Forests in Response to Changing Environments: Understanding the Roles of Nutrient and Disturbance with Computational Models

Forests play a vital role in mitigating climate change by sequestering carbon, conserving biodiversity, and providing other ecosystem services. However, they face significant threats from anthropogenic climate change, land-use changes and subsequential disturbances, which alter the forest dynamics and carbon cycling. This dissertation investigates forest responses to these environmental challenges, focusing on carbon allocation, biomass turnover, and disturbance legacies across diverse ecosystems. The first study explores nutrient fertilization effects on carbon allocation in tropical dry forests. Using the ED2 model and Costa Rica fertilization experiment data, it demonstrates how phosphorus availability shapes carbon allocation to leaves, wood, and roots. The findings highlight the sensitivity of carbon sink estimates to nutrient dynamics, emphasizing the need for refined model representations of nutrient effects. The second study evaluates biomass turnover in Amazonian forests under current and future climates. Through Bayesian calibration and sensitivity analyses, it addresses biases in the ED2 model’s mortality simulations. The study reveals the critical importance of turnover processes in improving biomass projection accuracy under climate change scenarios. The third study examines the legacy effects of Emerald Ash Borer outbreaks on temperate forests in the U.S. Midwest and Northeast. Using the Forest Vegetation Simulator, it identifies long-lasting impacts on forest structure and function, revealing the ecological and management challenges of invasive species. By integrating empirical data with advanced modeling, this research advances the understanding of forest responses to environmental stressors. It underscores the importance of refining models to accurately represent nutrient dynamics, turnover processes, and biotic disturbances, providing valuable insights for predicting and managing forest carbon dynamics under global change.