In the Pacific Northwest, shade-intolerant Coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) and shade-tolerant true fir species (Abies spp.) are experiencing widespread decline and dieback in dry forest ecosystems. Evidence indicates the long-term encroachment of these species into drier areas following decades of fire suppression, coupled with recent droughts, is the primary driver of their decline. Yet, managers struggle to implement effective treatments across forests with different climates, land features and structures due to gaps in our understanding of how these variables influence forest resilience to drought. Improving our understanding of drought resilience is crucial, as effective forest management practices that help trees cope with drought can positively impact forest health, retain the commercial value of trees, and reduce fire exposure risks to communities.

Alex’s project, co-developed with partners from the Oregon Department of Forestry and the USDA Forest Service, aims to help fill these knowledge gaps to inform adaptive management in dry forests. Focusing on southwest Oregon forests, across the Oregon portion of the Klamath ecoregion and the adjacent portion of the Western Cascades ecoregion, Alex will combine wall-to-wall spatial modeling (predicting decline probability across the entire region), tree-ring analysis and direct measurements of plant water stress to understand how climate, topography, forest structure and species traits like shade tolerance interact to influence the resilience of individual trees, as well as populations of trees, to drought. This multiscale approach will reveal how climate, topography, forest structure and species traits influence decline across the landscape.

During his time as an NW CASC fellow, Alex will develop remote-sensing-based models of Douglas-fir and true fir decline, charts of tree growth over time, and collect direct measurements of plant water stress. By identifying trends in tree decline, high-risk areas and the factors that drive vulnerability, this project will assist managers in selecting areas for treatment and setting specific adaptive management targets for increasing ecosystem resilience to drought. Oregon Department of Forestry and Forest Service partners in Southwest Oregon will directly benefit from these tools, which will allow them to identify forests that require direct intervention as well as establish specific targets that will minimize the potential decline of trees in those forests.