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Criterion 5 Indicator 26

Total Forest Ecosystem Biomass and Carbon Pool, and If Appropriate, by Forest Type, Age Class, and Successional Stage   Human activities have changed and are continuing to change the chemical composition of the atmosphere. Many of these influences, such as fossil fuel burning, land management activities, and the widespread use of chemical compounds, release greenhouse gases, which increase the amount of radiation absorbed by the atmosphere. The changes caused by these gases may alter the Earth’s climate.
Carbon dioxide is one a major greenhouse gas. Forests naturally take in and store carbon as plants grow, providing a large carbon "sink". Thus, information regarding the forest carbon content provides important information for regulating atmospheric carbon. Knowledge of biomass provides similar information as biomass is approximately 50% carbon. Biomass is also a renewable energy source. For more information on carbon as a policy issue, see Heath and Joyce (1997).

Can This Indicator Be Quantified
Aboveground biomass can be summarized from data in the Westwide Forest Inventory Data Base (Woudenberg and Farrenkopf, 1995). Biomass includes biomass of live and dead trees greater than 2.5 cm dbh. Biomass estimates (dry weight) are provided in the database, calculated by applying biomass equations to measured or estimated diameters and heights. Biomass is approximately 50% carbon, so the carbon pool of biomass can be estimated by multiplying biomass in terms of dry weight by 50%. Estimates of carbon in woody debris, forest floor, and soil can be estimated using average carbon factors contained in Birdsey (1992), multiplied by plot information from the inventory data. The forest types reported in this data were adapted to correspond with forest types used by the Oregon Department of Forestry. Table 26-1 presents biomass of only the aboveground live and dead trees by forest type. The area of forest corresponding with these estimates is also presented. The entire carbon pool of all forest components (including below ground tree carbon, forest floor, soil, understory vegetation) by forest type and age class is presented in Table 26-2.
Table 26-1. Aboveground live and dead tree biomass (dry weight) by forest type.
Forest-typeBiomass (million metric tons dry wt.)Area (thousands of hectares)
Ponderosa Pine & other pines59.51,973.40
Spruce; Hemlock17.4166.9
True Fir; Mt. Hemlock94.81,175.60
Lodgepole pine20.9779
Mixed conifer; mixed deciduous168.31,875.30
Regenerating Forest/Chaparral0.866
All inventoried forest land74310,356.90

Table 26-2. Carbon (million metric tons) in forest ecosystems by forest type and age-class.
Forest TypeAge-Class
Ponderosa Pine16.91831.7122.392.234.214.1329.4
Spruce; Hemlock0.
True Fir1.18.510.558.384.945.223231.4
Lodgepole pine5.116.612.931.824.27.62.2100.2
Mixed conifer; Mixed deciduous4.353.978.468.250.935.341.4332.2
Regenerating Forest/Chaparral6.90000006.9


Data Source and Availability
  • Westwide Forest Inventory Data Base (Woudenberg and Farrenkopf, 1995).
This database contains plot and tree records of an inventory of sample plots throughout the western United States. The sample is designed to produce estimates of total volume of a State on productive forestland within a designated sampling error. The summary statistics in this indicator are based on a pre-release of the data (Woudenberg and Farrenkopf, 1995). Tree measurements are not taken on reserved forestland or on forestland of low productivity. Tree data were not collected on approximately 1,585,662 hectares of forestland.

Reliability of Data
At the time of the inventory, the data provided total volume for productive forestlands in the state with a sampling error of " 3%. The error would be similar in terms of biomass. The data on privately-owned lands in western Oregon were collected in 1985, and are somewhat dated. New inventory data are scheduled for release soon. The tree data for private lands in eastern Oregon were collected in 1992, however, plot data were not necessarily updated. The data for National Forest and Bureau of Land Management forests were collected in 1995. As new data for privately-owned lands are released and analyzed, the results will become increasingly reliable, especially for aboveground carbon. Estimates of carbon in other components of the forest ecosystem are generally accurate within about "15% at ? = 0.10.

One inventory plot represents on average 1,312 hectares. Area estimates are augmented to match land areas from the 1980 census. The minimum area for classification of forest land is 0.4048 hectares.

Recommended Action for Data Collection
For a comprehensive carbon estimate, inventory data need to be collected on all forestlands. Currently, data are not collected on about 10% of the forestland base. A consistent compilation of the inventory data would also help provide estimates of this indicator.

Forestland – Land at least 10% stocked by forest trees of any size, including land that formerly had such tree cover and that will be regenerated. Strips of forest must have a crown width of 36.58 meters to qualify as forestland.
Productive forestland – Forestland that is capable of producing more than 1.4 cubic meters per hectare per year of industrial wood in natural stands.
Reserved forestland Forestland that is withdrawn from harvest by statute or administrative regulation.

Selected References
Birdsey, R.A. 1992. Carbon storage and accumulation in United States forest ecosystems. USDA Forest Service, Washington Office, General Technical Report, WO-59. 51 p.
Heath, L.S., and L.A. Joyce. 1997. Carbon sequestration in forests as a national policy issue. In: Communicating the role of silviculture in managing the national forests: Proceedings of the National Silviculture Workshop, p. 29-36. US DA Forest Service, Northeastern Forest Experiment Station, General Technical Report NE-GTR-238. 205 p.
Woudenberg, S.W., and T.O. Farrenkopf. 1995. The Westwide forest inventory data base: user’s manual. USDA Forest Service, Intermountain Research Station, General Technical Report INT-GTR-317. 67 p.