Ecological carbon stores on Department of Defense (DoD) lands are integral to natural infrastructure, contributing to land resilience and reducing long-term restoration costs, but their dynamics are highly sensitive to landscape changes such as drought, flooding, salinity, and silvicultural treatment. Tools for anticipating the evolving effects of these changes over timescales relevant for management action planning both alone and when combined do not currently exist. The objective of this project is to build and test a new modeling capability to enable mechanistic evaluation and reduce forecast uncertainty of carbon uptake and storage under disturbance and management scenarios on DoD lands.

The modeling capability will be based on the unique, three-dimensionally explicit, meter-scale representation of ecosystems that has been developed in Los Alamos National Laboratory’s R&D100-winning HIGRAD/FIRETEC model and associated SERDP-funded Disturbance Response Model. We hypothesize that explicitly simulating the three-dimensional heterogeneity of vegetation structure at meter scales over landscape scales is required for reducing uncertainty in predicting impacts of potential environmental stress and silvicultural treatments on ecosystem carbon uptake because stand structure and tree arrangement (i.e. randomly distributed, versus uneven age clumps versus single aged/sized classes) influence energy and water fluxes as trees compete for light, water, and collectively alter their micro-habitat. The HIGRAD/FIRETEC model currently includes presentation of individual trees and their coupling to the atmosphere through aerodynamic drag and convective heat transfer. It also includes a spatially explicit model that calculates incoming solar radiation through the explicitly resolved, three-dimensional canopy to quantify fuel energy balance. It can obtain soil moisture estimates from PARFLOW soil hydrology model, but it does not have an explicit plant physiological representation of photosynthesis, transpiration and plant stress responses. 

To create and test the new modeling capability, the project team will conduct the following tasks: 

1. Model development: Implement a spatially-explicit (meter scale) plant carbon uptake and stress response model into HIGRAD/FIRETEC using existing plant physiological drought response modeling approaches at the leaf and xylem scale.
2. Stress response presentations, model parameterization and validation: Conduct field measurement campaigns, and controlled experiments, and combine their results with existing fieldscale carbon flux data from Ameriflux, National Ecological Observatory Network and Long Term Ecological Research-networks to create representations for plant carbon responses to salinity and flooding. Parameterize and validate the plant carbon uptake model for arid Southwest conifer forests, mesic Southeast conifer forests, and East coast wetlands similar to ecosystems on DoD lands.
3. Model runs, scenarios, and uncertainty and sensitivity analyses: Estimate how much uncertainty in the simulated carbon fluxes arises from uncertainty in the basic leaf and plant hydraulic parameters and their responses to stress. Use the new HIGRAD/FIRETEC modeling capability to evaluate and identify critical processes, thresholds and stand structure feedbacks that govern the combined impacts of landscape management (or lack of management) and drought, salinity and flooding stress on ecosystem carbon uptake for scenarios selected with help of experts for the targeted DoD sites. 

The project team will demonstrate and validate a novel, stand-level modeling capability for the combined potential impacts of natural stressors and forest management practices on carbon uptake and storage for ecosystems found on DoD lands, thereby creating new knowledge about how drought, salinity, and flooding affect vegetation carbon uptake. This improved understanding will enable more efficient and informed forest management decisions by predicting carbon storage impacts at actionable scales and resolutions, supporting strategic stewardship of DoD natural resources. (Anticipated Project Completion - 2028)