Carbon‐Nutrient Interactions Under Insect Disturbance Simulated by the Land‐Surface Model QUINCY 21edff48

Abstract

Insect outbreaks significantly impact tree mortality and carbon‐nutrient cycling in forest ecosystems, yet most terrestrial biosphere models do not represent insect disturbances due to the complexity of nutrient processes and limited data. To address this gap, we implemented a new insect impacts module in the QUINCY (Quantifying Interactions between terrestrial Nutrient Cycles and the climate system model) model, version 21edff48. This new module represents, for the first time, impacts of bark beetle and defoliator insects on forest structure and functioning in a fully‐coupled carbon, nitrogen, and phosphorus framework, providing new insights into nutrient dynamics induced by insect outbreaks. To achieve this, we represent key processes such as tree mortality, snag decay and larvae feeding effects on nutrient cycling pathways. Model evaluation against observations at disturbed forest sites captured shows agreement with the direction and magnitude of anomalies in carbon, water and energy exchanges, and nutrient cycling during and following disturbances. Idealized post‐disturbance simulations revealed that phosphorus limitation is a key factor influencing vegetation recovery, with CNP runs simulating longer recovery for both bark beetle and defoliator disturbances than C or CN runs. These outcomes are governed by the balance between enhanced growth of newly established trees, changes in nutrient acquisition, and nutrient losses through leaching, highlighting that nutrient‐disturbance interactions critically shape post‐disturbance ecosystem trajectories. Our new implementation of insect disturbance impacts advances in understanding of insect disturbance effects on forest biogeochemistry and improves the prediction of forest responses to projected changes in insect disturbances under climate change.