Unprecedented outbreaks of mountain pine beetle are occurring in Greater Yellowstone Ecosystem (GYE) whitebark pine. A warming climate has resulted in a fundamental regime shift that has allowed sustained outbreaks in high-elevations habitats that were previously too cold, resulting in extensive whitebark pine mortality. These forests provide critical ecological services ranging from wildlife habitat to hydrologic function. The regional impact of the loss of this critical keystone species in these remote habitats will have large scale ecological impacts.
We first describe a temperature driven mountain pine beetle life-history model based on life stage specific developmental rate data. Field validation studies verified the ability of this model to predict seasonal life-history events. Simulations with this model reviled thresholds for regime shifts as mean annual temperature was gradually increased. Mathematical analysis confirmed these results, and provided a theoretical basis for analysis of annual temperature cycles. Studies using these results indicated the potential for expanded MPB outbreak activity in high-elevation, whitebark pine habitats for temperature increases within the range predicted by the IPCC reports for “business as usual” CO2 scenarios.
Predictive capabilities were expanded to the landscape level by incorporating the model within the BioSIM modeling framework. MPB outbreak risk maps were then generated for a variety of sensitive landscapes, including the GYE. These simulations indicated that large areas of whitebark pine habitat would be at high risk by 2030. However, widespread mortality began to be observed by 2004. Due to a combination of the spatial extent and administrative complexity of the GYE, and the remoteness and ruggedness of high-elevation habitats, the actual extent of mortality remained unknown.
Results/Conclusions
Motivated by the fact that critical management decisions were being made based on inadequate information, we imitated a Landscape Assessment System (LAS) designed to assess the cumulative impact of MPB in GYE whitebark pine. Briefly, the LAS approach uses over-flights to capture geo-tagged oblique aerial photography at the sub-watershed level. Within a GIS platform the aerial photos are assigned a mortality rating based on an outbreak classification system that rates the intensity of mortality ranging from zero, (no unusual MBP activity) to six (the residual gray forest). Results from this study indicate that 94% of GYE whitebark pine have suffered some level of recent MPB mortality, and of this, approximately 50% has mortality levels that begin to impact ecological services provided by this important species. Ecological implications of these results will be discussed.
