RustMapper: White Pine Blister Rust Risk Across High Elevation Forests in the Western United States

Background & Summary

White pine blister rust (WPBR), caused by the non-native pathogenic fungus Cronartium ribicola (J.C. Fischer ex Rabh.), is one of the most damaging tree epidemics in North America^1,2. Since its introduction to western North America around 1910 into the Pacific Northwest via infected nursery stock imported from France³, C. ribicola continues to spread and infect new populations of five-needle white pines. The incidence of C. ribicola infection is not uniform on the landscape due in part to the distance from the point of introduction, the biology of the pathogen and hosts, and the environmental conditions required for successful spore production, transport, germination, and infection⁴.

Past efforts to contain the spread of C. ribicola failed⁵; the pathogen is now a permanent resident of North America. While its spread cannot be curtailed, management interventions can reduce the impacts of the disease on pine populations and ecosystem services. WPBR risk or hazard, host species adaptive capacity, and forest health condition of populations and ecosystems can affect the likelihood of treatment effectiveness^{6, 7–8}. Consequently, incorporation of these factors into management frameworks to prioritize limited resources has been recommended^7,9,10. However, reliable geographic projections of current and future WPBR risk still need to be improved for efficient management planning¹⁰.

It has been hypothesized that warmer and drier conditions may reduce the prevalence of WPBR due to the pathogen’s requirement for cool, moist conditions to facilitate infection^{2,11, 12–13}. Consistent with this hypothesis, studies in the Rocky Mountains have found that trees in more arid habitats are less likely to be infected by C. ribicola^14,15. However, for trees already infected in areas experiencing increasing aridity, the likelihood of developing severe symptoms and mortality rises¹⁵. In contrast, Dudney et al. (2021) proposed that increased aridity contributed to a shift in WPBR prevalence uphill in the Southern Sierra Nevada Mountains¹⁶. Additionally, warming temperatures may exacerbate WPBR in moist habitats by extending the growing season, allowing for a longer infectious season¹⁷ and greater canker expansion¹⁸. These findings suggest that understanding WPBR risk will be complex but provide support for customizing landscape restoration strategies by local climatic factors