Prescribed fire leads a pine flatwoods specialist treefrog to seek local refugia

Abstract

Pine savannas of the southeastern United States evolved with frequent low-intensity wildfires. Today, land managers use prescribed fires to restore this ecological process while also controlling vegetative fuel accumulation. Given the ubiquitous application of this management tool, studies should consider impacts on target and nontarget taxa in these systems. During fires, animal populations persist in the landscape when individuals emigrate to unburned areas or seek refugia within the burn zone; otherwise, they experience local extirpation. We examined the effect of prescribed fires on a pine flatwoods specialist frog, the pinewoods treefrog Dryophytes femoralis, in a frequently burned pine landscape. Treefrogs, though usually not considered explicitly in burn plans, are a good model system because they are often abundant, have both upland and wetland needs, spend most of their lives out of water, have limited mobility, and have skin susceptible to desiccation. We compared variation in abundance and survival in a before-after-control-impact study with prescribed fire as the experimental treatment. We used 240 plastic pipe refugia to sample populations in 8 circular plots over 27 months and 7 independent prescribed fires (one fire spanned two plots). Plots received prescribed fire during the growing season (March–July) in 2020 (N = 3 plots) or 2021 (N = 5 plots). We removed pipes from the plot before the burn and from another plot not getting burned that day to control for pipe removal impacts, then returned all pipes immediately after the fire. We observed 1805 individuals with 1790 additional recaptures. We modeled population trends and survival using mark-recapture techniques and mixed linear models with a Bayesian framework. Apparent survival was commensurate across plots and prescribed fire treatments after controlling for the effects of the pipe removal, and population trends were similar overall. We observed seasonal variation in survival, with populations showing lower apparent survival during wet-season months. The limited impact of low-intensity prescribed fires on apparent survival suggests that pinewoods treefrogs persist in the landscape by seeking refugia. Future work and management should consider possible refugia for target and nontarget taxa while continuing to focus on the physiognomy of pine savannas in burn plans.