Water and elevation are more important than burn severity in predicting bat activity at multiple scales in a post-wildfire landscape

Abstract

Bats are among the most widespread mammals on Earth, and are subject to habitat change, loss, and other disturbances such as fire. Wildfire causes rapid changes in vegetation that affect habitat use. However, the spatial scale at which these changes affect bats depends on their use of habitat elements. Three years post wildfire, we assessed how burn severity, water, landform type, elevation, vegetation type, and roads affected use by bats of a forest landscape at multiple spatial scales. We deployed acoustic detectors at randomly selected locations within a 217,712 ha wildfire boundary in Arizona. We classified echolocation calls to species or group and calculated an activity index by adjusting the calls per hour. We conducted a multi-scale analysis of landscape structure and composition around each location from a 90 to 5760 m radius. No scale was selected preferentially by any species or group. Stream density and elevation range were more important predictors for species groups than burn severity. When burn severity was a predictor, agile species had higher activity in areas that were unburned or had low severity burn. A heterogeneous landscape composed of high, medium, and low burn severity patches within a forest altered by large wildfires provided habitat for different bat species, but water density and range in elevation were more important for predicting bat habitat use than fire severity in this arid landscape. More than one spatial scale, representing local to landscape levels, should be considered in managing habitat for bats. In arid areas, such as the western United States, maintaining reliable water sources is important for bats. Managing these factors at multiple spatial scales will benefit bat species with different wing morphologies, echolocation call types, and habitat selections.

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

“…Our result that pyrodiversity was positively associated with bat richness across landscape scales supports findings that bat richness increases with pyrodiversity at finer scales (500 m) (Steel et al 2019), likely due to variable responses to burned area characteristics by bat species (Starbuck et al 2020) with different ecological and morphological traits (Blakey et al 2019). Interestingly, pyrodiversity was not correlated with vegetation structural diversity, which was unrelated to bat richness.…”

“…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).…”

“…Grey dashed lines show |R| = 0.7, an indicator of when variable collinearity may distort model estimation (Dormann et al 2013) Several limitations are important to consider when interpreting our results that may also be productive areas for future study. First, the burned areas assessed in our study represented a variety of different fires which burned since 1987 and encompassed a range of severities, which could partially explain the lower than expected correlations between burned and forested configurations and could influence relationships between bat richness and landscape variables given both burn severity and time since fire have been shown to influence bat occurrence (Blakey et al 2019;Steel et al 2019;Starbuck et al 2020). To partially assess the importance of this variability in fire regime, during the exploratory stage we ran models using only high severity burned areas to calculate the landscape extent and configuration variables and recorded similar modelled relationships.…”

“…Bats respond to habitat features at different spatial scales (Perry et al 2008;Mendes et al 2017;Starbuck et al 2020). At a fine scale (\ 100 m), habitat use is often driven by prey abundance or fine-scale habitat structure such as presence of water or edges (Morris et al 2010;Müller et al 2012;Blakey et al 2017a).…”

“…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.…”