Severe Wildfire Affects the Thermal and Moisture Regimes of At-Risk Turtle Nesting Habitat

Natural wildfire regimes are important for ecosystem succession, but increased frequency and severity of wildfire due to climate change can negatively alter habitat characteristics. In 2018, over 11,000 ha of a granite rock barrens landscape that extends along the eastern shoreline of Georgian Bay, Lake Huron, burned in a wildfire. This landscape is a biodiversity hotspot providing habitat for many species at risk, including Emydoidea blandingii (Blanding's Turtle) and Clemmys guttata (Spotted Turtle), where turtles nest in shallow soil deposits in cracks and crevices in the bedrock. The burned, open rock-barren habitat had 70% fewer available nesting sites, but suitability of remaining nest habitat was unknown. To assess the impact of the wildfire on the suitability of turtle nesting habitat, we compared soil properties and in situ thermal and moisture regimes at turtle-selected nest sites, burned and unburned rock barren habitat, and burned forested uplands that may provide newly available habitat as a result of increased canopy openness following fire. Burned and unburned rock barren habitats drained quickly following rainfall, similar to turtle-selected sites, whereas burned forested uplands drained more slowly and provided wetter incubation conditions. Burned forested uplands provided a comparable thermal regime to turtle-selected nest sites and were often moss-dominated, with a relatively open canopy. Hatch success was estimated to be 20% lower at burned rock-barren habitats compared to unburned sites. Our findings suggest that severe wildfire affects soil thermal and moisture regimes, which can negatively alter the suitability of nest habitat, but burned upland forests are likely to provide suitable nesting habitat for at-risk turtles in the first years following fire.