Spatially explicit projections of land use and carbon dynamics in the conterminous United States: A new approach linking the LUCAS and CBM-CFS3 models

Abstract:

The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) provides a robust and flexible framework which has been widely used to provide estimates of carbon storage and flux in forest ecosystems for numerous countries. The CBM-CFS3 is a spatially referenced model, operating at the forest management unit scale with unique parameterization across combinations of jurisdictional boundaries, ecozones, and forest types. The Land Use and Carbon Scenario Simulator (LUCAS) is a spatially explicit model designed to explore how alternative scenarios of land use and land cover change impact ecosystem carbon balance. Like the CBM-CFS3, LUCAS can be parameterized using combinations of multiple spatial stratifications while also producing spatially explicit maps of LULC and carbon stocks and fluxes.

This research describes a new approach to estimating land use and land cover change and ecosystem carbon dynamics by linking the CBM-CFS3 and LUCAS models. We used the CBM-CFS3 model to generate a series of carbon stock estimates by age for 28 forest type-groups in the conterminous United States. Next, we developed a LUCAS package which parameterizes the LUCAS stock-flow model with carbon turnover rates from CBM-CFS3. Additionally, we incorporated spatially explicit climate projections to modify the turnover rates of dead organic material and the net primary productivity of vegetation. The LUCAS model’s STSM was parameterized using data from remote sensing-based assessments while future scenarios were based on a combination of empirical data and projections associated with global change scenarios.

Results show that at the plot scale, the method can reliably produce carbon stock and flux estimates consistent with those produced by CBM-CFS3 alone. The linked LUCAS-CBM approach provides the added value of being able to easily incorporate alternative scenarios of LULC change to produce spatially explicit maps of carbon dynamics. For this initial project, we used biomass expansion factors and carbon turnover rates from the CBM-CFS3 model. For some forest types and ecosystems found in the conterminous United States, this meant using a similar species type or ecozone. Future work should include development of unique parameters for U.S. forests.