High elevation white pines and the headwater ecosystems they occupy are threatened by the non-native lethal disease white pine blister rust (WPBR). Many ecosystems in the West are already affected while other ecosystems are not. The landscapes however, are susceptible to invasion and the continued spread of the pathogen over time is inevitable. Without early intervention, we have seen WPBR cause high mortality in five-needle pine species in the Northern Rocky Mountains. In order to develop mitigation strategies and guidelines and to time their implementation for maximum efficacy, we must understand population outcomes of the pending invasion and the effects of management on those dynamics.
High elevation pine forests are valued by people for their aesthetics and longevity as well as their ecosystem services. These pines often define the very altitudinal limits of tree growth and help capture snow and mediate its melt at the headwaters of western Northern American watersheds. Their large seeds also serve as food for many animals that play important roles in the foodchain of high mountain wildlife.
We developed a mechanistic model to understand the population dynamics of WPBR infection and stand structure under different scenarios. The model demonstrated the important role of managing regeneration and competition to the sustainability of the pine populations, especially at low infection rates. The model also demonstrated that disease resistance selection is occurring for trees of all ages. This helps explain stand structure patterns observed in the field. In addition, we applied a novel mathematical application that enables assessment of key parameter behavior in the management-relevant first 100 years after disease introduction.
Our modeling work highlights the importance and effectiveness of timely management of stand structure to mitigate impacts by WBPR. It also demonstrates that management of stand structures across the landscape before or early in the WPBR invasion-timeline can have long-lasting beneficial effects on the sustainability of pine populations in the presence of WPBR. The model provides insight into possible outcomes of management options by reducing uncertainty and improving trade-off analysis and manager decision-making. This project is one component of the early intervention approach, known as the Proactive Strategy, which was awarded the Forest Service - National Forest System Excellence in Invasive Species Innovative Control and Management Award in 2011.