Indicator 27.
Contribution of Forest Ecosystems to the Total Global Carbon Budget, Including Absorption
and Release of Carbon (Standing Biomass, Coarse Woody Debris, Peat, and Soil Carbon)
Average net C pool change per year
(Mt/yr)
Average net C pool change per yr
(Mt/yr)
250.0
Above-ground live
200.0
Above-ground
standing dead
150.0
Understory
Down dead
100.0
Forest floor
50.0
Below-ground live
0.0
1953
-1962
1963
-1976
1977
-1986
1987
-1996
Below-ground dead
100
75
50
25
0
-25
19531962
19631976
19771986
19871996
Year
North
Years of Period
South
Rocky Mtn
Pacific Coast
Figure 27-1. Average annual net forest carbon change
(Mt/yr), 1953–1996.
Figure 27-2. Average annual net forest carbon change
(Mt/yr) by region.
What Is the Indicator and Why Is It Important?
What Does the Indicator Show?
Because plants utilize carbon dioxide in the
photosynthesis process, forests provide a primary
vehicle for sequestering carbon from the atmosphere,
During this process, the carbon becomes part of the
plant mass. Thus, managing forests to sequester
carbon reduces the net amount of carbon dioxide
accumulating in the atmosphere. Less carbon dioxide
in the atmosphere may help reduce the possibility of
human-induced climate change. The United States
emitted a gross 1,909 megatonnes (Mt) equivalent of C
in the year 2000. This indicator provides an estimate
of forest carbon sequestration that may be subtracted
from the gross emissions to estimate net emissions.
Currently, soil carbon changes are not included in
this indicator; however, forest soils are expected to be
sequestering carbon.
A positive number means carbon is being sequestered
from the atmosphere into the forest. The average
annual net change in nonsoil forest ecosystem carbon
pools for the period 1953–1997 is 175 Mt C/yr being
absorbed by forests from the atmosphere. Between
1987 and 1996, about 135 MtC/yr were added to
nonsoil forest carbon stocks. Forest ecosystems
sequester about 10 percent of the gross U.S. greenhouse
gas emissions, with additional carbon sequestration
accounted for in products (see indicator 28). U.S. forest
ecosystems sequester more than 10 percent of the
global total for terrestrial ecosystems. The decrease
in sequestration in the last period is thought to be
because of more accurate data, increased harvests
relative to growth, and accounting issues related to
emissions from dead wood. The North Region is
sequestering the greatest amount of carbon, followed
by the Rocky Mountain Region. The trend of decreasing
sequestration in the South Region is because of the
increase in harvesting relative to growth. This harvested
carbon will be shown as being sequestered in wood
products (see indicator 28).
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