Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 83

Applying these calculations to data developed by the USDA Forest Service for the
Inventory of U.S. Greenhouse Gas Emissions and Sinks yields a result of 150 metric
tons of carbon per hectare (or 61 metric tons of carbon per acre) * for the carbon stock
density of U.S forests in 2010, with an annual net change in carbon stock per area in
2010 of 0.82 metric tons of carbon sequestered per hectare per year (or 0.33 metric
tons of carbon sequestered per acre per year). These values include carbon in the five
forest pools of above-ground biomass, below-ground biomass, deadwood, litter, and
soil organic carbon, and they are based on state-level Forest Inventory and Analysis
(FIA) data. Forest carbon stocks and carbon stock change are based on the stock dif-
ference methodology and algorithms described by Smith et al. (2010).
Conversion Factors for Carbon Sequestered Annually
by One Acre of Average U.S. Forest
Due to rounding, performing the calculations given in the equations below may not
return the exact results shown. In the following calculation, negative values indicate
carbon sequestration.
(-0.33 metric ton C per acre/year) × (44 units CO 2 ÷ 12 units C) = -1.22 metric ton
CO 2 sequestered annually by one acre of average U.S. forest.
Note that this is an estimate for “average” U.S. forests in 2010 (i.e., for U.S. forests as
a whole in 2010). Significant geographical variations underlie the national estimates,
and the values calculated here might not be representative of individual regions of
states. To estimate carbon sequestered for additional acres in one year, simply mul-
tiply the number of acres by 1.22 metric tons CO 2 per acre/year. From 2000 to 2010,
the average annual sequestration per area was 0.73 metric tons C per hectare/year
(or 0.30 metric tons C per acre/year) in the United States, with a minimum value of
0.36 metric tons C per hectare/year (or 0.15 metric tons C per acre/year) in 2000, and
a maximum value of 0.83 metric tons C per hectare/year (or 0.34 metric tons C per
acre/year) in 2006.
Acres of U.S. Forest Preserved from Conversion to Cropland
The carbon stock density of U.S. forests in 2010 was 150 metric tons of carbon per
hectare (or 61 metric tons of carbon per acre) (USEPA, 2012b). This estimate is
composed of the five carbon pools of above-ground biomass (52 metric tons C per
hectare), below-ground biomass (10 metric tons C per hectare), dead wood (9 metric
tons C per hectare), litter (17 metric tons per C hectare), and soil organic carbons (62
metric tons C per hectare).
The Inventory of U.S. Greenhouse Gas Emissions and Sinks estimates soil car-
bon stock changes using U.S.-specific equations and data from the USDA Natural
Resource Inventory and the CENTURY biogeochemical model (USEPA, 2012b).
When calculating carbon stock changes in biomass due to conversion from for-
estland to cropland, the IPCC guidelines indicate that the average carbon stock
change is equal to the carbon stock change due to removal of biomass from the
* 1 hectare = 10,000 m 2 ; 100 m by 100 m; 2.47 acres.