Ecological Disaster or the Limits of Observation? Reconciling Modern Declines with the Long-Term Dynamics of Whitebark Pine Communities

The history of whitebark pine (Pinus albicaulis) forests over the past century exemplifies modern environmental change and the particular challenges faced in reconciling the scales of human observation with long-term ecological changes. A number of factors are implicated in driving observed declines in whitebark pine populations including fire suppression, climate change, the exotic pathogen Cronartium ribicola and associated white pine blister rust, and mountain pine beetle (Dendroctonus ponderosae) outbreaks, yet the actual effects of these factors vary widely across the range of whitebark pine that encompasses considerable environmental heterogeneity. Furthermore, the specific effects of these agents are difficult to isolate or predict in a forest type where disturbance regimes and succession operate on scales of centuries rather than decades. The resulting situation is highly complex, yet the urgency for restoration in some areas is leading to generalizations elsewhere that do not always account for the diversity of forests considered as whitebark pine communities. Our research reviews the current state of knowledge on the biogeography, disturbance regimes, and mechanisms of decline in whitebark pine communities. We then use an expanded temporal perspective based on dendroecological case studies to critically assess the potential effects of fire suppression in whitebark pine communities and the ecological relationship between whitebark pine and mountain pine beetle. Based on our findings, it appears that fire suppression is not the ubiquitous factor leading to whitebark pine declines, as often implicated in the published literature, and that whitebark pine may be well adapted to recover following mountain pine beetle outbreaks in areas that have not been impacted too severely from white pine blister rust.