HUMAN APPROPRIATION OF THE PRODUCTS OF PHOTOSYNTHESIS

Earths resources are consumed by one of its 5-30 million species homo sapiens or man at a rate disproportionately greater than any other species. Mans impact on the biosphere is measured in terms of net primary production (NPP). NPP is the amount of energy remaining after the respiration of primary producers (mostly plants) is subtracted from the total amount of biologically fixed energy (mostly solar). Human output is determined by 1) the direct NPP used for food fuel fiber or timber which yields a low estimate 2) all NPP of cropland devoted to human activity and 3) both 1) and 2) and land conversion for cities or pastures as well as conversion which results in desertification and overuse of lands. This last output determination yields a high estimate. Calculations are made for global NPP and each of the 3 estimates of low intermediate and high human output. Data are based on estimates by Ajtay et al. Armentano and Loucks and Houghton et al. and on the Food and Agriculture Organizations (FAO) summaries. Petagram (Pg) is used to calculate organic matter; this is equivalent to 10 to the 15th power grams or 10 to the 9th power metric tons. Carbon has been converted to organic matter by multiplying by 2.2. Matter in kilocalories has been converted to organic matter by dividing by 5. Intermediate or conservative estimates have been included. The standard of biomass is 1244 Pg and an annual NPP to 132.1. The NPP of marine and freshwater ecosystems is considered to be 92.4 Pg which is a low estimate. The low calculation of human (5 billion persons) consumption of plants at a caloric intake of 2500 kilocalories/person/day is .91 Pg of organic matter which equals .76 Pg of vegetable matter. The global production of human food is 1/7 Pg for grains and for human and livestock fed or .85 Pg of dry grain material and .3 Pg in nongrain dry material with dry grain material and .3 Pg in nongrain dry material with a subtraction of 20% for water content. 34% or .39 Pg is lost to waste and spoilage. Consumption by livestock forest usage and aquatic ecosystems is computed. The overall estimate for human use if 7.2 Pg of organic matter/year or 3% of total NPP/year. The intermediate figures take into account cropland pastureland forest use and conversion; the overall estimate of human use is 42.6 Pg of NPP/year of 19.0% (42.6/224.5) of NPP (30.7% on land and 2.2% on seas). The high estimate yields human use of 58.1 Pg/year on land or 40% (58.1/149.6) of potential land productivity or 25% (60.1/149.8 + 92.4) of land and water NPP. The remaining 60% of land is also affected by humans. The figures reflect the current patterns of exploitation distribution and consumption of a much larger population. These patterns amount to using >50% of NPP of land; there must be limits to growth.

[1]  T. Platt,et al.  Autotrophic Picoplankton in the Tropical Ocean , 1983, Science.

[2]  W. Broecker,et al.  Fate of Fossil Fuel Carbon Dioxide and the Global Carbon Budget , 1979, Science.

[3]  D. Pimentel,et al.  The Potential for Grass-Fed Livestock: Resource Constraints , 1980, Science.

[4]  P. Ehrlich,et al.  Extinction, Substitution, and Ecosystem Services , 1983 .

[5]  G. Likens,et al.  Carbon in the biota. , 1973, Brookhaven symposia in biology.

[6]  T. Armentano,et al.  The role of temperate zone forests in the global carbon cycle , 1980 .

[7]  Tomas Frejka.  Long-term prospects for world population growth. , 1981 .

[8]  P. Demeny.  A perspective on long-term population growth. , 1984 .

[9]  G. Woodwell,et al.  A Comparison of Two Recent Estimates of Disturbance in Tropical Forests , 1985, Environmental Conservation.

[10]  C. S. Wong.  Atmospheric Input of Carbon Dioxide from Burning Wood , 1978, Science.

[11]  P. Ketner,et al.  Terrestrial primary production and phytomass , 1979 .

[12]  J. A. Mabbutt.  A New Global Assessment of the Status and Trends of Desertification , 1984, Environmental Conservation.

[13]  Terry L. Erwin,et al.  TROPICAL FORESTS: THEIR RICHNESS IN COLEOPTERA AND OTHER ARTHROPOD SPECIES , 1982 .

[14]  G. Woodwell,et al.  Changes in the Carbon Content of Terrestrial Biota and Soils between 1860 and 1980: A Net Release of CO"2 to the Atmosphere , 1983 .

[15]  P. Crutzen,et al.  Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning , 1980 .

[16]  A. Lugo,et al.  Biomass of Tropical Forests: A New Estimate Based on Forest Volumes , 1984, Science.

[17]  J. Molofsky,et al.  Assessment of temporal dynamics of selected terrestrial carbon pools. Final report , 1984 .

[18]  H. Odum,et al.  Primary Productivity of the Biosphere , 1978, Ecological Studies.

[19]  H. Mooney,et al.  The Determinants of Plant Productivity-Natural Versus Man-Modified Communities , 1983 .

[20]  B. Bolin,et al.  Changes of land biota and their importance for the carbon cycle. , 1977, Science.

[21]  David M. Sharpe,et al.  The ratio of total to merchantable forest biomass and its application to the global carbon budget , 1983 .

[22]  J. Sprent,et al.  Nitrogen Cycling in West African Ecosystems. , 1982 .