Restoring whitebark pine in the face of climate change
Whitebark pine forests are declining across most of their range in North America because of the combined effects of mountain pine beetle outbreaks, fire exclusion policies, and the exotic pathogen Cronartium ribicola, which infects five-needle white pines and causes the disease white pine blister rust. Predicted changes in climate may exacerbate whitebark pine decline by (1) accelerating succession to more shade tolerant conifers, (2) creating environments that are unsuitable for the species, (3) increasing the frequency and severity of mountain pine beetle outbreaks and wildland fire events, and (4) facilitating the spread of blister rust. Yet, whitebark pine tolerates a variety of stressful conditions and has the broad genetic diversity to adapt to changes in climate and disturbance. The ongoing decline in this high-elevation tree species poses serious consequences for upper subalpine and treeline ecosystems and, as a result, whitebark pine is a candidate species for listing under the Endangered Species Act. The large, nutritious seeds produced by this pine are an important food for many bird and mammal species, such as the endangered grizzly bear. Because more than 90 percent of whitebark pine forests exist on public land in the United States and Canada, a rangewide whitebark pine restoration strategy was developed to coordinate and inform restoration efforts across federal, state, and provincial land management agencies. This restoration strategy, however, failed to fully address the projected effects of climate change on whitebark pine restoration efforts and existing populations. In this study, we present guidelines for restoring whitebark pine under future climates using the rangewide restoration strategy structure. General restoration guidelines considering effects of climate change are given for each of the strategy’s guiding principles: (1) promote resistance to blister rust, (2) conserve genetic diversity, (3) save seed sources, and (4) employ restoration treatments. We then provide specific guidelines for each of the strategy’s actions: (1) assess condition, (2) plan activities, (3) reduce disturbance impacts, (4) gather seed, (5) grow seedlings, (6) protect seed sources, (7) implement restoration treatments, (8) plant burned areas, (9) monitor activities, and (10) support research. We used information from two sources to account for climate change impacts on whitebark pine restoration activities. First, we conducted an extensive and comprehensive review of the literature to assess climate change impacts on whitebark pine ecology and management. Second, we augmented this review with results from a comprehensive simulation experiment using the spatially explicit, ecological process model FireBGCv2. This modeling experiment simulated various climate change, management and fire exclusion) scenarios. We also ran FireBGCv2 to evaluate the effects of specific rangewide restoration actions with and without climate change. We analyzed two simulated response variables (whitebark pine basal area, proportion of the landscape dominated by whitebark pine) to explore which restoration scenarios are likely to succeed. Our findings indicate that management intervention actions such as planting rust-resistant seedlings and employing proactive restoration treatments, can return whitebark pine to the high mountain settings of western North America to create resilient upper subalpine forests of the future. The report is written as companion guide to the rangewide restoration strategy for planning, designing, implementing, and evaluating fine-scale restoration activities for whitebark pine by addressing climate change impacts.
