Initial impacts of wildfire on overwintering conditions for a Species-at-Risk snake

Peatlands are important ecosystems that are becoming increasingly vulnerable to climate-mediated disturbances such as wildfire, which can threaten peatland hydrological, biogeochemical, and ecological function. However, the magnitude of these changes and their impacts to peatland-dependent species worldwide is a key knowledge gap. Peatlands in the eastern Georgian Bay, Ontario, region provide overwintering habitat for the eastern massasauga rattlesnake (Sistrurus c. catenatus), a species considered at-risk across its North American range. Overwintering habitat is considered suitable when peat temperature is above 0°C and the water table position provides moisture without risk of prolonged flooding. This combination of suitable ecohydrological conditions, also known as the life zone or resilience zone, commonly occurs in hummocks which are raised microforms on the peatland surface. Due to a changing climate, peatlands are at risk of increased wildfire frequency and burn severity which may reduce overwintering habitat availability and suitability through changes in peat thermal and hydrological properties. In 2018, a wildfire burned over 11,000 ha of the eastern Georgian Bay landscape which supports critical habitat for the massasauga at the northern limit of the species range. To assess the potential impact of wildfire on massasauga overwintering habitat, we monitored water table position, snow depth, and peat thermal dynamics in hummocks across a burn severity gradient (unburned to severely burned) in three burned and three unburned peatlands across three winters (2019–2022). We found that hummocks were able to provide unflooded habitat above 0°C regardless of peat burn severity; however, there was moderate evidence that hummock burn severity influenced mean daily resilience zone size. Overall, hummock overwintering suitability appears to be dominantly controlled by peatland surface topography and interannual winter weather. With the frequency and intensity of wildfires predicted to increase globally under a changing climate, it is critical to understand how interannual variability of winter weather conditions influences overwintering habitat suitability after wildfire, to identify peatland ecosystems that provide resilient species at risk habitat.