Taxonomic and functional response of a Mediterranean reptile assemblage to a repeated fire regime

Abstract

Wildfires are common disturbances that have a major impact on ecosystems. Recent decades have seen an increase in fire frequency and extension due to the combined effects of climate change and land-use history. We studied the taxonomic and functional response of a reptile assemblage to repeated fires in southern France to understand shifts in dominant species and diversity, as well as the mechanisms that underlie responses according to functional traits of species. In the spring of 2010, we sampled reptiles in areas with three types of fire regime: unburned, burned once (2003) and burned 4–5 times (last fire in 2003) along a fire history of 51-years period. With this field sampling design, we examined the intermediate disturbance hypothesis and the habitat accommodation model of succession as methods to predict reptile responses to natural fire regimes. We also compared habitat structure at the study area between 1944 and 2006 to certify that repeated-fire regimes have modified the habitat for reptiles. The comparison of the habitat structure between both periods demonstrated that repeated-fire regimes modified the landscape from a homogeneous sparse forest to a contrasted heterogeneous mixture of scrubland and dense forest. We found a loss of reptile diversity after one and multiple fires, a result that contradicts the intermediate disturbance hypothesis. Reptile composition differed among the three fire regimes: there was a shift in dominant species and a reduction of beta diversity related to an increase in the number of fires. We also observed a functional response to repeated fires, with an increased frequency of insectivorous reptiles, which live in open areas, are specialists in their ecological niche, and have a short lifespan. These results suggest that reptile replacement according to fire regime accounts for a habitat accommodation model following particular traits of species. Our study indicated that areas subjected to repeated fires have a more strictly Mediterranean reptile assemblage than unburned areas, due to the ability of Mediterranean species to survive thermal environments in open (burned) areas. At a regional scale, changes in dominant species between unburned and repeatedly burned areas might be an argument for maintaining a patchwork of areas burned at variable intervals. However, the increase in fire frequency and extension suggests a future scenario of extinction for species negatively impacted by fire, such as the endangered Hermann’s tortoise Testudo hermanni, for which the study area is home to one of the last native populations in the western Mediterranean.