Modeling of Management Impacts On Carbon Dynamics In Orchards and Vineyards In the U.S.

COMET-VR (Voluntary Reporting Carbon Management Tool) is a web-based tool that provides estimates of carbon sequestration and net greenhouse gas (GHG) emissions for farms and ranches in the U.S.  The first version of COMET-VR was designed to estimate greenhouse gas emissions from annual croplands, hay, pasture and rangelands, but did not include perennial woody croplands.  Though perennial woody croplands, such as orchards and vineyards, represent a relatively small area compared to annual croplands at the national level, these crops are very important in certain regions of the US and may have GHG mitigation potential in those regions.  Because of this, COMET-VR 2.0 was developed to incorporate the main orchard and vineyard crops in the U.S. and provide estimates of GHG emissions from soils and woody biomass.  Modifications were made to the Century Ecosystem Forest Submodel to accommodate the unique characteristics of orchard and vineyard species, as well as management practices specific to orchards, such as pruning, thinning, groundcover management, and fruit harvest.  The model was then tested for the limited number of experimental sites that provided measurement data for woody biomass and soil organic carbon (SOC).  Modeled versus measured estimates for woody biomass were generally good (y=1.2x, R²=0.65), with variability due largely to species cultivar and rootstock.  Only one experimental site provided soil organic matter data, and simulated SOC stocks were within 500 g C m^-2 of the observed values, depending on treatment.  The modified model was incorporated into the COMET system, as well as management practices associated with each orchard or vineyard type that were dominant in each region and have an impact on GHG emissions.  Simulations of different management scenarios were also conducted for dominant orchard and vineyard crops, to evaluate the potential role of these crops in GHG mitigation regionally.