Climate change is likely to have major impacts on the distribution of planted and natural forests. Herein, we demonstrate how a process-based niche model (CLIMEX) can be extended to globally project the potential habitat suitable for Douglas-fir. Within this distribution, we use CLIMEX to predict abundance of the pathogen Phaeocryptopus gaeumannii and severity of its associated foliage disease, Swiss needle cast. The distribution and severity of the disease, which can strongly reduce growth rate of Douglas-fir, is closely correlated with seasonal temperatures and precipitation. This model is used to project how climate change during the 2080s may alter the area suitable for Douglas-fir plantations within New Zealand. The climate change scenarios used indicate that the land area suitable for Douglas-fir production in the North Island will be reduced markedly from near 100% under current climate to 36–64% of the total land area by 2080s. Within areas shown to be suitable for the host in the North Island, four of the six climate change scenarios predict substantial increases in disease severity that will make these regions at best marginal for Douglas-fir by the 2080s. In contrast, most regions in the South Island are projected to sustain relatively low levels of disease, and remain suitable for Douglas-fir under climate change over the course of this century.