Factors determining the abundance and occurrence of Hermann’s tortoise Testudo hermanni in France and Spain: Fire regime and landscape changes as the main drivers

Abstract

Major landscape transformations have occurred in the northern Mediterranean over the last decades, including urbanization, agricultural intensification and land abandonment, which, in turn, increase the risk of the propagation of fire. We used repeated-count surveys conducted at 369 sites in France and Spain to jointly model the effects of environmental covariates on the abundance, occupancy and detection of Hermann’s tortoise, a long-lived and endangered species, using a novel zero-inflated approach. We also employed a large dataset of presence-only data collected in Provence to model environmental influences on occurrence probability using maximum entropy models. In both France and Spain, sites that experienced wildfires over the last 50years hosted 31% fewer individuals than unburned sites. In Provence, higher wildfire frequency decreased this species’ occurrence probability, from 50% when 0–1 fire had occurred over the last 50years, to 7% in areas that had burned at least 3 times. We also showed that abundance required a long recovery time (more than 25years) after wildfires. In Provence, the highest occurrence probability for this species was found in patchy landscapes and scrub and/or herbaceous vegetation. The lowest species occurrence was found in extensive artificial areas, vineyards and arable lands. These results suggest a high risk of population extinction in the future if these types of habitats continue to expand in plains and coastal areas to the detriment of scrublands. Higher wildfire frequency predicted by climate change scenarios in the Mediterranean is also likely to increase the risk of extinction for some populations.