Increasingly frequent “megafires” in North America's dry forests have prompted proposals to restore historical fire regimes and ecosystem resilience. Restoration efforts that reduce tree densities (eg via logging) could have collateral impacts on declining old‐forest species, but whether these risks outweigh the potential effects of large, severe fires remains uncertain. We demonstrate the effects of a 2014 California megafire on an iconic old‐forest species, the spotted owl (Strix occidentalis). The probability of owl site extirpation was seven times higher after the fire (0.88) than before the fire (0.12) at severely burned sites, contributing to the greatest annual population decline observed during our 23‐year study. The fire also rendered large areas of forest unsuitable for owl foraging one year post‐fire. Our study suggests that megafires pose a threat to old‐forest species, and we conclude that restoring historical fire regimes could benefit both old‐forest species and the dry forest ecosystems they inhabit in this era of climate change.

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.

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Fuels‐reduction treatments are commonly implemented in the western U.S. to reduce the risk of high‐severity fire, but they may have negative short‐term impacts on species associated with older forests. Therefore, we modeled the effects of a completed fuels‐reduction project on fire behavior and California Spotted Owl (Strix occidentalis occidentalis) habitat and demography in the Sierra Nevada to assess the potential short‐ and long‐term trade‐offs. We combined field‐collected vegetation data and LiDAR data to develop detailed maps of forest structure needed to parameterize our fire and forest‐growth models. We simulated wildfires under extreme weather conditions (both with and without fuels treatments), then simulated forest growth 30 years into the future under four combinations of treatment and fire: treated with fire, untreated with fire, treated without fire, and untreated without fire. We compared spotted owl habitat and population parameters under the four scenarios using a habitat suitability index developed from canopy cover and large‐tree measurements at nest sites and from previously derived statistical relationships between forest structure and fitness (λ) and equilibrium occupancy at the territory scale. Treatments had a positive effect on owl nesting habitat and demographic rates up to 30 years after simulated fire, but they had a persistently negative effect throughout the 30‐year period in the absence of fire. We conclude that fuels‐reduction treatments in the Sierra Nevada may provide long‐term benefits to spotted owls if fire occurs under extreme weather conditions, but can have long‐term negative effects on owls if fire does not occur. However, we only simulated one fire under the treated and untreated scenarios and therefore had no measures of variation and uncertainty. In addition, the net benefits of fuels treatments on spotted owl habitat and demography depends on the future probability that fire will occur under similar weather and ignition conditions, and such probabilities remain difficult to quantify. Therefore, we recommend a landscape approach that restricts timber harvest within territory core areas of use (~125 ha in size) that contain critical owl nesting and roosting habitat and locates fuels treatments in the surrounding areas to reduce the potential for high‐severity fire in territory core areas.

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