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Page 814
Appendix P
Reforestation
The most comprehensive analysis of the potential for
sequestering carbon in trees in the United States is that
undertaken by Moulton and Richards (1990) of the U.S. Forest
Service. This is a detailed analysis of the land available in the
United States that could support trees, the carbon uptake that
might be expected, and actual costs for each type of land to be
managed. The analysis assumes that trees could be planted on
economically marginal and environmentally sensitive pasture and
croplands and that forest management programs could increase carbon
uptake on many nonfederal forestlands. After analyzing the
potential carbon uptake and cost per ton for 70 region and
land-type classes, Moulton and Richards arrange these in order by
cost per ton and assemble a supply curve for carbon sequestering.
The analysis concludes that up to 56.4 percent of U.S. emissions
could be sequestered in domestic trees at costs ranging from $5.80
to $47.75/t of carbon (C) (there is no adjustment for the small
energy and CO2 cost of implementing
such a program).1
The analysis has a 40-year time horizon and so does not confront
the consequences of declining growth rates as trees approach
maturity or of the long-term possibilities for tree maintenance or
harvest. Two sets of numbers that heavily influence the numeric
results but are likely to elicit some discussion are land rental
rates and the ratio between carbon uptake in marketable timber and
total ecosystem carbon uptake. Both sets of numbers are carefully
laid out in the analysis and could be manipulated by an analyst
with different notions. The ecosystem carbon ratios, for example,
ranges from 1.8 to 8.4 and include considerable carbon accumulation
in soils. The result of using high ecosystem carbon ratios is that
average carbon accumulation for the full program amounts to 5.3
t/hectare(ha)/yr. Trexler (1990) suggests that values nearer 3.7
might be more within expectation for a
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Representative terms from entire chapter:
forest management
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program of this magnitude. Any comparison with current forest
growth rates must acknowledge that most of the increased growth
envisioned in the Moulton and Richards analysis would be on what is
characterized as ''marginal cropland" but which would in fact be
very good forestland. The analysis does not include a start-up
period for tree planting and establishment but assumes "instant
trees" with all establishment costs in the first year.
The structure of the Moulton and Richards report is such that
one can examine the program incrementally. Table P.1 shows the
implications of planting enough trees—in order of increasing
dollars per ton of carbon—to sequester carbon at rates of 10
percent, 20 percent, and 56.4 percent of current U.S. total CO2 emissions. The table shows that at the
10 percent level most of the uptake would be accomplished by
changing forest management practices on current forestlands and
planting on marginal pasturelands, but that in order to get very
much of the maximum potential, large-scale inclusion of marginal
croplands would be required.
Recognizing that the Moulton and Richards analysis suggests that
56.4 percent of U.S. CO2 emissions
could perhaps be offset with a massive commitment to a
reforestation program, the Mitigation Panel adopts a very
conservative approach to estimating the carbon offset that might be
envisioned. This analysis accepts that the 10 percent objective
described by Moulton and Richards is a reasonable initial target
and that reforestation of economically marginal or environmentally
sensitive pasture and croplands and nonfederal forestlands to a
total 28.7 Mha could take place at costs as described in their
analysis. The carbon sequestering rate is then divided by 2 to
ensure that only carbon that is truly taken into long-term storage
is counted. This baseline then suggests that 240 Mt CO2 could be sequestered at costs between $3
and $10/t CO2 (average cost is
$7.20/t CO2). Demonstration projects
could verify the lower costs and higher targets for total
sequestration projected by some.
TABLE P.1 Reforestation Program Costs by Percentage
Reduction
Annual CO2 Offset
(%/M short tons)
Land Requirement (M acres)
Total Annual Cost (Billion $)
Average Cost ($/t carbon)
5/72
36.9
0.7
9.72
10/143
70.9
1.7
12.02
20/286
138.4
4.5
15.73
30/429
197.6
7.7
17.91
SOURCE: Moulton and Richards (1990).
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Note
1. Tons (t) are metric; 1 Mt = 1 megaton = 1 million tons.
References
Moulton, R. J., and K. R. Richards. 1990. Costs of sequestering
carbon through tree planting and forest management in the United
States. U.S. Forest Service Report. Draft. U.S. Department of
Agriculture, Washington, D.C.
Trexler, M. C. 1990. Minding the carbon store: Weighing U.S.
forest strategies to slow global warming. Draft. World Resources
Institute, Washington, D.C.
