The effects of wildfire severity and pyrodiversity on bat occupancy and diversity in fire-suppressed forests

Abstract

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.

Extent, configuration and diversity of burned and forested areas predict bat richness in a fire-maintained forest

“…Similarly, due to fire suppression and climate change, modern fire regimes are less variable than historically (Cansler and Mckenzie 2014;Safford and Stevens 2017), with an increase in larger and more homogenous high severity burned patches (Steel et al 2018). The positive relationships we found between bat richness, burned area extent, burned patch size and edge density, along with other studies showing high resilience of bat communities in Western forests to fire, also indicate that bats of the region may be adapted to shorter fire intervals (Buchalski et al 2013;Steel et al 2019;Starbuck et al 2020). We may expect the negative relationship we observed between bat richness and forest cover to become positive after a threshold of forest fragmentation due to fire or other mechanisms, given positive relationships that have been demonstrated between bats and vegetation cover in agricultural, urban (Threlfall et al 2011;Bailey et al 2019), and fragmented tropical landscapes (Rocha et al 2016).…”

“…Negative relationships between forest continuity and bat richness were consistent across scales, at odds with our predictions. This may be because the bat community of our study area is adapted to historically more heterogenous forests and relatively short-interval fire regimes (Steel et al 2019). Present-day forests of the Northern Sierra Nevada are likely to have greater forest continuity and extent of dense forest than they did historically (Lydersen and Collins 2018).…”

“…Insectivorous bats are highly mobile predators that respond to forest structure and fire based on their diverse call and morphological traits (Schnitzler et al 2003;Denzinger and Schnitzler 2013;Blakey et al 2019). At fine spatial scales (B 500 m), bats adapted to open areas and many edge-adapted species benefit from higher burn severity and more frequent fire (Armitage and Ober 2012;Buchalski et al 2013;Inkster-Draper et al 2013;Cox et al 2016;Blakey et al 2019;Steel et al 2019). Bats also use edges and openings created by timber harvest (Law et al 2016b and references therein).…”

“…The scale at which bats respond most strongly to habitat varies with their mobility, as well as morphological and call traits (Farneda et al 2015;Fuentes-Montemayor et al 2017), leading to scale-dependent relationships between landscape structure and bat richness (Mendes et al 2017). To date, landscape-scale effects of fire on bat communities have included investigation of the extent of high severity burned area at 2 km scale (Buchalski et al 2013), burn severity and pyrodiversity at scales B 500 m (Steel et al 2019) and burn severity at scales from 90 m to 5,760 m (Starbuck et al 2020). The landscape diversity and configuration of burned and forested areas have not been investigated simultaneously and the influence of the configuration of burned areas on bat communities remains unstudied.…”

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

“…Thus, our finding that edges of high severity patches support greater species richness is consistent with past research showing many western bird species are tolerant or even benefit from creation of habitat edges McComb 1995, Sisk andBattin 2002), and that variation in burn severity is positively associated with bird diversity (Tingley et al 2016). Diversity of other taxa in the Sierra Nevada including bats (Steel et al 2019) and plant-pollinator communities (Ponisio et al 2016) also increase with variation in burn severity suggesting that pyrodiversity likely promotes biodiversity generally. Although a landscape composed of a variety of patch sizes may promote biodiversity, many of the large patches assessed in this study far exceeded the estimated natural range of variation where the majority of high-severity patches were likely less than 10 ha (Safford and Stevens 2017).…”