A Process-Based Framework for Predicting Climate-Driven Insect Outbreaks and Their Forest Biogeochemical Impacts

Insect outbreaks have been reported to increase worldwide in association with more frequent   droughts and warming temperatures. Outbreaks of bark beetles and defoliators can cause substantial tree mortality and forest die-off, posing significant threats to carbon sequestration and forest functioning. Climate change can exacerbate such outbreaks by expanding insect habitats, reducing overwinter mortality rates, and enabling multiple generations within a single year. However, the dynamics and potential global impacts of insect outbreaks under climate change remain poorly understood due to the lack of fully coupled terrestrial biosphere models that incorporate both predictive insect population dynamics and their biogeochemical effects. Here, we propose a novel framework to simulate the population dynamics of representative insect types. The model simulates degree-day-based insect development to track transitions among life stages during the growing season, capturing climatic regulation on both phenology and outbreak emergence. This framework successfully reproduced realistic intra-annual population dynamics and temperature-triggered outbreaks at reported bark beetle and defoliator outbreak sites. Idealized future climate simulations reveal increasing outbreak frequency and potential perturbations to forest functioning and carbon storage under warming scenarios. Our work provides a novel approach for predicting insect outbreak risks under future climates and supports improved forest and pest management strategies.