On Biomass and Trophic Structure of the Central Amazonian Rain Forest Ecosystem

Abstract

The importance of litter in the total energy flow dynamics of a central Amazonian rain forest near Manaus, Brazil, is discussed. The study area is located in the hinterland of Manaus between the Rio Negro and the Amazon. Its substrate is Tertiary sediment. The area receives 1771 mm rainfall per year, and the soil is classified as yellow latosol. The forest comprises 93,780 dicotyledonous trees and palms per hectare reaching 38.10 meters in height. Over 500 species of palms and dicotyledonous trees above 1.5 m. in height are identified for a 2000 sq. m. plot. The estimate for fresh living dicotyledonous tree and palm biomass is 939.5 metric tons per hectare consisting of 1.9% leaves, 49.7% stems, 21.3% branches and twigs, and 27.1% roots. Lianas, vascular epiphytes, and parasites are estimated to comprise 46.2 mt/hectare in the fresh state. At the soil surface there are 59 mt/hectare of fresh litter. Living animal biomass is about 200 kg/hectare of which half is soil fauna. The high proportion of soil fauna, the type of humus, the decomposition of litter, the apparent dependence of soil fauna on fungi, and the low nutrient content of litter are all factors which strongly support a consumer food chain based almost entirely on dead organic matter. The fungi play a decisive role in concentrating the otherwise limited nutrient resources. ECOLOGICAL STUDIES carried out in the Amazon region (Fittkau et al. 1969) raised further questions concerning the richness of the Amazonian ecosystems, the distribution of their biomass, and importance of overall as well as trophic-level structure. Additional experience obtained through later fieldwork in Amazonia and the results of our studies in hydrobiology, ecology, landscape ecology, pedology, and terrestrial production indicated the importance of finding out what the relationship of all these factors is in the entire central Amazonian' rain forest where the predominant soil type is latosol. Also considered must be the geochemical structure of that region, the division of the area as demonstrated by Fittkau (1969, 1970a, 1970b, 1971a, 1971b; fig. 1), and its influence on the nutrient supply available to the biomass in terrestrial and aquatic environments. A discussion of the bioenergetics of a tropical rain forest is difficult because few studies have been conducted either on the basis of the specific trophic levels involved or on the basis of the whole biomass. As a consequence, a discussion of available nutrients for specific species at various trophic levels is even more difficult. However, comparisons of litter-fall with the soil complex have been published, and the results are interesting enough to investigate the problem further. In a study by Klinge and Rodrigues (1968), the litter-fall of a central Amazonian tropical lowland rain forest was determined for 1963 and 1964. The average litter-fall for this period shows that 7.3 metric tons (mt) of dry matter per hectare (h) per year are returned to the soil. Dry matter per hectare is made up of 5.6 mt of leaves, or 76.6 percent of the total dry matter; the remainder is composed of flowers, small fruits, and twigs. It is interesting to note that this amount of litter is smaller than the litter-fall reported for tropical rain forests in Africa and Asia (Bray and Gorham 1964). Klinge and Rodrigues (1968) showed hat Amazonian litter is poorer in nutrients when compared with litter from other tropical forests. Results from our chemical analyses indicated that the following raw elements occur in the litter returned to the soil in central Amazonia (kg per hectare per year): 2.2 P, 12.7 K, 5.0 Na, 18.4 Ca, 12.6 Mg, and 105.6 N. In 1970, estimates were made of the amount of woody material involved in litter-fall of the central Amazonian rain forest (Klinge, unpublished). The results of the analyses show that one mt of stems (stem-part of plant between soil surface and first ramification), two mt of branches (ramifications without leaves), and 1.35 mt of twigs (ramifications bearing leaves), bark, etc. are involved. Because the 1963-1964 litter-fall experiment was not suitable for the measurement of the total fruit-fall, we calculated roughly the amount of fruits involved in annual litter-fall by kind, weight, and number of fruits in a 2000 m2 forest plot. Thus, we determined amounts of 0.35 mt of small fruits (up to 5 g in weight) and 0.5-1.0 mt of larger fruits (over approximately 5 g in weight). We 1 In this paper, 'central Amazonia' and 'central Amazonian' refer only to the ecological unit of Amazonia defined by Fittkau (1963) and illustrated in figure 1. 2 BIOTROPICA 5(1): 2-14 1973 This content downloaded from 157.55.39.243 on Wed, 05 Oct 2016 04:36:47 UTC All use subject to http://about.jstor.org/terms