Future climate may intensify, not alleviate, disease stress on high elevation white pines

Prioritizing areas for limited resources has long been a challenge in forest health management, especially for High-5 (high-elevation, five-needle) white pine species across western North America. Although restoration strategies underscore the need for robust information on white pine blister rust risk, managers have lacked effective tools to project against that risk across space and time. 

Photo Credit

Forest Service photo by Anna Schoettle

Two limber pine trees in decline due to white pine blister rust in southern Colorado. The tree on the left has dead branches, called flagging, caused by white pine blister rust cankers on those branches.  The cankers on the tree on the right have grown into the main stem and girdled and killed the tree.

This need has also been expressed by the U.S. Fish and Wildlife Service as they prepare the Recovery Plan for whitebark pine, listed under the ESA in 2023.

New models bring together current knowledge of the biophysical factors that drive white pine blister rust infection and spread, combined with nearly 30 years of field data collected by forest health professionals. Using this integrated approach, Forest Service researchers have developed the first current and future west-wide projections of blister rust risk for High-5 distributions across the western U.S.

White pine blister rust is widespread, but many suitable high‑elevation areas have not yet been infected, though our projections show that most High‑5 pine distributions will face increasing risk throughout this century.

Contrary to earlier assumptions, future climate isn't expected to hamper conditions favorable to this disease. These findings highlight the need for both proactive management in areas of increasing risk and continued restoration where the disease is already present to sustain populations, ecosystem function, and watershed protection.

The need for a forward-looking forecast has shaped the first large-scale risk model for white pine blister rust across the western United States. Susceptible species in the west include “High-5 pines” like the endangered whitebark pine, limber pine, foxtail pine, southwestern white pine, and the charismatic two bristlecone pines (Great Basin and Rocky Mountain). 

This research can help land managers plan more effectively across both space and time and provides guidance on critical questions such as: 

• Where is the disease likely to occur in the future?
• How likely is it to spread to a particular area?
• Are conditions primed for new waves of infection?
• Where, if anywhere, are high-elevation five‑needle pines relatively protected?

Models like these help identify factors that may be driving the patterns we see on the landscape. Using these models, managers can pinpoint patterns in white pine blister rust risk across the High‑5 ranges. This framework can also support future research by showing how information from past conditions and current spatial patterns can be used to better understand and anticipate future change.

Manangers can compare species and locations at a scale far beyond individual forests or regions. With limited resources, these insights can be used to prioritize where to focus efforts to maintain healthy populations and restore areas already affected. In addition, this project is the first of it's kind to assess the risk of white pine blister rust for the long-lived iconic bristlecone pines species and has revealed that their distributions are vulnerable.