The multidimensionality of forest carbon cycling and structure in response to disturbance

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Forests provide food, fuel, timber, recreation and wildlife habitat, and store large amounts of carbon. However, the sustainability of these valuable goods and services is threatened by insects that defoliate and often kill trees. This project uses field experiments and computer models to investigate how forest growth and carbon uptake are affected by variable levels of tree mortality caused by wood boring insects. Specifically, the research studies whether initial changes in forest growth and carbon sequestration following disturbance can be used to predict longer-term responses at timescales meaningful to forest and land managers; what biological and physical characteristics enable forests to recover from disturbance; and what information needs to be included in computer models to predict how forests will respond to insect pests. The project engages a diverse team of undergraduate, post-baccalaureate, and graduate students, providing training that is applicable to careers in forest and conservation management, environmental science and policy, data management, and computer coding and model simulation. The project also produces freely available educational resources for upper-level college instructors, professional ecologists, land managers, and commercial foresters. Moreover, project data and the field experiment itself- located at a field station in Michigan- serve as openly shared resources for onsite education and research training for hundreds of students, researchers, educators, and community members annually. This project uses the Forest Resilience Threshold Experiment (FoRTE), which was established in 2018 at the University of Michigan Biological Station to examine how and why forest carbon cycling processes will respond to a range of disturbance severities caused by insect pests and pathogens. The replicated, 8-hectare experiment includes zero (control), 45%, 65%, and 85 % levels of gross defoliation and incorporates two disturbance types. Leveraging FoRTE’s expansive axes of disturbance severity, site productivity, and vegetation composition, the project uses observations to ask: (1) Do trade-offs exist between dimensions of carbon cycling stability, (2) To what extent are forest composition, structure, and net primary production linked during disturbance response, and (3) What degree of model complexity is required to simulate observed carbon cycling stability across the full disturbance-response cycle? This study experimentally and computationally simulates the carbon cycling consequences of newly emerging disturbance patterns. The experiment adopts a novel stability theoretical framework, previously applied almost exclusively to populations and communities, to assess carbon cycling responses to disturbance severity and type.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.