Tree Line Ecosystems in the Rockies

Introduced species, pests, and pathogens increasingly threaten the sustainability of forests in North America. Invasive, exotic disease may result in the rapid decline of a tree species, thereby impacting ecosystem function; global warming may intensify these effects through heightened disease transmission rates or escalated susceptibility of stressed host species. Whitebark pine, a keystone and foundation species of subalpine and tree line communities of the western United States and Canada, is rapidly declining across most of its range, primarily from damage and death caused by the exotic and invasive disease, white pine blister rust. This decline is beginning to affect both the services and biodiversity of ecosystems located on mountains and around their bases.

Lynn Resler, associate professor of geography, along with colleagues from the University of Colorado-Denver and the University of Iowa, is leading a four-year study funded by the National Science Foundation to investigate how white pine blister rust can alter ecosystem function through the mortality of whitebark pine. “Although whitebark pine is not an economically valuable tree species, it has tremendous ecological worth. Its decline due to white pine blister rust and stress from climate warming will affect mountain animals that rely on the pine seeds for food, decrease biodiversity, and threaten community stability,” said Resler.

A key objective of Resler’s research is to predict the combined impact of climate change and whitebark pine mortality at alpine tree lines. To achieve this goal, Resler and her graduate students are analyzing geographic variations in whitebark pine and blister rust incidence in the American and Canadian Rocky Mountains, and using spatial analysis to model the extent of blister rust infection in whitebark pine at alpine tree lines.

Ultimately, the team seeks to develop a predictive model to determine how the loss of whitebark pine to blister rust will affect alpine tree line and downslope ecosystems. Additionally, they believe natural experiments will uncover how the mortality of whitebark pine from the disease may affect ecosystem function. The results will provide direction for the development of mitigation techniques unique to tree line ecosystems.