Satellite Data Analysis and Ecosystem Modeling for Carbon Sequestration Assessments in the Western United States

The active management of long-term carbon pools in terrestrial vegetation and soils is an important tool for mitigating the rise in atmospheric CO 2 concentrations. This paper demonstrates the use ofremote sensing, climate records, and a vegetation-soil model National Aeronautics and Space Administration―Carnegie-Ames-Stanford Approach to estimate the past and future carbon balance in vegetation and soils. Using the western United States (WUS) as a case study, we describe spatially detailed (<10-km resolution) terrestrial carbon budgets for ecosystems of the Rocky Mountain and Pacific regions of the country. Net primary production increased on a western region-wide basis during the 1990s to 0.9 ± 0.1 Pg C/year, but the total terrestrial sink in all western U.S. ecosystems did not exceed 0.01 Pg C/year between 1982 and 1997. Over the entire period of 1982―1997, the total estimated net ecosystem production (NEP) flux from WUS ecosystems was 1.3 Pg C lost to the atmosphere (1 Pg = 1 billion metric tons). Forested mountain areas of the Cascades, the Sierra Nevada Range, the northern California Coast Range, and the southern Rockies were estimated as the only consistent ecosystem carbon sinks up to 1997. Most of the remaining vegetated (nondesert) lands of the western states were estimated to lose between 50 and 350 g C m ―2 as net ecosystem fluxes were summed over the period 1982―1997. Future climate scenario tests imply major ecosystem carbon losses in the west will continue in all but the most isolated forest areas of the mountain regions. Carbon pools in surface soils and woody litter pools in all WUS ecosystems are estimated currently at 12 Pg C. These baseline carbon pools are likely to become more susceptible to loss under climate model predictions for the western states over the next 50―100 years.