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We examined the carbon dynamics of the southeastern United States over the past two centuries in order to estimate the presettlement carbon pool, document carbon losses from deforestation, and determine whether this region is a source or a sink of atmospheric CO2

Carbon Budget Of The Southeastern United-States Biota - Analysis Of Historical Change In Trend From Source To Sink

SCIENCE, no. 4467 (1980): 321-323

Cited: 47|Views14
WOS SCIENCE

Abstract

Documentation of settlement patterns and deforestation in the southeastern United States allows evaluation of regional carbon dynamics since A.D. 1750. From 1750 to 1950, the Southeast was a net source for carbon at an average rate of 0.13 gigaton per year. Only in the past 20 to 30 years has increased productivity of commercial forests r...More

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Introduction
  • The observed increase in atmospheric CO2 over preindustrial levels has been ascribed largely to burning of fossil fuels [1] and to forest clearing and burning [2].
  • From 1750 to 1950, the Southeast was a net source for carbon at an average rate of0.13 gigaton per year.
  • In the past 20 to 30 years has increased productivity of commercial forests resulted in a sink for atmospheric carbon dioxide of 0.07 gigaton per year.
Highlights
  • The observed increase in atmospheric CO2 over preindustrial levels has been ascribed largely to burning of fossil fuels [1] and to forest clearing and burning [2]
  • In the past 20 to 30 years has increased productivity of commercial forests resulted in a sink for atmospheric carbon dioxide of 0.07 gigaton per year
  • We examined the carbon dynamics of the southeastern United States over the past two centuries in order to estimate the presettlement carbon pool, document carbon losses from deforestation, and determine whether this region is a source or a sink of atmospheric CO2
  • The aboveground biomass of the virgin forests averaged 343 Mg/ha, total live biomass was estimated as 460 Mg/ha, and total carbon averaged 327 Mg/ha [12]
  • Replacement of nearly 55 percent of the original forest land with secondary forests did not restore carbon reserves depleted by extensive agricultural utilization over that 210-year period
  • *Assuming that the land area of virgin and secondary forests and nonforest land is the same as in 1977 and that productivity of commercial forests increases at the same rate as in 1970 to 1977 (1.78 Mg of live biomass per hectare per year). tAssuming that the land area of virgin forest is the same as in 1977, that the area of secondary forest decreases by 10 percent as cultivated and urban land increases, and that productivity of commercial forests remains at 1977 levels
Results
  • The authors examined the carbon dynamics of the southeastern United States over the past two centuries in order to estimate the presettlement carbon pool, document carbon losses from deforestation, and determine whether this region is a source or a sink of atmospheric CO2.
  • Before settlement (A.D. 1750) (Fig. 1), 91.6 percent of the land area of these states was forest, 3.8 percent was prairie, and 4.6 percent was marsh [6].
  • Estimates of timber volume for virgin forests of 1880 [8] and for secondary forests of 1952, 1962, 1970, and 1977 [5] were used to estimate total live biomass and total carbon on forested land [12].
  • Land clearing and cultivation were estimated to diminish soil carbon by 40 percent [16, 17].
  • Replacement of nearly 55 percent of the original forest land with secondary forests did not restore carbon reserves depleted by extensive agricultural utilization over that 210-year period.
  • Between 1952 and 1977, the aboveground biomass on commercial forest land increased from 53.2 to 72.2 Mg/ha [5].
  • This gain reflects the increase in holdings of intensively managed forest land (Fig. 1), on which net annual growth has increased due to reforestation of nonstocked areas and control of species composition and stand density [10].
  • *Assuming that the land area of virgin and secondary forests and nonforest land is the same as in 1977 and that productivity of commercial forests increases at the same rate as in 1970 to 1977 (1.78 Mg of live biomass per hectare per year).
  • TAssuming that the land area of virgin forest is the same as in 1977, that the area of secondary forest decreases by 10 percent as cultivated and urban land increases, and that productivity of commercial forests remains at 1977 levels.
Conclusion
  • Under the assumptions given in Table 1, a 10 percent decrease in the area of commercial forests changes the Southeast from a carbon sink to a small source.
  • With sustained high productivity, stabilization or increase in commercial forest area, and greater net growth can the terrestrial system of the Southeast continue to gain carbon.
  • Environmental Sciences Division, Oak Ridge National Laboratory
Tables
  • Table1: Carbon in gigatons for virgin forest, secondary forest, and nonforest land of the southeastern United States, A.D. 1750 to 1977, with projections to 2030
Download tables as Excel
Funding
  • This research was supported by the National Science Foundation's Ecosystem Studies Program under interagency agreement DEB 77-26722 with the U.S Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation
Reference
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  • 19. For the Southeast in 1976, total wood storage products = 3.42 x 109 ft3 = 0.025 Gton of stored carbon (5). At this rate, the total carbon gain would be increased 20 percent by A.D. 2030 but total carbon would amount to only 6.38 Gton for the comfbined biomass and wood products.
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  • 0036-8075/80/1017-0323$00.50/0 Copyright K 1980 AAAS
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