Page 7 - Climate Change Impacts in the United States

7: FORESTS

In the U.S., afforestation (active establishment or planting of the amount of carbon stored in existing forests if fires occur
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forests) has the potential to capture and store a maximum of more frequently.
225 million tons of additional carbon per year from 2010 to
2110 39,48 (an amount almost equivalent to the current annual Carbon management on existing forests can include practices
carbon storage in forests). Tree and shrub encroachment into that increase forest growth, such as fertilization, irrigation,
grasslands, rangelands, and savannas provides a large potential switching to fast-growing planting stock, shorter rotations,
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carbon sink that could exceed half of what existing U.S. forests and weed, disease, and insect control. In addition, forest
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capture and store annually. management can increase average forest carbon stocks by
increasing the interval between harvests, by decreasing harvest
Expansion of urban and suburban areas is responsible for much intensity, or by focused density/species management. 4,51 Since
of the current and expected loss of U.S. forestland, although 1990, CO 2 emissions from wildland forest fires in the lower 48
these human-dominated areas often have extensive tree cover United States have averaged about 67 million tons of carbon
and potential carbon storage (see also Ch. 13: Land Use & Land per year. 52,53 While forest management practices can reduce
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Cover Change). In addition, the increasing prevalence of on-site carbon stocks, they may also help reduce future
extreme conditions that encourage wildfires can convert some climate change by providing feedstock material for bioenergy
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forests to shrublands and meadows or permanently reduce production and by possibly avoiding future, potentially larger,
wildfire emissions through fuel treatments (Figure 7.2). 1

Forests and Carbon
Figure 7.6. Historical, current,
and projected annual rates of
forest ecosystem and harvested
wood product CO2 net emissions/
sequestration in the U.S. from
1635 to 2055. In the top panel,
the change in the historical annual
carbon emissions (black line) in
the early 1900s corresponds to the
peak in the transformation of large
parts of the U.S. from forested land
to agricultural land uses. Green
shading shows this decline in forest
land area. In the bottom panel,
future projections shown under
higher (A2) and lower (B2 and
A1B) emissions scenarios show
forests as carbon sources (due to
loss of forest area and accelerating
disturbance rates) rather than sinks
in the latter half of this century.
The A1B scenario assumes similar
emissions to the A2 scenario used
in this report through 2050, and a
slow decline thereafter. (Data from
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Birdsey 2006; USFS 2012; EPA
53
2013. )

181 CLIMATE CHANGE IMPACTS IN THE UNITED STATES