Criteria: Forest Carbon
Data Source: USDA Forest Service
Last Updated: March 2019
WHY FOREST CARBON?
Forests perform a number of ecosystem services, including the critical job of sequestering atmospheric carbon dioxide (i.e. CO2, carbon). Climate change is primarily the result of increased concentrations of heat-trapping greenhouse gases, such as C02, in the earth’s atmosphere. Forests ecosystems pull carbon dioxide out of the atmosphere and as they grow, and store that carbon within their soil and plant tissue (i.e. biomass – tree stems, bark, and branches).
In forest ecosystems globally, 31% of carbon is stored in biomass and 69% is stored within the soil.1 If the amount of carbon released into the atmosphere (via respiration, death, decomposition, burning, etc.) is less than the amount sequestered (i.e. stored), the forest is acting as a carbon sink. If the amount of carbon released into the atmosphere is more than the amount sequestered (i.e. stored), the forest is acting as a source of carbon emissions.
In the United States, forest ecosystems sequester enough carbon to offset 11 – 12% of US emissions each year.2, 3 However, a forest’s ability to sequester carbon can be influenced by a variety of factors.5 This means that climate change (and related disturbances) could impact forest ecosystems’ ability to sequester carbon into the future.4
This criterion helps our members understand if forests [in the timberlands surrounding the selected mill(s)] are acting as a carbon sink or source.
SUMMARY
This criterion estimates the net change of [above ground] carbon stored in the geography of interest, over a five-year period. Forests in Focus uses FIA wood volume data to provide estimates of carbon stored in above-ground woody biomass, such as tree stems, bark, and branches (i.e. not soil). Many people view changes in biomass, as represented by the ‘carbon flux’ (the movement of carbon between Earth’s carbon pools), as an important measure of sustainability in itself. Since forests are significant sinks for atmospheric carbon dioxide, scientists and sustainability professionals are interested in understanding how much and for how long carbon stays within that forest [carbon pool]. Because of the close relationship of forest carbon and biomass, growth and drain ratios do ‘double duty’, providing an estimate of the net change of forest carbon volume while also indicating if the amount of biomass (trees) removed from forests is being regrown.
The following equation may be helpful in visualizing this concept:
RISK THRESHOLDS
| LOWER RISK | MEDIUM RISK | HIGHER RISK | |
| Forest Carbon | Less than or equal to 1% net loss of above-ground wood volume annually, or a 5% net loss over a five-year period. | Between 1% to 2% net loss of above-ground wood volume annually, or a 5% to 10% net loss over a five-year period. | More than 2% net loss of above-ground wood volume annually, or a 10% net loss over a five-year period. |
TECHNICAL INFORMATION
The deforestation criterion uses the USDA Forest Service’s Forest Inventory and Analysis (FIA) data. This census of forests in the US is an ongoing effort that reports on status and trends in forest area and location; in the species, size, and health of trees; in total tree growth, mortality, and removals by harvest; in wood production and utilization rates by various products; and in forest land ownership. Forests in Focus uses the FIA designation of timberland to standardize how we define forests across the USA. Timberland is forest land that is at least one acre, not legally withdrawn from timber production, and that is capable of producing more than 20 cubic feet per acre per year of [industrial] wood.
POSSIBLE DATA AND ANALYSIS LIMITATIONS
As a result of differences in the methodology used to scale data (from plot to Hexagon or from plots to Assessment Area), percent and net change results may differ slightly between the Assessment Area Dashboard and Summary Dashboard.
The FIA methodology Forests in Focus utilizes is designed to support an understanding of the nation’s forest resource and to support observations about trends at different scales. As with any analysis, there are statistical limitations to results, especially at finer scales. FIA data plots, for example, may not be evenly distributed across a landscape, affecting statistical reliability due to a small sample size. Furthermore, several states including Wyoming, New Mexico and Nevada were not included in the Forests in Focus assessment, as the FIA data was insufficient to provide calculations consistent with the other states.
1, 4 Food and Agriculture Organization. Forests and climate change.
2 Ecosphere. Carbon stocks and stock change on federal forest lands of the United States.
3 Congressional Research Service (CRS). U.S. Forest Carbon Data: In Brief.
5 BioScience. Climate Change and Forest Disturbances.