carbon weight in trees can be computed from dry weight of tree biomass by dividing by 2 as trees are roughly fifty percent carbon based on dry weight. Carbon weight can then be converted into CO2 weight by multiplying by 3.67, based on the molecular weights of carbon and carbon dioxide. According to Birdsey (1992), 731 million acres of forest ecosystem in the U.S. stores 192.7 billion metric tons of CO2 as organic carbon. Of this total, 31 percent is stored in trees, including stems, limbs, leaves, and roots. The other 59 percent is found in the soil of forest ecosystems. The carbon storage capacity of trees differs by tree species, tree age, geographic location, and management intensity. The annual increase in carbon storage in a well-stocked forest of common commercial tree species in the U.S. varies from 1 to 5 or more metric tons of CO2 per acre per year. Since carbon storage in trees is proportional to tree biomass weight, traditional silvicultural practices intended to increase volume for wood products are compatible with increasing carbon storage capacity of trees. As such, managed stands will store carbon at a faster rate than slower growing natural stands of the same species (Birdsey, 1992). When trees reach maturity and volume growth slows or stops, additional carbon sequestration no longer occurs. Because of the effectiveness of forests as carbon sinks, carbon stored in forests is often accepted as offset credits in carbon emission control systems. Today's carbon market in the U.S. is a developing, voluntary market since there is no national, regulatory greenhouse gas reduction scheme. However, many local, state, and regional systems and registries for reducing greenhouse gas emission exist, including the Regional Greenhouse Gas Initiative in several northeastern states, the Department of Energy National Voluntary Reporting of Greenhouse Gases Program (the 1605(b) program), and the California Climate Action Registry. These systems and registries lead to opportunities for carbon credits from forestry carbon offset programs.