Post-fire vegetation and bird habitat use in piñon-juniper woodlands

2022 Spring.Includes bibliographical references.Global climate change has caused fire activity and behavior to shift from historical norms due to hotter and drier conditions. Although the ecological effects of changing fire regimes have been explored in many systems, the resilience of some forest types, such as piñon-juniper, are often overlooked. Piñon-juniper is a dominant forest type in the western US and provides breeding habitat for many obligate or semi-obligate bird species. Similarly, this system is supported by a critical mutualism, where the regeneration and infilling of these trees is reliant on several bird species that disperse piñon pine and juniper seeds. This study aimed to assess woodland resilience by evaluating post-fire forest structure and the associated avian communities one-year and 20+ years post-fire. More specifically, seedling regeneration and the habitat use of piñon-juniper obligate bird species, semi-obligates, piñon seed dispersers, and juniper seed dispersers were compared across burned, refugia, and unburned patches. Replicate patches of each habitat type were selected within three fire locations, and 3-4 bird point count stations and 1 forest inventory plot were established in each patch. No tree regeneration was observed 1-year post-fire, and after 25 years, there were few juniper seedlings and no piñon seedlings observed in burned plots. Seedling regeneration and forest structure in refugia and unburned plots were not different, regardless of fire age. Results from occupancy models indicated that Woodhouse's Scrub-jay, a piñon seed disperser, used all habitats equally. American Robin had the highest habitat use in the recent burned patches. Obligate and semi-obligate bird species had differing responses to habitat types, with the habitat use of Ash-throated Flycatcher and Spotted Towhee not differing across habitat types, Virginia's Warbler having the highest habitat use in old burn and refugia patches, the Gray Vireo, Black-throated Gray Warbler, and Gray Flycatcher having highest habitat use in unburned, refugia, and recent burn patches, and the Blue-grey Gnatcatcher having the highest habitat use in the old burn. While there is a need for longer term studies, our work highlights that even 25 years post-fire, little tree recovery is observed and the associated bird species continue to differ, emphasizing the potential transition or long recovery time in these sensitive areas