UC Santa Barbara

The frequency of high-severity “mega-fires” has increased in recent decades, with numerous consequences for forest ecosystems. In particular, small mammal communities are not only vulnerable to post-fire shifts in resource availability, but also play a critical role in forest function. Inconsistencies in prior observations of small mammal community response to fire severity underscore the importance of examining mechanisms regulating fire severity effects on post-fire recovery. Here, we compare small mammal abundance, diversity, and community structure among habitats burned at varying fire severity, and use vegetation characteristics and small mammal functional traits to predict community response to fire severity. We captured 544 small mammals at 27 sites in three fire severity categories (unburned, low-moderate severity, and high severity) three years after a mega-fire in the California Sierra Nevada. We measured five vegetation variables known to predict small mammal communities, and determined three small mammal functional traits associated with resource use for the captured species. Using a model-based fourth-corner analysis, we examined how interactions between vegetation variables and small mammal traits regulated post-fire small mammal community structure among fire severity categories. We found that overall small mammal abundance remained similar after fire, although diversity decreased and community structure shifted. Differences between unburned and low/moderate-severity sites were generally minimal while differences between unburned and high-severity sites were large. Three highly correlated fire-dependent vegetation variables (density of live trees, percent litter cover, and percent shrub cover) as well as volume of soft coarse woody debris were most associated with small mammal community structure. Furthermore, we found that interactions between these vegetation variables and three small mammal resource-use traits (feeding guild, primary foraging mode, and primary nesting habit) successfully predicted community structure among fire severity categories. We conclude that resource use is likely important for regulating post-fire small mammal recovery, since vegetation provides necessary resources to small mammals as determined by their functional traits.- Given the mechanistic nature of our analyses, these results can be applied to other fire-prone forest systems. - We suggest using these results to inform management decisions about fire severity.