Rangelands provide significant environmental benefits through many
ecosystem services, which may include soil organic carbon (SOC)
sequestration. However, quantifying SOC stocks and monitoring carbon (C)
fluxes in rangelands are challenging due to the considerable spatial and
temporal variability tied to rangeland C dynamics, as well as limited
data availability. We developed a Rangeland Carbon Tracking and
Management (RCTM) system to track long-term changes in SOC and ecosystem
C fluxes by leveraging remote sensing inputs and environmental variable
datasets with algorithms representing terrestrial C-cycle processes.
Bayesian calibration was conducted using quality-controlled C flux
datasets obtained from 61 Ameriflux and NEON flux tower sites from
Western and Midwestern U.S. rangelands, to parameterize the model
according to dominant vegetation classes (perennial and/or annual grass,
grass-shrub mixture, and grass-tree mixture). The resulting RCTM system
produced higher model accuracy for estimating annual cumulative gross
primary productivity (GPP) (R2 > 0.6, RMSE < 390
g C m-2) than net ecosystem exchange of CO2 (NEE) (R2 >
0.4, RMSE < 180 g C m-2), and captured the spatial variability
of surface SOC stocks with R2 = 0.6 when validated against SOC
measurements across 13 NEON sites. Our RCTM simulations indicated
slightly enhanced SOC stocks during the past decade, which is mainly
driven by an increase in precipitation. Regression analysis identified
slope, soil texture, and climate factors as the main controls on
model-predicted C sequestration rate. Future efforts to refine the RCTM
system will benefit from long-term network-based monitoring of rangeland
vegetation biomass, C fluxes, and SOC stocks.