Vegetation and biomass dynamics were simulated using the Net Ecosystem Carbon and Nitrogen (NECN) extension, which represents both aboveground processes (growth, mortality, regeneration) and belowground processes (decomposition, soil carbon turnover). The model tracks live biomass, dead organic matter, and soil organic carbon pools, capturing how ecosystem productivity and carbon storage shift under different climate and management scenarios. Thirty-nine tree species and three shrub functional groups were parameterized using California-specific data on growth rates, mortality patterns, and species traits. Each simulation accounts for the influence of temperature, precipitation, and water deficit on productivity, providing detailed estimates of Net Primary Productivity (NPP), Total Ecosystem Carbon, and Net Ecosystem Exchange at annual timesteps from 2001 to 2100.

Disturbance processes, including wildfire and insect outbreaks, were integrated directly within LANDIS-II to create a dynamic feedback between vegetation and disturbance. Wildfire was simulated using the SCRPPLE fire extension, which stochastically models ignition, spread, and severity based on fuels, topography, and weather conditions. Insect outbreaks were represented through the Biological Disease Agent (BDA) extension, which modeled bark beetle and defoliator dynamics in response to drought stress and host density. Together, these modules allow LANDIS-II to represent the complex interactions among growth, mortality, disturbance, and regeneration that shape long-term ecosystem structure and function. Model runs were performed on annual timesteps from 2001 to 2100, using both dynamically downscaled Weather Research and Forecasting (WRF) data from UCLA and statistically downscaled LOCA2-Hybrid datasets from Scripps. Each scenario includes replicate model runs to capture variability.

By combining ecological realism with fine spatial resolution, LANDIS-II model outputs enable researchers and land managers to evaluate how forest carbon sequestration, fuel buildup, and ecosystem resilience evolve under alternative climate and management futures. The model’s outputs, available as gridded data products, support statewide carbon accounting, forest health assessments, and long-term wildfire planning.