During head fires, energy is vented above ground level (Trollope et al. 2002), with increases in wind speed producing faster moving fire fronts, decreasing the time of direct fire exposure to detritus and fallen woody material that may require prolonged exposure to fire before combustion is initiated (Rein 2013). Wind speed was highest during Fire A, alluding to a faster-moving fire front with lower assumed detritus ignition rates than Fires B and C, which had much lower wind speeds and higher mortality densities. Wind speed during fires thus seems to have an inverse proportional relationship to reptile mortality density, although more quantified replicates would need to be conducted to confirm this.
The spatial orientation within the environment during burning events may predispose or protect reptiles from fire effects. Species-specific habitat utilization may change due to torpor, seasonal migration, mating activity, body size, or maturity. Studies documenting the impact of fire on soil vertebrates are scarce (Bigalke and Willan 1982; Neary et al. 1999). Smith et al. (2012) recorded mortalities of leaf-litter reptiles following a wildfire, but none for true burrowing species. Burrowing is considered to offer protection to vertebrates from fire-related hazards (Russell et al. 1999; Engstrom 2010). Burrowing vertebrates are thought to be able to avoid fire-related hazards by digging deeper into the substrate (e.g., Neary et al. 1999). Our results from Tembe Elephant Park, however, indicated that burrowing reptiles were not necessarily protected from fire effects.
Strictly fossorial and fossorial reptiles were well represented within the Tembe Elephant Park samples (Table 1). The shallow burrowing behavior of the eastern sand skink (Branch 1998), seeking shelter from fire instead of fleeing, may result in increased fire mortality, as was recorded during Fire C (25 mortalities ha−1). The depth within the soil column at which fossorial reptiles occur may vary according to seasonal reproductive behavior (e.g., Haacke and Bruton 1978; Branch 1998). This may influence the susceptibility of burrowing reptiles to burning as some taxa may prefer shallow soil depths or the surface when seeking mating partners, potentially increasing the exposure of sexually mature adult animals to the effects of fire. Such mating-driven seasonal habitat selection may have resulted in the presence or absence or fluctuating rates of specific soil-adapted species in the observed mortality sample. Alternatively, seasonal use of the surface environment for feeding (e.g., Haacke and Bruton 1978) may predispose certain species to succumb to the effects of fire at specific times of year. Beaupre and Douglas (2012) considered snakes more vulnerable to fires during ecdysis as old, detaching skin impairs their ability to detect and avoid fires. The only snake specimen collected in the process of shedding was the southern African python from Fire B.
Among vertebrates, mortalities caused by fire have been studied extensively in humans, finding mortalities most commonly attributed to toxic gases as part of smoke inhalation. Peracute gas intoxication with carbon monoxide and hydrogen cyanide has been identified as the main mechanisms of death. Heat-induced cardiac arrest through vagal inhibition when hot air or steam is inhaled has also been implicated as an important cause of death during fires (Busuttil 2008; Gill and Martin 2015). The unburned condition of most specimens encountered during surveys prompted suspicion of particulate smoke inhalation as a possible cause of death for Fire C samples; however, the relative absence of carbon-rich particulate matter and the occasional presence of pulmonary oedema during histopathological examination suggested asphyxiation, heat-induced cardiac arrest, or gas intoxication, such as carbon monoxide and hydrogen cyanide poisoning, as the most likely mechanisms resulting in death. Only two eastern sand skinks were considered to have possibly succumbed to particulate smoke inhalation, as carbon particles were present in their airways.
The association of most collected specimens with microhabitats rich in leaf litter follow the fine-scale habitat selection described by Measey (2006) as well as Maritz and Alexander (2008). When considering the histopathological manifestation of detrital combustion on species sheltering in substrate, especially in Fire C, the advective transportation of heated gas products into underlying soil layers as described in Massman et al. (2010) may explain the prevalence of fire-associated mortality to strictly fossorial and fossorial reptiles. It is worth noting that the study site falls within an area that is considered rich in soil-living herpetofauna (Maritz and Alexander 2008) and the implications for these groups of animals may not be relevant for most of southern Africa.
The results from our surveys in Tembe Elephant Park describe potential mechanisms of fire-caused mortality and indicate reciprocity between fire season, environmental conditions, and life history traits in the absence of non-combustible refugia (e.g., rocks). Published observations of fire-induced reptile mortality within multiple types of fire-prone habitats will contribute to improved understanding and therefore predictive power to inform management decisions.
