The nonnative pathogen Cronartium ribicola, the cause of the lethal white pine blister rust (WPBR) disease, is spreading through limber pine (Pinus flexilis) and Rocky Mountain bristlecone pine (P. aristata) forests of the southern Rocky Mountains (USA). An integrated regional program - the Proactive Strategy - is characterizing the infestation and gaining ecological and genetic knowledge of these less well studied ecosystems. This knowledge will provide the science foundation for early interventions to mitigate the development of ecological impacts to the high mountain headwater ecosystems (Burns et al. 2008; Schoettle and Sniezko 2007; Schoettle et al., this proceedings, The Proactive Strategy: Preparing the Landscape for Invasion by Accelerating the Evolution of Resistance). Identifying and developing planting material with genetic resistance to WPBR, and understanding its field performance, is essential for managers to sustain these forests into the future.