Mapping climate and disturbance refugia for conservation of whitebark pine

Abstract

Whitebark pine (Pinus albicaulis Engelm.) is a keystone species of montane ecosystems in western North America, where it plays an important role supporting wildfire and other vegetation. It is experiencing a rapid decline primarily due to white pine blister rust (Cronartium ribicola J.C.Fisch.), an invasive fungal disease, as well as other threats including increasing wildfire severity and frequency as well as climate change which exacerbates these threats. To protect this iconic tree species, land managers need to understand how climate influences these threats across the species' range and identify locations where conservation efforts are likely to succeed. My research analyzes climate impacts on threats to whitebark pine across multiple spatial scales. Broad-scale models are used to predict wildfire ignition danger and white pine blister rust infection hazard across large areas of the western United States. At fine scales, I used a high-resolution water balance model to identify small, favorable planting sites that may offer protection from projected drought stress for seedlings. My findings reveal that climate strongly influences both wildfire ignition danger and white pine blister rust infection, with specific moisture and temperature conditions promoting these threats. Projections indicate that climate change will generally increase the risk for these disturbances, although patterns of this change vary geographically. The high-resolution water balance analysis reveals that despite climate projections showing extreme drought, small-scale microrefugia exist where local terrain and soil features could provide protection from drought stress. This work provides valuable, climate-informed tools for whitebark pine conservation. The models and maps can help land managers identify areas projected to face lower long-term risks from both wildfire and white pine blister rust. These refugia can be targeted for conservation actions, such as planting disease-resistant seedlings, improving the likelihood of successful establishment and survival, thus enhancing efforts to conserve this iconic species in a changing climate.