310 



REINERS 



TABLE 2 



A FIRST APPROXIMATION OF CARBON TURNOVER IN 

 TERRESTRIAL DETRITUS* 



*Based on Whittaker and Likens' estimates of world net primary production 40 and my 

 own estimates of the percentages of net production which enter detritus pools in ecosystem 

 types. 



my weighted value for energy flow to detritus pools for this combined group is 

 90%. 



The percentages for tropical, temperate, and boreal forests are for 

 steady-state systems in which there is no further biomass increment. In young 

 forests this percentage is much lower (52% in 40- to 50-year pine— oak and 

 oak— maple stands). 42 ' 44 



The 80% estimate for detritus in woodlands and shrublands is based on the 

 assumption of higher browsing levels plus periodic losses to fire. In savannas, fire 

 may take all grass shoots and tree leaves every year, 45 or grazing may be 

 severe. Grazing and fires are also regular processes in temperate grasslands. 

 Kucera and Kirkham 2 stated that the principal source of detritus to the soil in 

 their tall-grass prairie study area was the root system. Although the shoots might 

 decay on the surface as mulch, apparently fire was a regular removal factor. 

 Actually, grazing may be the most serious of these two factors today because 

 much of the areas that were most frequently burned is now under cultivation 

 and the remainder is heavily utilized for domestic animals. 



Considerable variation doubtless exists between types of tundra with regard 

 to energy-flow pathways. Grazing may be periodically heavy in some types of 



