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HOW MUCH CARBON HAVE YOUR TREES STORED?

The Alabama Forestry Commission is developing guidelines to help forest landowners and Foresters measure carbon dioxide that is produced and stored in Alabama’s forests. (These guidelines will be available on this website as soon as a the review process is completed and the guidelines are finalized.)

The most accurate way to estimate stored carbon and subsequently CO2 equivalents is to directly measure the trees on a specific site. This involves developing and implementing a sampling inventory or timber cruise. This method is the most costly but also the most accurate. In most situations, forest landowners should utilize a Registered Forester to conduct these measurements. (For a listing of Registered Foresters providing services in your area, visit the Alabama Forestry Commission’s website.) Most forest inventories measure live trees as cords, board feet, or tons. Because carbon dioxide is traded in tons, and biomass tons can be obtained from a tree inventory, tons will be used as the base unit in calculating carbon accumulations (and subsequently CO2 equivalents).

In summary, the following steps may be taken to estimate CO2 stored in living, growing trees based on an estimate of merchantable wood in the tree:

USE THE FOLLOWING SIX STEP PROCESS TO DETERMINE ENTIRE LIVE TREE, ABOVE-GROUND CARBON DIOXIDE (CO2) EQUIVALENT:

STEP 1: INVENTORY MERCHANTABLE ROUNDWOOD.
Using traditional forest inventory procedures estimate the green tons of merchantable roundwood biomass (i.e. pulpwood, sawtimber, etc.) in the main tree’s bole or stem. If the inventory includes bark, multiply green tons of wood and bark by 0.9 to obtain an estimate of green tons of wood only for each product.

If inventory volumes are reported in units other than tons, to convert to tons use either local conversion factors or the following general conversion factors:

  Pine Sawtimber and CNS:
Pine Pulpwood:
Hardwood Sawtimber:
Hardwood Pulpwood:
From cubic feet to cords:
7.50 tons per MBF, Scribner
2.68 tons per cord
8.75 tons per MBF, Doyle
2.90 tons per cord
90 cubic feet (ft3) per cord (solid wood & bark)
STEP 2: ESTIMATE TOTAL TREE BIOMASS.
There is considerably less biomass in the merchantable roundwood (i.e. pulpwood, sawtimber, etc.) than in the entire tree. However, carbon is stored in the entire tree including the limbs and tree tops and should be included. To estimate entire tree biomass from merchantable roundwood biomass, multiply the inventory weights calculated in STEP 1 by the following conversion factor for the general species group listed below. This will provide an estimate of the green weight of the entire tree.
Merchantable to Total Tree Conversion Factors:
Softwood Hardwood Average
1.12 1.33 1.19
STEP 3: CONVERT FROM GREEN TONS TO DRY TONS.
Multiply green tons of the entire tree obtained in STEP 2 by the specific gravity conversion factor for the general species groups listed below. This will provide an estimate of the dry weight of the entire tree.
Specific Gravity Conversion Factors:
Softwood Hardwood Average
0.463 0.529 0.500
STEP 4: CONVERT TREE BIOMASS TO CARBON EQUIVALENT.
Multiply the dry tons of the entire tree obtained in STEP 3 by 0.5 to obtain a comparable weight of entire tree’s sequestered carbon.

STEP 5: CONVERT CARBON TO CARBON DIOXIDE EQUIVALENT.
Multiple the tons of sequestered carbon obtained in STEP 4 by 3.67 to obtain a comparable weight of carbon dioxide equivalent (CO2).

STEP 6: CONVERT SHORT TONS TO METRIC TONNES.
Typical southern forest inventories are reported in English or short tons, which equals 2,000 pounds. Most Carbon Dioxide is traded based on metric tonnes, which equals 2,204 pounds. To convert to metric tonnes multiply the short tons by 0.9072.

A generalized formula to estimate metric tonnes carbon dioxide equivalent (MTCO2e) using traditional timber inventory roundwood estimates (reported in short tons) is as follows:
MTCO2e = (Merchantable Weight) x (Total Tree Factor) x (Specific Gravity Factor) x 0.50 x 3.67 x 0.9072

 

EXAMPLE: DIRECT MEASUREMENT OF CO2 STORAGE OF TREES
A landowner hired a registered forester to estimate the merchantable volume of a natural stand of mixed pine-hardwood covering 85 acres in northeast Alabama. The registered forester estimated a total of 765 cords of pine pulpwood, 272 MBF (Scribner) of pine sawtimber, 425 cords of hardwood pulpwood, and 119 MBF of hardwood sawtimber (Doyle).
Step 1:
Convert merchantable estimates to short ton equivalents by general species group:
PPW (765 x 2.68) + PST (272 x 7.50) = 4,090 short tons of softwood on 85 acres
HPW (425 x 2.90) + HST (119 x 8.75) = 2,274 short tons of hardwood on 85 acres
Step 2:
Estimate total tree biomass (green tons):
4,090 x 1.12 = 4,581 short tons tree biomass, softwood
2,274 x 1.33 = 3,024 short tons tree biomass, hardwood
Step 3: Convert to dry tons using specific gravity ratios:
4,581 x 0.463 = 2,121 short tons tree biomass, softwood, DRY
3,024 x 0.529 = 1,600 short tons tree biomass, hardwood, DRY
Step 4: Convert to carbon tons equivalent:
(2,121 + 1,600) x 0.5 = 1,861 short tons carbon equivalent
Step 5: Convert to CO2 tons equivalent:
1,861 x 3.67 = 6,830 short tons carbon dioxide (CO2) equivalent
Step 6: Convert to CO2 metric tonnes equivalent:
6,830 x 0.9072 = 6,196 metric tonnes carbon dioxide equivalent (MTCO2e)

 

1 The conversion rates/multipliers used in the following steps are identified in the Department of Energy’s (DOE) Energy Policy Act, Section 1605(B), Voluntary Reporting Guidelines of Greenhouse Gases, Forestry Appendix, except as otherwise identified.

2 Average wood specific gravity is the density of wood divided by the density of water based on wood dry mass associated with green tree volume.

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Additional Resources:


- Carbon Sequestration
- Carbon Sequestration Publications
- Carbon Sequestration Websites
- Carbon Sequestration FAQs

The Alabama Forestry Commission is currently updating information on the Carbon Sequestration Webpage as new developments occur. Please periodically check this website for new updates.

For more information contact:
Alabama Forestry Commission