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Carbon Estimation

by mhowell last modified 2007-03-08 17:56

Inventory or look-up tables?

            As individual trees and stands of trees grow they sequester carbon within their main stem wood and bark as well as within branches and foliage.  Sequestration of carbon in main stem wood results in longer term sequestration since main stem wood remains in place for long periods of time (decades).  Tree and stand growth rates, and hence carbon sequestration rates, vary by many factors such as: stand type, stand age, site productivity/quality, stand density, as well as silvicultural inputs/treatments.  A great deal of scientific investigation into the inventory of and development patterns for tree has been carried out over the past 50 plus years.  Two important results of this effort has been the creation of sampling protocols to determine current standing timber inventories and simulation models to project how these inventories will develop over time.

     Landowners with timber interests may well have timber inventories (and potentially growth and yield models) that can readily be utilized to estimate carbon contents in standing trees.  Other landowners may have only very limited information about their forest such as the forest type and approximate stand age.  Registries differ in the expected amount of sampling that landowners may be required to complete ranging from annual inventories to virtually no inventory.  In the case of no inventory, tables with average expected rates of growth for forest types in a region are utilized to approximate growth (See the carbon calculator). 

    On the ground inventories are clearly more expensive than the use of look-up tables but reduce uncertainties in the estimates.  In the language of forest inventory, a sampling intensity that results in a demonstrated sample precision of 15% allowable error or less for total tons green weight may be required.  This might typically require 1 plot every 1 to 4 acres.  These green ton estimates then are multiplied by some correction factors for specific gravity to estimate dry tons and then dry tons are multiplied by 0.5 to get tons of C.

  Example Look-up table.

Forest

AGE

Pulp wood

C

Saw Timber C

  Yr

--tons-C/acre---
10
0.16
0
15
2.42
0
20
5.67
0
25
8.66
0.35
30
10.6
1.38
35
11.66
2.78
40
11.75
4.63
45
11.22
6.63
50
10.44
8.48
55
9.6
10.07

General Process to Register Forest Projects

   Registration of a forest carbon offset typically requires the following steps:

1) Identify boundaries of land parcel on the ground (i.e., tax plat, aerial photo)

2) Identify eligibility of project.  For example, does it meet additionality constraints if needed or is a conservation easement present.

3) Estimate C offset potential in metric tons of CO2 per acre.  This may require an on the ground inventory, or look tables may suffice.

4) Register potential C offset credits according to registry guidelines in your region.

5) Report annual updates on the condition of the C offset.  For example, is the stand growing well or has fire recently entered the stand.