Each year, as forests grown and increase their biomass, they absorb carbon from the atmosphere and store it in plant tissue. This process is known as carbon sequestration.
Despite contant exchanges of carbon between forest biomass, soils, and the atmosphere, a large amount is always present in leaves and woody tissue, roots, and soil nutrients. This quantity of carbon is known as the carbon store.
Carbon sequestration and storage slow the rate at which carbon dioxide accumulates in the atmosphere and mitigate global warming. Forests sequester and store more carbon than any other terrestrial ecosystem, and constitute an important natural defense against climate change.
The following summarizes key findings of the PAGE study regarding conditions and trends in the global carbon cycle of forest ecosystems, as well as the quality and availability of data.
Conditions and trends
- Forest soils and vegetation store about 40 percent of all carbon in the terrestrial biosphere, more than any other ecosystem.
- Globally, more carbon is stored in forest soils than in forest vegetation. Boreal forests are especially rich in soil carbon, while tropical forests probably store more in their vegetation.
- Regrowth of forests in the Northern Hemisphere may account in part for the increasing terrestrial sink that absorbs some of the carbon dioxide emissions released by fossil fuel combustion. However, land use change, primarily tropical deforestation, currently releases an estimated 1.6 billion tons of carbon to the atmosphere each year, equivalent to 25 percent of emissions from fossil fuel combustion.
- Globally, deforestation far exceeds regrowth. The world’s forests are currently a net source of carbon.
Information status and needs
- Uncertainty still exists over rates of carbon sequestration, carbon stores, and the size and location of the terrestrial “missing carbon sink.”
- Improving information is available from local and regional studies on carbon stores in different vegetation types but a variety of measurement methodologies used yields conflicting results.
- Many more soil samples are required globally for more accurate determination of soil carbon stores.
- Better information is needed on carbon sequestration rates at the site-specific level to provide an adequate basis for calculating carbon offsets achievable through afforestation programs under climate mitigation programs.
Quality and availability of data
PAGE measures and indicators
Data sources and comments
Total carbon stored in forests (tons) Olson, J.S., J.A. Watts, and L.J. Allison. 1983. “Carbon in Live Vegetation of Major World Ecosystems.” Report ORNL-5862. Oak Ridge, Tenn: Oak Ridge National Laboratory.
Global estimates of carbon in above and below ground live vegetation, modified by EDC and WRI (USGS/EDC, 1999). Soil carbon estimates based on ISRIC-WISE global dataset of derived soil properties (Batjes, 1996). Both datasets are coarse but globally consistent.
