CARBON FLOW AND STORAGE IN A FOREST ECOSYSTEM 361 



Root respiration rates may have been overestimated because the largest size 

 class used in respiration studies was ~3 cm in diameter, whereas many roots 

 included in the biomass estimates were much larger. Total root respiration could 

 have been overestimated due to decreasing respiration rate with increasing root 

 diameter. The budget value for litter and soil respiration (exclusive of root 

 respiration) was derived by summing all inputs of detritus and assuming no 

 annual increment in detritus. When added to the root-respiration estimate, CO2 

 evolution from the forest floor was estimated to be 1.02 kg C m year 



"0 — 1 



compared to the measured value of 1.04 kg C m year . This agreement 

 suggests that, in spite of the potential for revising estimated root respiration, 

 present approximations are realistic. The two independent estimates of carbon 

 translocation to roots differed by only 20% for all three groups of trees (yellow 

 poplar, other overstory, and understory), which is not serious considering the 

 preliminary nature of the data on which they are based. Annual root turnover is 

 probably underestimated, and it is not presently possible to determine the error 

 in estimates of branch and bole respiration of any species and of foliar gas 

 exchange for species other than tulip poplar. 



DISCUSSION 



Fundamental to analysis of the carbon cycle in ecosystems is an under- 

 standing of the functional relationships between photosynthesis, respiration, and 

 productivity of the system. Thus the annual increment of carbon in the 

 ecosystem or NEP (net ecosystem production) after Woodwell and Botkin 

 (1970) is 



NEP = GPP-(R A + R H ) 



where GPP = NPP + R A , and the equation may be rewritten in the form 



NEP = NPP - R H 



Solution of these equations, with quantification of the contribution of various 

 subsystem components to carbon pools and fluxes, is a primary objective of 

 ecosystem analyses. Relationships between pools and fluxes, seasonality and 

 variability of these parameters need to be explored by comparison of data from 

 different ecosystems. In this manner the pattern of carbon dynamics in 

 terrestrial landscapes will begin to unfold. 



The most comprehensively analyzed ecosystem to contrast with our 

 Liriodendron forest is the more xeric oak— pine forest at Brookhaven National 

 Laboratory (Woodwell and Botkin, 1970). The mesic Oak Ridge forest has a 

 total standing crop of 8.66 kg C/m 2 and a NPP of 685 g C m~ 2 year -1 . The 

 respective values for the oak— pine forest can be calculated from biomass and 

 estimated carbon content to be 5.96 kg C/m 2 and 598 g C m" 2 year" 1 . Relative 

 productivity, the ratio of NPP to standing crop, is higher in the oak— pine forest 



