TERRESTRIAL DETRITUS AND THE CARBON CYCLE 319 



TABLE 5 (Continued) 



Detritus input, 

 metric tons ha" 1 year" 1 



Total 

 carbon 



Below- turnover, 



Ecosystem Location Ref. Aerial ground Total 10 9 tons 



Agricultural Land (14 x 10 8 ha) 



6.5 tons/ha average 40 3.3^ 2.3 



production x 0.5 



Total carbon turnover 37.5 



a Based on Whittaker and Liken's estimates of land area occupied by ecosystem 

 types, 40 plus selected data on detritus input from the literature. Necessary assumptions 

 underlying some of the estimates are given. Carbon has been assumed to equal one-half 

 detritus dry weight. 



b Belowground contribution is assumed to equal 30% of total. 



c Belowground contribution is assumed to equal 25% of biomass yielding ~30% of total. 



Belowground contribution of wetland forest is assumed to equal 10% of total. 

 e Includes timberfall. 

 Averages of numbers of stands given. 

 ^Weighted by numbers of stands comprising original averages. 



"Belowground contribution is assumed to be 10% of total (see Ref. 49, Table 46). 

 'Belowground contribution is assumed to be 14% of total (derived from 11 stands in 

 Ref. 49, Table 32). 



JOriginal data in terms of carbon; doubled for estimate of dry weight. 

 Belowground contribution is assumed to be 50% of total (derived from 11 spruce 

 stands in Ref. 49, Table 13). 



The eight examples chosen are numbers 12 through 20, excepting No. 18. 

 m Belowground contribution was estimated in proportion to root biomass (74% of total 

 in Calluna in Ref. 69). This was apparently the basis of computation for Russian woodlands 

 cited above. 



"Assuming 100% of maximum shoot standing crop goes to detritus as with the Russian 

 data. 



°The nine examples chosen were numbers 1 through 9. 



PRoot growth is assumed to be 50% of total, and 100% of shoot growth is assumed to 

 become detritus. 



^Same estimate as in Table 2. 



Two estimates from the literature can be compared with these approxima- 

 tions. Plass 5 prepared a partial carbon budget for the world, in which he 

 estimated that photosynthesis and respiration plus decay balanced at 60 X 10 9 

 tons of C0 2 . It is unclear if his photosynthesis has been corrected for plant 

 respiration, but assuming it has, the respiration of all heterotrophs is 16.4 X 10 9 

 tons C/year. If this is added to his estimate of loss of stored carbon from 

 cultivated lands, carbon flux from total respiration is only 17 X 10 9 tons C/year. 



Bolin estimated a flux of 25 X 10 9 tons C/year through the terrestrial 

 detritus pool. Both of these estimates are lower than the four approximations 



