Regional differences in carbon source-sink potential in the US

We used the dynamic vegetation model MC1 to simulate the change in carbon storage potential under historical conditions (1895-1994) in the 6 regions of the conterminous USA delineated for the USGCRP National Assessment. The largest variations occur in the Midwest where large fire events (1937, 1988) affect vegetation biomass. The Southeast shows decadal-type trends and alternates becoming either a carbon source (1920's, 1940's, 1970's) or a sink (1910's, 1930's, 1950's). The drought of the 1930's is most obvious in the creation of a large carbon source in the Midwest and the Great Plains. The two most western regions and the northeast show the smallest amplitudes in their variations. Projections into the future using the CGCM1 climate scenario show the Northeast becoming mostly a carbon source, the Southeast becoming the largest carbon source in the 21st century, and the two western-most regions becoming arbon sinks in the second half of the 21st century. Regional trends in C storage under historical conditions show an increase in soil organic matter with time except in the Midwest which starts loosing carbon in the 1900's but starts recovering it by the 1970's. The Pacific Northwest shows a less pronounced decline in soil C but that continues through the 1980's. Projections into the future show increases in soil organic matter in the Great plains and the two western-most regions, decreases in the Midwest and the Northeast,and a huge decline in the Southeast soil carbon levels with respect to the 1895 level.