CARBON IN THE BIOTA 295 



munities.) Growth efficiencies (new protoplasmic carbon/substrate carbon) for 

 reducers on land are probably higher overall than gross growth efficiencies of 

 animals. Growth efficiencies may be in the range of 30 to 40% for fungi of 

 decomposition, 5 to 10% for aerobic bacteria, and 2 to 5% for anaerobic 

 bacteria. If we use 20% as a reasonable intermediate growth efficiency for 

 terrestrial reducers, then total reducer production on land is of the order of 

 9.4 X 10 9 metric tons C/year and 23 times total animal secondary produc'tion. If 

 we assume a growth efficiency of 5 or 10% for marine reducers, then marine 

 reducer production would be 0.7 to 1.4 X 10 9 metric tons C/year, or about half 

 to about the same as our estimated marine animal production. Small size and 

 rapid turnover in bacterial cells and fungal hyphae make possible the massive 

 secondary productivity by these organisms that are obscure to us, and that in the 

 oceans probably have biomass much less than that of animals. It may not 

 be the case that biomass of fungi on land is small compared with that of animals. 



EFFECTS OF MAN 



We may ask finally what the effects of man's growth in population and 

 power are on world biomass and production. Biomass is reduced when perennial 

 grassland is replaced by annual crops and when grassland and shrubland are, with 

 erosion, degraded to desert-like communities. The greatest reductions of biomass 

 are those involving the greatest fraction of the world's biomass — the forests — 

 whether the reduction is by clearing for agriculture, urban and suburban spread, 

 increased fire frequency, or timber harvest. When old-growth forests are replaced 

 by plantations subject to harvest while still young, the average biomass of the 

 young stands is only a fraction of that of the old. A modification of Table 1 

 assigning the present agricultural lands to other ecosystem types and giving 

 higher biomass values for climax conditions to the forests suggests that world 

 biomass before the influence of civilized man was over 1000 X 10 metric" 

 tons C. The values in Table 1 are estimated as of 1950, before more recent, 

 systematic cutting in Amazonia and elsewhere in the tropics and intensive 

 harvest in the Temperate Zone. The rate of harvest of wood products, 20 ' 23 

 about 5X10 metric tons C/year, does not indicate the rate of forest clearing. 

 It is difficult to relate our estimates for forest production and biomass to the 

 FAO 20 ' 2 data for gross increment and growing stock in "the world's forests in 

 use" and the FAO's ". . .most serious warning. Changes in world forest 

 resources are slow, and there is in fact insufficient evidence to assert that the 

 present plantation programmes are making serious headway against the destruc- 

 tive pressures exerted on the forest by a fast-growing population." However, 

 the FAO 20 reported a world growing stock of 238 X 10 9 m 3 (including 

 bark) on 55% of the world's forest area in 1960. The carbon equivalent should 

 be roughly 110 X 10 9 metric tons C in all plant parts in reported forests and 

 plantations, a value markedly below our estimate for forests before the effects of 



