Forest carbon offsets in the United States

Abstract

F orests provide numerous ecosystem services that benefit society. One that is in the forefront is the important function of helping to maintain the carbon balance in the Earth's atmosphere. Growing trees take carbon dioxide (CO2) from the atmosphere and convert it to organic carbon through the process known as photosynthesis. While trees can also release CO2 through decomposition and cellular respiration, healthy growing forests usually have net gains in carbon and act as carbon sinks. Carbon storage of trees is usually measured in CO2 equivalents. Total carbon weight in trees can be computed from dry weight of tree biomass by dividing by 2 as trees are roughly 50% 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 CO2. According to Birdsey (1992), 2.96 × 108 ha (7.31 × 108 ac) of forest ecosystem in the United States stores 1.93 × 1011 t (2.16 × 1011 tn) of CO2 as organic carbon. Of this total, 31% is stored in trees, including stems, limbs, leaves, and roots. The other 59% is found in the soil of forest ecosystems. The carbon storage capacity of trees differs …