Changing Snow Conditions and Shifts in American marten (Martes americana) distribution in Michigan's Upper Peninsula

Abstract

Climate change is forcing many species to shift their ranges northward and to higher altitudes. Information on the extent of these shifts and the mechanisms driving them are urgently needed to inform conservation planning. Here, we explore the impact of changing climatic conditions on American marten (Martes americana) occupancy in Michigan’s Upper Peninsula, part of the greater Northwoods, where they are of high economic, cultural, and ecological importance. Using marten harvest data reported to the Michigan Department of Natural Resources between 2005 and 2020 we employ ensemble species distribution models aggregated into 5-year periods to investigate if the occurrence and projected distribution of American marten has shifted over time in Michigan’s Upper Peninsula in response to changing climatic conditions. Our results show a gradual decrease over time in marten occupancy in the southern Upper Peninsula facilitated by a decrease in suitable abiotic conditions over the last two decades. Average winter temperature was the most important variable across models, with average winter snow depth increasing in occupancy effect-size over the study period. Areas containing suitable snow depth and winter temperature conditions in the Upper Peninsula have decreased by nearly 10% over the study period coupled with an overall decrease in overall occupancy probability across the region. These observed changes in marten occupancy and abiotic conditions will likely impact ecosystem processes and services in the Northwoods moving forward. Future research will focus on identifying regions in the Upper Peninsula that will continue to have suitable climatic conditions for martens under varying climate projections.