Criterion 5. Maintenance of Forest Contribution to Global Carbon Cycles
National Report on Sustainable Forests—2010
Indicator 5.22.
Total Forest Ecosystem Carbon Pools and Fluxes
What is the indicator and why is it important?
What does the indicator show?
The United States emitted a gross 6.0 billion metric tons of
CO2 in the year 2006. Because plants use carbon dioxide in the
photosynthesis process, forests provide a primary vehicle to
sequester carbon from the atmosphere. During this process, the
carbon becomes part of the plant mass. Once forest biomass
dies, carbon remains in the forest ecosystem and cycles through
standing dead trees, downed dead wood, duff and litter, and
finally soil carbon pools. Thus, managing forest ecosystems
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 and extent of
human-induced climate change. In contrast, forests can also
serve as a net emitter of CO2 during years of extreme wildfires
or widespread disturbance. In addition to showing current
estimates of carbon pools, this indicator provides estimates
of annual forest carbon storage changes (fluxes) that may be
subtracted from the gross emissions to estimate net emissions.
All carbon pools, with the exception of soil carbon, are
estimated using the Forest Service’s Forest Inventory and
Analysis (FIA) measured data or imputed data, along with
inventory-to-carbon relationships, developed using information from ecological studies. Thus, trends of volume and area
in other indicators based on FIA data should be consistent
with this information. Forest ecosystem carbon stocks in the
United States continue to represent a substantial carbon pool
of more than 156,000 Tg CO2e (fig. 22-1), with live trees and
organic soil carbon levels accounting for most of this stock.
The forest carbon stock is equivalent to more than 25 years of
CO2 emissions in the United States. The live tree carbon stock
is concentrated on the West coast, Rocky Mountains, Appalachian Mountains, and in other areas of the Eastern United
States (fig. 22-2).
Figure 22-1. Total carbon stocks by forest ecosystem
component in the United States, 1990–2007 (Tg CO2e).
Figure 22-2. Forest aboveground live biomass carbon
stocks by county for United States, 2006 (Mg CO2e).
Tg CO2 e (thousands)
70
60
50
40
30
20
10
19
9
19 0
9
19 1
9
19 2
9
19 3
9
19 4
9
19 5
9
19 6
9
19 7
9
19 8
9
20 9
0
20 0
0
20 1
0
20 2
0
20 3
0
20 4
0
20 5
0
20 6
07
0
Year
Aboveground biomass
Belowground biomass
Dead wood
Litter
Soil organic carbon
500 miles
Albers Equal-Area Conic Projection
Aboveground live-tree biomass
(Mg CO2e)
Greater than 300
251–300
201–250
150–200
Less than 150
Less than 5% forest land or no data
Last Updated June 2011 1
0.6
0.5
Percent
National Report on Sustainable Forests—2010
0.4
In terms of annual changes or carbon flux, both above- and
below-ground forest ecosystem living biomass components
account for most of annual carbon sequestration (fig. 22-3).
These rates of sequestration have remained rather static since
2000. The spatial distribution of forest sequestration is evenly
distributed within forested regions of the country (fig. 22-4).
U.S. forests offset more than 11 percent of total U.S. CO2
emissions in 2006. This rate of offset has remained relatively
constant for the past two decades (fig. 22-5). Overall, the
0.3
tremendous
forest carbon stocks of the United States continue
0.2
to gradually
increase, increasing GHG emissions continue to
greatly
outpace
what forests can sequester annually.
0.1
Figure 22-3. Percent of total carbon stock by forest
ecosystem component sequestered annually in the
United States, 1990–2006.
Figure 22-5. Total greenhouse gas emissions versus total forest ecosystem sequestration in the United States,
1990–2006 (Tg CO2e).
0
What has changed since 2003?
– 0.1
0.8
9
19 2
93
19
94
19
95
19
96
19
97
19
9
19 8
99
20
00
20
01
20
0
20 2
03
20
0
20 4
05
20
06
91
19
7
0.7
Tg CO2e (thousands)
6
0.6
0.5
0.4
0.3
0.2
5
4
3
2
1
06
05
20
04
20
03
20
02
20
01
20
00
20
99
20
98
19
97
19
96
19
95
19
94
19
19
93
19
19
90
19
19
0
92
0
0.1
91
Percent
19
19
90
Total forest ecosystem carbon stocks were maintained with
positive increases from forest area
expansion and growth.
Year
Aboveground
biomass
Litter
Despite these increases,
total
U.S. GHG emissions
still
Belowground biomass
Soil organic carbon
outpaced forest Dead
ecosystem
gains.
wood
Year
– 0.1
9
19 2
93
19
94
19
95
19
96
19
97
19
9
19 8
99
20
00
20
01
20
0
20 2
03
20
0
20 4
05
20
06
91
Total forest sequestion
19
19
19
90
Total GHG emission
Year
Aboveground biomass
Belowground biomass
Dead wood
Litter
Soil organic carbon
Figure 22-4. Total forest ecosystem carbon stock annual flux by county in the United States, 2006 (Mg CO2e per year).
7
Tg CO2e (thousands)
6
5
4
3
2
1
Total forest sequestion
06
20
04
05
Year
Total GHG emission
20
20
02
03
20
01
20
20
99
00
20
19
97
98
19
19
95
96
19
94
19
19
92
93
19
19
19
19
90
91
0
Aboveground stock changes
(Mg CO2e yr – 1)
Greater than 10
2.1 to 10
– 1.9 to 2.0
500 miles
Albers Equal-Area Conic Projection
– 10 to – 2
Less than – 10
Less than 5% forest land or no data
Note: In conformance with IPCC reporting protocols, carbon sequuestration is denoted by negative numbers (blue) while carbon emissions to the atmosphere are
represented by positive numbers (red).
Last Updated June 2011 2