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Carbon Components
Where is there carbon in the forest?
Plants remove carbon (as CO2) from the atmosphere through the process of photosynthesis and store it in plant tissue. Until this carbon is cycled back into the atmosphere, it resides in one of a number of “carbon pools.” These pools include (a) above ground biomass (e.g., vegetation) in forests, farmland, and other terrestrial environments, (b) below ground biomass (e.g., roots), and (c) biomass-based products (e.g., wood products) both while in use and when stored in a landfill. Carbon can remain in some of these pools for long periods of time, sometimes for centuries. An increase in the stock of sequestered carbon stored in these pools represents a net removal of carbon from the atmosphere.
How do C registries identify C pools?
Carbon registries typically segregate a number of C pools within a forest that can be identified and quantified (Table 2). These carbon pools are categorized in a variety of ways but typically include many of the same components. In many cases carbon is split into above and belowground components with aboveground being everything growing on top of the forest floor. The forest floor (often referred to as forest litter, the litter layer, or forest duff) is typically grouped with the belowground components of mineral soil C and roots (including both fine and coarse roots). The term biomass connotes live material so a few dead biomass components are often specifically mentioned as standing dead or lying dead. The lying dead material is also further referred to as coarse woody debris (CWD) or downed woody debris (DWD).
Total forest C (Tc) is then simply the summation of aboveground (Ac), belowground (Bc), soil (Sc), and litter (Lc) carbon. 
The net change in each of these pools summed over time, either in response to natural succession or some management activities, will determine whether the forest is accumulating or losing C.
Table 2: Forest carbon pools present in C registries
| Category | Carbon Pool |
| Aboveground | Overstory trees Understory trees and shrubs Groundcover: Herbaceous, grass, woody |
| Belowground biomass | Forest Floor Mineral soil organic C Roots |
| Dead Biomass | Standing Dead Biomass Lying Dead Wood |
| Harvested wood | Wood products |
What C pools need to be estimated for carbon registries?
Registries differ in the total number of these pools that are required or are optional in the proposed registry. If required, a landowner would need to quantify the amount of carbon in the pool according to the methods outlined in the registry. If optional, a landowner will need to assess the likelihood that the optional pool can substantial increase the carbon credits available for sale.
Table 3: Forest carbon pools required or optional in C registries
| Entity | Required pool | Optional |
| DOE 1605b | None-this protocol just has suggested guidelines | Aboveground Live trees Belowground roots of live trees Tree seedlings Shrubs, herbs, forbs, grasses Standing dead trees Down dead wood Stumps and dead roots Fine woody debris Litter Humus Soil carbon wood in products |
| CCAR | Aboveground tree biomass Standing dead biomass Lying deadwood | Herbaceous understory and shrubs Soil Litter and duff |
| Georgia | Aboveground Live trees Belowground roots of live trees | Soil carbon Wood in products |
| RGGI | Aboveground live tree biomass Belowground tree root biomass Soil carbon Coasrse woody debris | Aboveground live non-tree biomass Forest Floor |
| CCX | Aboveground live tree biomass | No other pools accepted |
| IPCC LULUC | None-this protocol just has suggested guidelines | Aboveground Live trees Down dead wood Stumps and dead roots Forest Floor Soil carbon wood in products |
