Impacts of Low, Moderate, and High Severity Fire on Herpetofauna and their Habitat in a Southern USA Mixed Pine/Hardwood Forest
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The primary goals of this dissertation were: 1) to increase our knowledge of fire impacts on amphibians and reptiles, collectively referred to as herpetofauna, the least studied major terrestrial vertebrate groups in relation to fire research; 2) to improve our understanding of fire severity as a factor influencing the response of ecosystem components to fire; and 3) to increase our understanding of the temporal and spatial ecology, and impacts of fire, on the invasive red imported fire ant (RIFA; Solenopsis invicta), a species which has been implicated in the decline of several herpetofaunal species, and for which almost no information exists concerning fire impacts. I accomplished this through the completion of 6 field-based studies in the Lost Pines ecoregion of Texas. I used low and moderate severity prescribed fire to manipulate the habitat, and incorporated unplanned high severity wildfires into my study designs.
The herpetofaunal investigations indicated that direct mortality from fire was not significant, even for high severity wildfires. Further, survivorship of juvenile amphibians may have increased following a moderate severity summer prescribed fire, and the potential increase in survivorship could have been related to a reduction in arthropod predation. The high severity wildfire research indicated the post-wildfire landscape provided suitable habitat for herpetofauna ca. 6 months after the wildfire, which is directly opposed to the general assumption of wildlife managers in the area that the fire killed the majority of herpetofauna and destroyed their habitat. In addition, movement-rates of Hurter’s spadefoot toads (Scaphiopus hurterii) appeared to increase following the wildfire, and to my knowledge this was the first study that investigated the impacts of fire on amphibian movement-rates.
The study investigating the influence of fire severity on responses of ecosystem components to fire indicated that fire severity was an important factor, and the influence was related to magnitude, but not direction, of effects. For some components (e.g., pond nutrient levels) the magnitude effect was clear, whereas for others (e.g., species composition of understory vegetation) it was dichotomous in that no effect was apparent for low severity fire and a strong effect was apparent for high severity fire. An additional important finding was mortality of loblolly pine (Pinus taeda) trees was nearly 100% in the high severity wildfire zone, and subsequently loblolly pine tree recruitment was low. Thus, restoration of the Lost Pines will require significant active management through reseeding of loblolly pines, with the alternative being a shift to hardwood-dominated forest patches in the high severity wildfire zone.
The RIFA investigations indicated that peak annual RIFA activity coincides with the period when juvenile Houston toads are found at high densities around breeding ponds, and thus are particularly vulnerable to population-level impacts of predation. Further, there was a strong inverse relationship between RIFA captures and overstory canopy cover, and high severity fire appeared to positively affect RIFA through reduction in canopy cover. This is a concerning result given the substantial tree mortality across the high severity wildfire zone, and thus the potential for increases in RIFA abundance and distribution in the Lost Pines ecoregion.