362 REICHLE, DINGER, EDWARDS, HARRIS, AND SOLLINS 



(10%) than in the tulip poplar forest (8%). The R A by the oak-pine forest is 

 lower at 675 g C m" 2 year -1 than the tulip poplar forest at 941 g C m 2 year 1 , 

 and the respective ratios of Ra to standing crop are identical at 0.11. The GPP 

 by the Oak Ridge forest was at least 1.63 kg C m year compared to 1.36 

 kg C m" 2 year" 1 for the Brookhaven forest, although the respective ratios of NPP 

 to GPP were essentially identical at 0.42 and 0.45. 



Estimates of NEP for the two forest ecosystems were substantially different. 

 The NEP for the open oak— pine forest was between 271 and 294 g C m year 

 (depending on whether allometric or gas-exchange values were used to make the 

 calculation), and NEP for the Liriodendron forest was 161 gC m year . 

 Although the tulip poplar forest had higher GPP and NPP, its higher total Rg of 

 1.47 kg Cm" 2 year (compared to 1.01 kg C m 2 year for the oak— pine 

 forest) resulted in a lower NEP. The higher relative respiration of the 

 Liriodendron forest (Rg/NEP) of 9.1 compared to approximately 3.6 for the 

 oak— pine forest reflects several fundamental differences between internal 

 components of the two ecosystems. 



The distribution of standing crop between aboveground and belowground 

 components of the two forests varies severalfold. Whereas the oak— pine forest 

 with a standing crop of 5.96 kg C/m 2 has an aboveground to belowground ratio 

 of 1.8, the tulip poplar forest has a ratio near 4.2 for its biomass of 8.66 kg C 



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m year . Generally, the respiration of belowground woody components, 

 primarily fine roots, is higher than that of nonphotosynthetic aboveground 

 biomass. The Rh in the mesic Oak Ridge forest (524 g C m year ) was nearly 

 twice that of the more xeric forest at Brookhaven. This discrepancy was not 

 simply due to the magnitude of the Rg values but rather to a more basic 

 apportionment of Rg between R A and Rpj ; the ratio of R^/Rh f° r tne 

 oak— pine forest was 2.5 but only 1.8 in the tulip poplar forest. In these 

 parameters may lie one fundamental difference in NEP between the two forest 

 ecosystems. 



Although the tulip poplar forest annually loses 522 g C/m through decay, 

 the oak— pine forest turns over only 360 g C m 2 year l . For the mesic 

 deciduous forest, decay amounts to an annual turnover of 4.1% of the detritus 

 carbon pool of 12.85 kg C m 2 year 1 . Approximately 60% of the total carbon 

 in the tulip poplar forest (21.51 kg C/m 2 ) is in the detritus pool. With an 



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estimated NEP of 161 gC m year and an annual woody increment of 168 

 g C m year , the carbon pool in litter and soil detritus remains in equilibrium 

 according to our initial conditions. This would not be so for the oak— pine 

 ecosystem, where a higher NEP to standing-crop ratio of 0.05 to 0.02 for the 

 tulip poplar forest reflects continuing increase of carbon pools in both standing 

 crop and soil organic matter. The sources and rates of carbon accumulation in 

 soil are multiple. In the Liriodendron forest, annual decomposition respirator)' 

 losses account for 522 g C m" 2 year" 1 ; 228 g C m~ 2 year" 1 from litterfall, dead 

 bole and frass inputs is less than the additional 294 g C m" 2 year ' root death 

 required to keep the detritus carbon pool in equilibrium. Independent estimates 



