Wildfire is an important ecological process that influences species’ occurrence and biodiversity generally. Its effect on bats is understudied, creating challenges for habitat management and species conservation as threats to the taxa worsen globally and within fire-prone ecosystems. We conducted acoustic surveys of wildfire areas during 2014–2017 in conifer forests of California’s Sierra Nevada Mountains. We tested effects of burn severity and its variation, or pyrodiversity, on occupancy and diversity for the 17-species bat community while accounting for imperfect detection. Occupancy rates increased with severity for at least 6 species and with pyrodiversity for at least 3. Two other species responded negatively to pyrodiversity. Individual species models predicted maximum occupancy rates across burn severity levels but only one species occurred most often in undisturbed areas. Species richness increased from approximately 8 species in unburned forests to 11 in pyrodiverse areas with moderate- to high-severity. Greater accessibility of foraging habitats, as well as increased habitat heterogeneity may explain positive responses to wildfire. Many bat species appear well adapted to wildfire, while a century of fire suppression and forest densification likely reduced habitat quality for the community generally. Relative to other taxa, bats may be somewhat resilient to increases in fire severity and size; trends which are expected to continue with accelerating climate change.

ABSTRACT. Black-backed Woodpeckers (Picoides arcticus) are a rare habitat specialist typically found in moderate and high severity burned forest throughout its range. It also inhabits green forest but little is known about occurrence and habitat use patterns outside of burned areas, especially in the Sierra Nevada of California, USA. We used point count and playback surveys to detect Black-backed Woodpeckers during 2011 -2013 on 460 transects on 10 national forest units. We defined green forest as areas that had not burned at moderate or high severity since 1991 and were more than 2 km from areas burned at moderate or high severity within the previous eight years (n = 386 transects). We used occupancy models to examine green forest habitat associations and found positive relationships with elevation, latitude, northern aspects, number of snags, tree diameter, lodgepole pine (Pinus contorta) forest, and a negative relationship with slope. Estimated occupancy in green forest was higher than previously understood (0.21). In addition site colonization and extinction probability in green forest were low (0.05 and 0.19, respectively) and suggest that many of the individuals detected in green forest were not just actively dispersing across the landscape in search of burned areas, but were occupying relatively stable home ranges. The association with high elevation and lodgepole pine forest may increase their exposure to climate change as these elevation forest types are predicted to decrease in extent over the next century. Although density is high in burned forest, green forest covers significantly more area in the Sierra Nevada and should be considered in efforts to conserve this rare species.Tendance dans l'occurrence du Pic à dos noir dans les forêts vertes de la Sierra Nevada, Californie, États-Unis RÉSUMÉ. Le Pic à dos noir (Picoides arcticus) est un spécialiste rare qui fréquente les forêts modérément à fortement brûlées dans l'ensemble de son aire de répartition. Il s'observe également dans les forêts vertes, mais les tendances dans l'occurrence et l'utilisation de l'habitat à l'extérieur des secteurs brûlés, tout particulièrement dans la Sierra Nevada, aux États-Unis, sont très peu connues. Nous avons effectué des dénombrements par points d'écoute et à l'aide d'enregistrements sonores pour détecter le Pic à dos noir le long de 460 transects situés dans 10 unités de forêts nationales, en 2011-2013. Selon notre définition, une forêt verte n'a pas brûlé de modérément à sévèrement depuis 1991 et est localisée à plus de 2 km de secteurs qui ont brûlé de modérément à sévèrement au cours des huit années précédentes (n = 386 transects). Nous avons utilisé des modèles de présence pour examiner les associations avec les forêts vertes et avons trouvé une relation positive avec l'altitude, la latitude, l'orientation vers le nord, le nombre de chicots, le diamètre des arbres et les forêts de Pin tordu (Pinus contorta), ainsi qu'une relation négative avec la pente. L'occurrence estimée dans les forêts vertes était plus élev...

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Abstract. Non-linear and interacting effects of fire severity and time since fire may help explain how pyrodiversity promotes biodiversity in fire-adapted systems. We built on previous research on avian responses to fire by investigating how complex effects of burn severity and time since fire influenced avian community composition across the northern Sierra Nevada, California. We conducted avian point counts from 2009 to 2015 in 10 fires that burned between 2000 and 2014, resulting in a chronosequence of 1-15 yr post-fire. We estimated the effects of burn severity, time since fire, non-linear and interacting effects of fire severity and time since fire, pre-fire forest conditions, and several physiographic parameters on the density of 44 breeding bird species using hierarchical distance sampling models. In addition, we fit separate models to observations of each species in unburned forest to compare species' densities between burned and unburned forests. At least one of the non-linear or interaction fire effects was significant for 27 (61%) of the 44 bird species. The quadratic effect of time since fire was an important predictor of post-fire densities of 20 species, illustrating the dynamic nature of this post-wildfire avian community. Greater maximum densities were estimated at some combination of burn severity and time since fire than in unburned forest for 13 of the 44 (30%) species, only one of which reached maximum density following low-severity fire. In contrast, all of the 12 species that were more abundant in unburned forest reached maximum post-fire densities in fires that burned at low severity. Results from the study suggest that consideration of the non-linear and interacting effects of fire severity and time since fire is important to fully understanding post-wildfire responses for a majority of birds. Moreover, the study supports a growing body of literature that indicates mixed-severity fire is essential for conserving avian diversity in many fire-maintained systems.