Durboraw, T. D., C. W. Boal, M. S. Fleck, and N. S. Gill. 2022. A century of varying-severity fire and forest structure recovery in Mexican spotted owl nesting habitat. Fire Ecology 18, 31 (2022). https://doi.org/10.1186/s42408-022-00158-z
Abstract Dry mixed-conifer forests of the southwestern United States are being rapidly reshaped by anthropogenically-driven fire regime change. Prior to EuroAmerican settlement, these forests experienced frequent surface fires but are now vulnerable to uncharacteristically large, high severity fires. Fire directly influences the structure and composition of these forested systems and, in turn, the wildlife that inhabit them. Thus, the changing fire regime results in uncertain consequences for vegetation dynamics and wildlife habitat. A southwestern mixed-conifer forest inhabitant of particular note is the Mexican spotted owl (Strix occidentalis lucida), which is federally listed as threatened. High-severity fire has been cited as the owl’s primary threat, but uncertainties surround the impacts of high severity fire on the threatened subspecies, particularly across a timeframe longer than a few years. Our objective was to explore the long-term (i.e., 100-year timeframe) effects of fire severity on elements of forest structure vital for Mexican spotted owl nesting. To accomplish this, we quantified desirable structural attributes for nest/roost habitat across burned (varying severity levels) and unburned (control) mixed-conifer forests within the last century. High severity fire has the strongest deleterious impact on elements of forest structure vital to Mexican spotted owl nesting, and although the structural differences between severity classes diminish with time, it took ≥80-100 years to reach the structural conditions desired for Mexican spotted owl nesting after stand-replacing fires. The most important attribute measured, canopy cover, required 90-100 years after high severity fires to reach levels known to support Mexican spotted owls. As fires increase in frequency, severity, and size compared to the last century, forests of the Sacramento Mountains will face an overall decrease in the structural conditions needed for Mexican spotted owl nesting habitat. Uncharacteristic high severity fire in particular poses an imminent threat to nesting habitat far into the future.