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Carbon Components

by mhowell last modified 2007-03-08 18:36

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.  Summation equation


Carbon tree figure

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 

CategoryCarbon Pool 

Overstory trees

Understory trees and shrubs

Groundcover: Herbaceous, grass, woody

 Belowground biomass

Forest Floor

Mineral soil organic C


 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

EntityRequired poolOptional 
DOE 1605bNone-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



Soil carbon

wood in products


Aboveground tree biomass

Standing dead biomass

Lying deadwood

Herbaceous understory and shrubs


Litter and duff 


Aboveground Live trees

Belowground roots of live trees 

 Soil carbon

Wood in products


Aboveground live tree biomass 

Belowground tree root biomass

Soil carbon

Coasrse woody debris

Aboveground live non-tree biomass

Forest Floor

 CCXAboveground live tree biomassNo other pools accepted
IPCC LULUCNone-this protocol just has suggested guidelines

Aboveground Live trees 

Down dead wood

Stumps and dead roots

Forest Floor

Soil carbon

wood in products