Doctoral Dissertation Research: Assessing Regeneration Niche Limitations to Upslope Migration of Subalpine Forests

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This doctoral dissertation research project will examine how tree regeneration in subalpine forests is being influenced by changes in climate and wildfire activity. By collecting and analyzing extensive field data on factors affecting tree seedling establishment and survival, the doctoral student will identify threats to subalpine forest resilience. The project will identify altered regeneration patterns in forests, thereby improving capabilities for forecasting broad-scale changes in subalpine forest sustainability and for understanding impacts on carbon storage and cycling, hydrologic processes, and ecosystem services. Because the study will be conducted in the kinds of forests that are widely distributed across the western United States, research results will have wide-ranging utility. By elucidating how the relatively fast pace of recent warming affects subalpine tree regeneration, this project will address societal needs for understanding and adapting to changes in forests and the ecosystem services they provide. Project findings will help land managers to develop appropriate plans for climate adaptation and to evaluate ecosystem vulnerability to climate changes. To communicate these research findings to land managers and other stakeholders, the investigators will host workshops that address how subalpine forests respond to changing temperatures regimes and increased disturbance by wildfire and bark beetles. The workshops also will facilitate discussions about adaptation strategies for likely forest changes expected under changing climatic and environmental conditions. The student and his advisor will develop curriculum materials and will lead field trips for K-12 education at underserved schools, and they will mentor undergraduate students as research assistants through established teaching and advising programs. As a Doctoral Dissertation Research Improvement award, this award will provide support to enable a promising student to establish a strong independent research career.Global distributions of tree species are closely related to climate conditions. As temperatures continue to increase, the suitable habitat for tree species is projected to shift upslope. To compensate for lost habitat at the lower elevation limit, subalpine tree species are expected to migrate upslope to maintain existing populations. To migrate upslope, trees must first produce sufficient seed, and seeds must arrive in suitable habitats for germination and survival. As part of this project, the doctoral student will measure these reproductive processes and link them to climatic and other environmental factors to build models assessing the feasibility of upslope migration of tree populations and the sustainability of existing subalpine forests. The project will address the following questions: (1) Will increasing fire frequency prevent tree populations from reaching the size and ages required for adequate seed production to maintain future forest cover? (2) As temperatures rise and moisture availability declines, is upslope migration of tree populations and the resilience of existing subalpine forests limited by seed production and lack of suitable habitats for seedling germination and survival? (3) How has the establishment of tree seedlings (over the last 80 years) been influenced by variability in climate? The student will use extensive field data collected from past disturbances and the natural topoclimatic variation across the ranges of subalpine tree species to mimic change in climatic conditions. He will quantify the long-term response of key regeneration processes like reproductive maturity, seed availability, and microsite limitations in response to climate variability and to changes in disturbance regimes. He then will link fine-scale field results to broad-scale spatial datasets to parameterize and implement a cross-scalar spatial model that will evaluate key limitations to seedling recruitment over a range of environmental change projections.