Collaborative Research: Tree mortality and soil biogeochemical cycling during a northbound spruce beetle outbreak in Alaska

Spruce beetle outbreaks are expanding northward, threatening the vast interior forests of Alaska. These forests provide wildlife habitat, store carbon, and support local communities, recreation, and the regional economy. Spruce beetles are small insects that kill spruce trees by tunneling under the bark. This disrupts the flow of water and nutrients that trees need to survive. The investigators will study why some trees survive beetle attacks while others die, and how forests recover afterward. The results will help predict how outbreaks affect timber and other forest resources, guide efforts to prevent future outbreaks, and show how well northern spruce forests can withstand these attacks as they advance into the Arctic. The project will train students and create teaching materials for primarily undergraduate institutions. The investigators will also give talks at Denali National Park, collaborate with artists to share their findings, and partner with land managers to support forest management in Alaska and beyond. Spruce beetle outbreaks are expanding into high-latitude forests as conditions become increasingly favorable for beetle survival and reproduction. Spruce trees in these forests experience short growing seasons, nutrient limitation, and abiotic stressors such as drought. Relatively large, slow-growing trees growing in dense stands are known to be especially susceptible to attack, but the role of trade-offs between growth, defense, and resource acquisition through ectomycorrhizal fungi remains poorly understood. As infestation progresses, declining carbon transport to roots and ectomycorrhizal fungi is expected to alter fungal communities and carbon and nutrient cycling during forest recovery. This project will capitalize on the intersection of an expanding northward spruce beetle outbreak with a well-established network of long-term ecological research plots in Denali National Park to identify the mechanisms driving tree mortality and belowground ecosystem consequences. The investigators will quantify tree growth and defense traits, ectomycorrhizal associations, stand structure, soil nutrient availability, and understory vegetation using repeated field surveys of beetle attack, dendrochronology, soil respiration, chemistry assays, and DNA sequencing of root-associated fungal communities. Together, these measurements will reveal how carbon allocation trade-offs influence spruce beetle-induced mortality and reshape plant-fungal interactions, belowground biogeochemistry, and post-disturbance forest succession, offering broader insight into how Arctic and other high-latitude ecosystems will respond as this disturbance regime moves north. 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.