296 WHITTAKER AND LIKENS 



man (world biomass of 1000 X 10 9 metric tons C, X 90% for forest biomass, 

 X 55% for corresponding area, is 500 X 10 metric tons C). 



It appears that world biomass is being effectively reduced as older growth 

 forests are replaced by younger growth and clearings, but we cannot estimate the 

 rate of this process. Probably the amount of carbon being held in organic forms 

 is being reduced also by the reduction in organic content of soils that follows the 

 clearing of natural vegetation. 2 5 Biogeochemical consequences include not only 

 those on the carbon cycle itself but the more indirect contribution of biomass 

 reduction and erosion to the increased transfer of nutrients from land surfaces to 

 water bodies. 



Man's relation to world productivity is, like his relation to nature, 

 ambivalent. Irrigation may increase land production and erosion reduce it; 

 increase in atmospheric carbon dioxide may enhance production whereas that of 

 other pollutants reduces it; fertilization increases land production whereas 

 fertilizers and toxins from the land may reduce useful aquatic production. Only 

 by detailed study, and then with uncertainties, could one assess the balance of 

 these effects and the rate at which the balance is shifting. Increase in 

 productivity of man's crops is, on the whole, slow, difficult, and demanding and 

 at best keeps pace with population growth or falls somewhat behind. The 

 contamination and toxication of the biosphere are, in contrast, accelerating at a 

 rate reflecting the much more rapid growth of technology, as this rapid growth is 

 made possible by fossil fuel and other power sources. The terms of the race 

 imply that the influences toward reduction of productivity should in due course 

 prevail. We are not suggesting that the time is here or that man's food 

 supply — except, perhaps, for the marine fisheries — is now limited by these 

 effects. 



Most of the biosphere's net production is not suitable, or not harvestable, for 

 human food. Man harvests (in 1970) about 5.5 X 10 8 metric tons C in cereals 

 and other plant foods, 21 ' 81 somewhat more than one-hundredth of land 

 production, from arable lands now producing somewhat more than one-tenth of 

 land production. Man is now harvesting animals for food to the amounts of 

 about 33 X 10 6 metric tons C/year (including milk and eggs) on land and 

 7.5 X 10 6 metric tons C/year from water bodies. 21 ' 22,81 These yields are 

 currently increasing at rates larger than that of population growth. The other 

 side of the ambivalence is present only in incipient form, in the known reduction 

 of plant growth by air pollution in major urban areas, 27,39 and suspected effect 

 of acid rain (from pollutant S0 2 and NO x ), discussed by Hill in reducing 

 growth of forests in northwestern Europe and northeastern United States. We 

 suggest that food production on land can still increase for some time but that 

 with continued growth of industry a widespread reduction of biosphere 

 productivity, at present inconspicuous but in the future accelerating, should be 

 expected. 



The biosphere is now increasingly vulnerable to widespread, adverse 

 influences of human industry. Industrial society may also be increasingly 



