MSB-ECA: A generalized framework for modeling the impacts of forest insects and pathogens in the Earth System

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Abstract: MSB-ECA: A generalized framework for modeling the impacts of forest insects and pathogens in the Earth SystemForest insects and pathogens are global agents of ecosystem disturbance. In the United States, tree stress and mortality from insects and pathogens creates billions of dollars in costs for U.S. municipalities and individual property owners. The interactions between insects and pathogens and other disturbances, such as climate change, are highly uncertain, but in many cases climate change is expected to increase insect and pathogen activity. This project will develop a framework to simulate and forecast the impacts of forest insects and pathogens through a generalized method that accurately captures the large diversity of their impacts. This framework will be used to simulate the potential impacts of insect and pathogen outbreaks in forests across the continental U.S. and to investigate the specific impacts of two invasive insects ? gypsy moth and hemlock woolly adelgid ? in the eastern U.S. A key benefit of this research is that it will improve the ability to simulate future impacts of insects and pathogens on forests in combination with other disturbances like drought, heat waves, and extreme rainfall events. This research will also increase the diversity of the U.S. STEM workforce by training undergraduate women in cutting-edge quantitative methods. Future feedbacks between forest insects and pathogens, forests, and climate change are not well understood at regional to continental spatial scales, due in part to the absence of the processes controlled by insects and pathogens within Earth System models. This research proposes a generalized framework in which impacts of insects and pathogens on plant physiology are scaled up to ecosystem-level processes that can be integrated into Earth System models. With this framework, this research tests three hypotheses regarding the response of forests to insects and pathogens: 1) at low intensities, insects and pathogens increase tree diversity, increase forest carbon storage, and increase water cycling, but at high intensities insects and pathogens create large-scale mortality; 2) the ability of insects and pathogens to impact a wide range of host species will be less likely to shift forest tree species composition but more likely to impact carbon and water cycling; 3) insects and pathogens that create a continuous stress, rather than periodic irruptions, are more likely to initiate impacts that are amplified by climate change. These hypotheses will be tested with theoretical modeling experiments across the continuous U.S. and with a second set of modeling experiments focused on two invasive insects in the eastern U.S.: 1) periodic irruption of the generalist, defoliating gypsy moth, and 2) slow and continuous stress from the species-specific, phloem-feeding hemlock woolly adelgid. Rather than modeling insects and pathogens as direct agents of mortality, this framework will more accurately simulate changes in individual host tree physiology and resulting changes in ecosystem processes. To facilitate the incorporation of this framework into other Earth System models, this research will develop two open-source training modules. The proposed research will also help to develop a diverse and competitive STEM workforce by training undergraduate women in research that uses advanced computational methods and develops skills in scientific communication.