The Fire & the Tortoise

Fire maintained ecosystems are often found in geographic regions with Mediterranean climates - southern California, southwest Australia, and of course the Mediterranean. Burning vegetation is an inconvenience, and even prescribed burns are often objected to by local citizens. But, burning-off left-over agricultural biomass has increased in many places. Suppressing fires can lead to the build-up of fuel -dead, dry vegetation- in fire maintained ecosystems and result in increased hazards to both humans and wildlife. How wildlife populations deal with fire is of interest for understanding adaptations to fire and for conservation. Ana Sanz-Aguilar and colleagues have examined how the Iberian Spur-thighed Tortoise, Testudo gracea ibera, manges to coexist with fire at the Cumbres de la Galera Biological Reserve in the Sierra de la Carrasquilla, in Spain. Their study area supported a high density population (about 20 tortoises per hectare) of Spur-thighed Tortoise and they estimated tortoise populations in areas that had frequent fires and areas that had not been burned. The Spur-thighed Tortoise is a long-lived species of the Mediterranean shrublands and the tortoises spend much of their lives sheltered under the vegetation or underground in burrows. These tortoises also bury themselves for hibernate and aestivate, so that they are protected from extreme temperatures, predators and possibly from fires. They found fire caused direct and delayed reductions in local survival, with young individuals being the most affected. Fire-related mortality was highest in juveniles and subadults than adults; this seemed to be related to differences in burrowing behavior. Summer fires had a lesser impact on adults because they spend summer and winter underground in burrows or by burying themselves to avoid temperature extremes. Juveniles and subadults tend to use more superficial burrows or take cover under the vegetation only a few centimeters in depth, thus and are exposed to higher temperature and smoke. The study areas that had fire frequencies similar to those occurring in areas uncontrolled for burns (less than one fire every 20–30 years) tortoise populations were able buffer the effects of fires. But, when fire frequency increased the probability of extinction dramatically increased, except for the largest populations. Thus, T. graeca is able to cope with natural fire frequencies, but the effects of more recurrent fires may severely threaten the species.

Citation:Sanz-Aguilar, A., J. D. Anadon, A. Gimenez, R. Ballestar, E. Gracia, and D. Oro.. 2011. Coexisting with fire: The case of the terrestrial tortoise Testudo graeca in mediterranean shrublands. Biological Conservation (2011), doi:10.1016/j.biocon.2010.12.023

Fire & Tortoises

Humans have altered Mediterranean landscapes and ecosystems for more than 8000 years, and despite human influences the region is considered a biodiversity hotspots. In the last few decades fire suppression policies have modified the ecosystems’ functioning, but prescribed burning has been considered a management tool to prevent extensive wildfires and restore the dynamics of fire-maintained ecosystems. Anna Sanz-Aquilar and colleagues (2011) assessed the impact of fire on survival rates, reproduction and movement of the Mediterranean Spur High Tortoise, Testudo graeca ibera, at the Cumbres de la Galera Biological Reserve, in the Sierra de la Carrasquilla, Spain. They found fire impacted survival of mostly of young individuals, with dramatic mortality of juveniles with the burned areas during the first and the second year after the fire. The reduction in vegetation cover after a fire could increase the visibility of young and vulnerable individuals to predators interfere with thermoregulatory behavior, or effect food availability. They found no differences in fecundity and movement patterns of tortoises between burned and unburned areas. Their, population models showed areas with fire frequencies of less than one fire every 20–30 years the tortoise populations seemed to cope with the effects of fires with little damage to the populations. But, when this fire frequency was surpassed, the probability of population extinctions exploded for all populations, except for those with the largest numbers of individuals. Thus, tortoise populations may be able to deal with naturally occurring fire frequencies, but the effects of more frequent fires may severely threaten the species. 

Citation
Sanz-Aguilar, A., J. D. Anadón, A. Giménez, R. Ballestar, E. Graciá and D. Oro. 2011. Coexisting with fire: The case of the terrestrial tortoise Testudo graeca in mediterranean shrublands. Biological Conservation, In Press. doi:10.1016/j.biocon.2010.12.023