This Special Report examines several key questions relating to
the exchange of carbon between the atmosphere and the terrestrial
pool of aboveground biomass, below-ground biomass, and
soils. Vegetation exchanges carbon dioxide between the atmosphere
and the terrestrial biosphere through photosynthesis and
plant and soil respiration. This natural exchange has been occurring
for hundreds of millions of years. Humans are changing the
natural rate of exchange of carbon between the atmosphere and
the terrestrial biosphere through land use, land-use change, and
forestry activities. Consequently, it is important to examine how
carbon flows between different pools and how carbon stocks
change in response to afforestation, reforestation, and deforestation
(ARD) and other land-use activities.