358 REICHLE, DINGER, EDWARDS, HARRIS, AND SOLLINS 



permitted partitioning C0 2 flux between Oj litter, 2 litter, and soil (Edwards, 

 Van Hook, and Rau, 1971). Seasonal patterns of respiration corresponded 

 primarily to fluctuations in temperature and moisture (Fig. 2). Carbon evolved 

 as C0 2 from the forest floor was 1.04 kg/m 2 , with 55.4% of this total derived 

 from root and soil respiration, 29.5% from the Oi litter, and 15.1% from the 2 

 litter. Measured decomposer respiration was equivalent to 0.51 kg C m year , 

 and root respiration accounted for 0.496 kg C m year . This is similar to 

 forest-floor flux values of 0.71 to 0.79 kg C m 2 year for an oak forest in 

 Minnesota (Reiners, 1968) and considerably higher than the 0.41 kg C m 2 

 year x reported by Witkamp (1966) for a nearby oak forest in Tennessee. 



In contrast to in situ measurements of respiration by heterotroph decom- 

 posers, respiration of foliage-feeding insects was estimated from body-size 

 metabolism- regression equations (Reichle, 1971). Using mean body size for each 

 age-class for the various insect species (Reichle and Crossley, 1967), respiration 

 rates were calculated for herbivore and predator trophic levels. Total annual 

 respiration by herbivores amounted to 0.067 g C m year , and that for 

 predatory insects was 0.027 g C m 2 year . 



Litterfall and Tree Mortality 



Annual litterfall averaged 358 g (dry weight) m 2 year 1 (Table 3). Tulip 

 poplar leaves accounted for 61.3% of the total litter input, other leaves 28.9%, 

 twigs 5.2%, and reproductive parts 4.6%. Carbon content of 3 of 20 samples for 

 each collection period averaged 49.5% in tulip poplar leaves, 45.7% in 

 miscellaneous leaves, 47.0% in twigs, and 48.3% in reproductive parts. Using 

 these percentages an annual total carbon input to the forest floor by litterfall 

 was calculated to be 173 g C/m 2 . Seasonal patterns of carbon input to the forest 

 floor by litterfall showed an expected large input in the fall and a lesser input in 

 the spring. Spring litterfall consisted primarily of reproductive parts and twigs. 

 Carbon concentrations in individual groups showed no significant seasonal 

 patterns. 



Insect Consumption 



The loss of photosynthetic surface area in the canopy through insect grazing 

 varied between years, as well as during the growing season. In 1965, leaf holes 

 accounted for 5.6% of leaf area, although this was greater than the actual 

 consumption (1.9%) due to hole expansion in growing leaves. In 1966, loss of 

 foliage area was 10.1% (3.4% consumed); and in 1967 there was a foliage loss of 

 7.3% due to 2.5% leaf-area consumption (Reichle et al., in preparation). Within 

 a span of only 3 years, insect consumption varied by a factor of nearly 2. Foliage 

 production in the Liriodendron forest amounts to 186 g C/m 2 . Using a 50% 

 mean carbon content of leaves shows this flux to be 4.5 g C m" 2 year 1 . Aphids 

 return an estimated 0.5 g C m~ 2 year" 1 in honeydew, most of which is washed 

 off the surfaces of leaves by precipitation (Van Hook, personal communication). 



