Age‐dependent habitat relationships of a burned forest specialist emphasise the role of pyrodiversity in fire management

Abstract

Variation in fire characteristics, termed pyrodiversity, plays an important role in structuring post‐fire communities, but little is known about the importance of pyrodiversity for individual species. The availability of diverse post‐fire habitats may be key for fire‐associated species if they require different resources at different life‐history stages. We tested for age‐specific habitat relationships in the black‐backed woodpecker, a post‐fire specialist. We used radio‐telemetry to track fledgling and adult woodpeckers in burned forests and built resource selection functions to compare the effect of stand‐, tree‐ and snag‐level covariates between adults and fledglings. Fledgling black‐backed woodpeckers selected habitat with more live trees than adults and used more heterogeneous habitats burned at lower severity, illustrating strong age‐dependent effects on habitat selection. Within selected stands, fledglings were less likely to use snags and more likely to use live trees when compared to adults, but both age classes showed strong positive selection for larger‐diameter trees (live and dead). Over the 60 days after leaving their nests, fledglings showed an increasing propensity to use snags rather than live trees. Our results provide evidence that the predation–starvation hypothesis, which posits a trade‐off between foraging efficiency and the need to minimise predation risk, plays a role in structuring the age‐dependent habitat use of a burned forest specialist. Adult black‐backed woodpeckers selected resources associated with food availability, but these resources occurred in relatively open, exposed habitat. Fledglings selected habitat that provided increased cover, perhaps as a strategy to reduce predation risk. Synthesis and applications. Globally, fires are increasing in severity and extent, leading to increased focus on fire‐associated species that play keystone roles in facilitating biodiversity resilience. Our findings suggest that a diversity of patches burned at different severities may benefit post‐fire specialists like the black‐backed woodpecker at multiple life‐history stages. The increasing prevalence of large, homogeneously high‐severity ‘megafires’ may present an emerging threat even to post‐fire specialists, and we urge land managers to consider opportunities to promote pyrodiversity in the face of novel fire regimes.

When bigger isn’t better – implications of large high-severity wildfire patches for avian diversity and community composition

“…Additionally, edges of high-severity patches appear to accommodate individual bird species of conservation concern with otherwise contrasting habitat needs. While we found little effect of distance to patch edge on occupancy of breeding Black-backed Woodpeckers, other studies have found juveniles of the snag specialist preferred patch edges to interiors (Stillman et al 2019) and nest site suitability was lower toward the center of large patches (Campos et al 2020). On the other hand, the mature forest specialist Spotted Owl (Strix occidentalis) selects small high-severity patches (i.e., < 115 ha) and uses patch edges but avoids large patches and interior areas beyond approximately 100 m (Kramer et al 2020, Jones et al 2020.…”

Patterns of woodboring beetle activity following fires and bark beetle outbreaks in montane forests of California, USA

“…Response variables are defined in Table 4 and predictor variables are defined in Table 5 more common in particular quadrats where bark beetles were absent, suggesting that the local retention of woodborers might be enhanced by prioritizing retention of trees less heavily infested by bark beetles. Our observations that woodborer larvae were more abundant in smaller pine snags with more southerly exposure, that Xylotrechus Chevrolat 1860 adults were more common where the dominant host tree taxon was true fir, and that Monochamus species were more common where burn severity was low to moderate, can further inform design of snag retention patches that might effectively promote successional processes and provide prey for wildlife species like the black-backed woodpecker (Siegel et al 2018;Tarbill et al 2018;Stillman et al 2019).…”

Few detections of Black-backed Woodpeckers (Picoides arcticus) in extreme wildfires in the Sierra Nevada

“…We included covariates in our model that were uncorrelated and identified as important to Black-backed Woodpeckers in California including forest structure, elevation, and fire severity (Saracco et al 2011, Fogg et al 2014, Tingley et al 2015. Distance to unburned forest may influence nest predation (Saab et al 2011) and provide alternative habitat (Tingley et al 2014, Stillman et al 2019), therefore we also included the distance of the survey point to the outer fire perimeter, and the distance from the survey point to the nearest green patch (≥ 4 ha of forest that was classified as unchanged or burned at low vegetation severity). These two distance variables allowed us to make inferences about the impacts of the size of high-severity patches and heterogeneity in fire effects on detections of Black-backed Woodpeckers.…”

“…In a comprehensive study by Tingley et al (2018), they concluded that although fire size does not affect colonization rates, larger fires do have lower woodpecker densities. Lower densities of Black-backed Woodpeckers in contemporary fires may in part be explained by age-structured habitat requirements (Stillman et al 2019) that necessitate a mosaic of burn conditions. Alternatively, the later timing of the Rim and King fire may have indirectly affected Black-backed Woodpecker densities by limiting the colonization of their prey (Ray et al 2019).…”

“…Although the resulting fires may provide an abundance of dead trees indicative of Black-backed Woodpecker habitat, the scale and homogeneity of fire effects may alter habitat quality in unpredictable ways. For instance, distance to unburned forest may be much higher in these fires, which may be important to Blackbacked Woodpecker fledglings that select habitat with higher proportion of live trees than adult birds (Stillman et al 2019).…”