Populations are constantly changing spatially and temporally, even within a single ecosystem. They shift seasonally, annually, and in response to biotic and abiotic pressures. Investigation into factors that influence population dynamics across the landscape is therefore a constant focal point for ecological researchers, conservation biologists, and land managers. For example, disturbances can have impacts on populations at different spatial and temporal scales (Odum et al. 1979, Pickett and White 1985, Menges and Marks 2008, Quintana-Ascencio et al. 2018). Fire, a common global disturbance, may have an immediate impact via mortality or emigration, but also have longer lasting impacts due to habitat alteration, resource availability, and chemical leaching (Wilbur and Christensen 1983, Russel et al., 1999, Noss and Rothermel 2015, Jones et al., 2020).
Fires occur worldwide, and in some regions and ecosystems this natural disturbance is frequent enough that it becomes a major driver of the population dynamics for many species (Kauffman 2004, Noss 2013). Prescribed or controlled fires are increasingly utilized as a proxy for these more hazardous and unpredictable natural wildfires. In the United States (US), prescribed fire is one of the most common methods used by land managers to attempt to restore this critical ecological process while safely reducing fuel loads and burn intensity on natural lands (USDA and USDI 2002, Pilliod et al. 2003, Pausas and Keeley 2014).
The pine savannas of southeastern U.S are closely linked to fire. These ecosystems evolved with relatively short lightning-induced fire return intervals of about 2–5 years (Komarek 1968, Barnett 1999, Noss 2013). Many of the constituent species in these fire-prone ecosystems require frequent fire for reproduction, and most recover quickly from burns (FNAI 2010). While optimal fire intervals for ecosystem persistence are relatively well understood, the potential for fine-scale modifications to accommodate species responses to fire is an important consideration for scientists and land stewards (Noss 1987, 1996). Fine-scale adjustments within coarse-level conservation and management plans have been effectively implemented for many species, such as pre-burn understory thinning for cavity trees of red-cockaded woodpeckers Picoides borealis Vieillot (Williams et al. 2006), deliberate hardwood patch protection for Sherman’s fox squirrel Sciurus niger shermani (Perkins et al. 2008) and vehicle buffers to prevent burrow collapse for gopher tortoises Gopherus polyphemus Daudin (Smith et al. 2015).
Plants native to these systems have numerous strategies for persisting in pyrogenic ecosystems, including but not limited to seed banks, underground storage organs, fire-resistant bark, and resprouting (Outcalt 2000, Noss 2013, and those cited within). Consequently, and appropriately, fire management is mainly based on outcomes for plants (Driscoll et al. 2010). While plants are forced to endure a fire, animals have different options. When a fire occurs, or any other disturbance, animals face three main pathways which can be generalized to escaping, hiding in place, or dying (e.g., Peterman et al. 2011). While each of these mechanisms occurs simultaneously at the individual-level, each can have different population impacts. Populations that go through a mass mortality or significant exodus event may experience a temporary or permanent extirpation. When the prevailing mechanism is to hide in-place, however, we should expect a local population to be present immediately post-disturbance. Studies that focus on individual- and population-level mechanisms are therefore necessary to fully understand fire-influenced dynamics (Russel et al. 1999, Driscoll et al. 2010).
Given that fire is an essential process that maintains structural, compositional, and dynamic properties in these ecosystems, we need to understand how nontarget groups respond. Amphibians are typically not considered for fire management, yet they are good models for looking at prescribed fire impacts. Amphibians have limited mobility, are sensitive to chemical perturbations, require special microhabitats, and have been experiencing enigmatic declines around the globe (Blaustein et al. 1995, Stuart et al. 2004). An overwhelming majority of amphibian studies to date have focused on collecting data at breeding events in wetlands, which often represents only a snapshot of this group’s life histories (Boughton et al., 2000, Pilliod et al. 2003, Klaus and Noss 2016, Robertson et al. 2018). Treefrogs, in the family Hylidae, are particularly interesting because they require both upland and wetland ecosystems for their life cycle but spend most of their lives in those uplands and out of water. Furthermore, this group is unique among amphibians because they readily ascend into the canopy layer of trees. Studies and anecdotal observations note that at least some age classes of treefrogs in the southeast prefer to be above the ground (Wright and Wright 1949, Boughton et al. 2000, Windes 2010, I.N. Biazzo personal observations). To the best of our knowledge, no studies have looked at hylid occupancy above the 4m height in the US (i.e., above the shrub or undergrowth layer) and considered impacts of fire or other disturbances on these vertical dynamics.
We used a before-after-control-impact experimental design combined with mark-recapture to examine impacts of prescribed fire on apparent survival, movement, and abundance of treefrogs in pine flatwoods in central Florida, U.S. To observe treefrogs, which use natural cavities to avoid desiccation and predation, we set polyvinyl chloride (PVC) pipes in trees as artificial refugia which they could enter and exit at will (Buchanan 1988, Boughton et al., 2000, Schurbon and Fauth 2003, Zacharow et al. 2003, Glorioso and Waddle 2014). While the pine flatwoods are home to four native treefrog species in central Florida, 99% of individuals observed in our study were one specialist species, the pinewoods treefrog (Dryophytes (Hyla) femoralis Bosc, Fig. 1), (Klaus and Noss 2016). We focused on the following questions regarding this specialist species: 1) What are the base-level pre-fire abundance, apparent survival, and movement of frogs in trees? 2) Does fire change these parameters? 3) If so, then which is the prevailing mechanism of population change during a fire?