Whitebark pine (Pinus albicaulis) forests are declining across most of their range in North America because of the combined effects of three factors: (1) several major mountain pine beetle epidemics that occurred over the last 70 years, (2) an extensive and successful fire exclusion management policy, and (3) extensive infections of the exotic white pine blister rust fungus (Cronartium ribicola). The loss of whitebark pine is serious for upper subalpine ecosystems because it is considered a keystone species across most of its range, producing large seeds that are an important food source for more than 110 animal species.