Climate change is the primary driver of white-tailed deer (Odocoileus virginianus) range expansion at the northern extent of its range; land use is secondary.

Quantifying the relative influence of multiple mechanisms driving recent range expansion of non-native species is essential for predicting future changes and for informing adaptation and management plans to protect native species. White-tailed deer (Odocoileus virginianus) have been expanding their range into the North American boreal forest over the last half of the 20th century. This has already altered predator-prey dynamics in Alberta, Canada, where the distribution likely reaches the northern extent of its continuous range. Although current white-tailed deer distribution is explained by both climate and human land use, the influence each factor had on the observed range expansion would depend on the spatial and temporal pattern of these changes. Our objective was to quantify the relative importance of land use and climate change as drivers of white-tailed deer range expansion and to predict decadal changes in white-tailed deer distribution in northern Alberta for the first half of the 21st century. An existing species distribution model was used to predict past decadal distributions of white-tailed deer which were validated using independent data. The effects of climate and land use change were isolated by comparing predictions under theoretical "no-change between decades" scenarios, for each factor, to predictions under observed climate and land use change. Climate changes led to more than 88%, by area, of the increases in probability of white-tailed deer presence across all decades. The distribution is predicted to extend 100 km further north across the northeastern Alberta boreal forest as climate continues to change over the first half of the 21st century.