closed-canopy condition (Phillips et al, 2010).…”

“…Finally, Lehmkuhl et al (2013) suggested that management to restore resilience to disturbance in closed-canopy MSForests would likely increase forage for ungulates compared to a landscape impacted by fire exclusion and past grazing practices. Clearly, managers will need a way to evaluate how current MSForest landscapes have departed from historical successional pattern conditions to inform management of needed habitat diversity (Franklin et al, 2000;Gaines et al, 2010b;Tempel et al, 2014).…”

Effects of post-fire logging on California spotted owl occupancy

“…However, these sites were heavily post-fire logged on both private timberlands and National Forest lands (Bond and Hanson 2014: Appendix C), a fact that was not reported by Tempel et al (2014).…”

“…In fact these sites (PLA007, PLA065, PLA015, PLA109, PLA012, ELD060, PLA049 and PLA043) had not been occupied prior to the fire (based on spotted owl surveys conducted for the Forest Service, which were obtained from the agency). Many spotted owl sites have lost occupancy in recent years in this area likely due to extensive logging (Tempel et al 2014). Thus, the conclusion by Jones et al (2016), that the King fire caused the loss of occupancy in these sites, is not sound.…”

“…Thus, the foraging behaviour results of Bond et al (2009) and Jones et al (2016) can be reconciled, given the owls' tendency to avoid clearcut areas (Call et al 1992, Comfort et al 2016, while selecting intact, unlogged high-severity fire areas dominated by an abundance of snags (standing dead trees) and shrubs (Bond et al 2009). Tempel et al (2014) also reported an adverse effect of high-severity fires on California spotted owl site occupancy, mostly due to four sites that generally became unoccupied, or infrequently occupied, following the Star fire of 2001 on the Eldorado and Tahoe National Forests, amongst a sample size of 12 sites inside wildland fire areas.…”