Fire Management Effects on Long‐Term Gopher Tortoise Population Dynamics

Abstract

Long-term datasets are required to understand the response of long-lived organisms (e.g., gopher tortoises [Gopherus polyphemus]) to management actions, such as prescribed burns. Our objective was to estimate the effects of prescribed burning on gopher tortoise population dynamics over decadal time frames at Fort Stewart Army Reserve, southeastern Georgia, USA. We captured and marked adult tortoises from 1994-2020. In addition, since the early 1990s, managers at Fort Stewart collected spatial records of prescribed burns; thus, we could compare demography of the population to prescribed burning. We used a Bayesian hierarchical model (open population Jolly-Seber model) to estimate population parameters (emigration and survival, immigration and recruitment, and adult abundance) and their relationships with years since burn. We observed opposing responses to years since burn at 2 sites: abundance and the probability of staying (survival plus not emigrating) increased within 1 site when it had been more recently burned (F zones), but abundance and probability of staying in a second site increased when it had been longer since the site was burned (E zones). Some of these effects were weak but indicative of different responses to burning between the sites. Although the sites experienced similar burning regimes, they differed substantially in other habitat features: the F zones had almost twice the tree cover and lower soil sand composition, indicating that tortoise population responses to burning depend on habitat context. We inferred that the primary mechanism for demographic responses to years since burn was likely emigrating adults, which indicates the need for more detailed movement data. Our results demonstrate that gopher tortoise population responses to prescribed burning are complex, context dependent, and primarily influenced by tortoise movements. Therefore, prescribed burn plans may best accommodate spatially dynamic tortoise populations when they create spatial heterogeneity in burn ages within the range of typical tortoise movements.

Warming conditions boost reproductive output for a northern gopher tortoise population

“…Given that higher temperatures in these periods led to greater reproductive output, the warming trend in temperatures likely led to an increase in gopher tortoise reproductive output at FSAR. The change in temperature is a more likely driver of the increased reproductive output than an improvement in habitat, as FSAR has been consistently managed with prescribed burning for the last several decades (Hunter & Rostal 2021). Over the 25 yr study period, mean clutch sizes of reproducing females have increased by approximately 1 egg, a 15% increase based on the mean clutch size of 6.5 eggs.…”

“…Although adult tortoises are unlikely to be directly influenced by changes in climate, their habitats may be. Gopher tortoise habitats are managed with prescribed burning, and burning at FSAR has complex effects on adult population dynamics (Hunter & Rostal 2021). If burning becomes less frequent as temperatures warm, as is predicted (Kupfer et al 2020), there may be consequences for adult activity rates, foraging opportunities, and overall condition (Howell et al 2020), which could impact investment in reproduction.…”

Terrestrial laser scan metrics predict surface vegetation biomass and consumption in a frequently burned southeastern U.S. ecosystem

“…The understory is a diverse mixture of graminoids, forbs, and shrubs such as wiregrass ( Aristada stricta ), gallberry ( Ilex glabra ), and saw palmetto ( Serenoa repens ). Beyond military missions, the land is managed for a variety of plant and animal species, including the endangered Red-cockaded Woodpecker ( Picoides borealis ), regular timber harvesting and year-around prescribed burning on a 3–5 year interval is used to maintain desired canopy composition and density, as well as reduce fuels loads [52-54]. Our study site at Fort Stewart consisted of two adjacent burn units – F6.3 (261 ha) and F6.4 (397 ha) that was represented by longleaf pine flatwoods and intermixed cypress wetlands ( Taxodium spp.).…”

Terrestrial Laser Scan Metrics Predict Surface Vegetation Biomass and Consumption in a Frequently Burned Southeastern U.S. Ecosystem

“…The understory is a diverse mixture of graminoids, forbs, and shrubs such as wiregrass (Aristada stricta), gallberry (Ilex glabra), and saw palmetto (Serenoa repens). Beyond military missions, the land is managed for a variety of plant and animal species, including the endangered Red-cockaded Woodpecker (Picoides borealis); regular timber harvesting and year-round prescribed burning on a 3-5 year interval is used to maintain the desired canopy composition and density, as well as to reduce fuels loads [53][54][55]. Our study site at Fort Stewart consisted of two adjacent burn units, F6.3 (261 ha) and F6.4 (397 ha), which were represented by longleaf pine flatwoods and intermixed cypress wetlands (Taxodium spp.).…”