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Free keywords:
flora; floristic composition; saisonality; litter; phytosociology; Amazon
Abstract:
The present study was performed for 23 consecutive months (1974) in two adjacent plots in the Ducke Forest Reserve (02 degrees 35'S; 60 degrees 00'W), Manaus-Itacoatiara road, km 26, to the NE of Manaus, Amazonas. A brief description of the vegetation of both inventoried study plots is presented, including all trees alive measuring 20 cm or more in diameter at the breast height (DBH). This primary terra firme forest is very similar in its structure, physiognomy and floristic composition to the forest that generally is found surrounding Manaus. Its basal area was estimated in about 27 m(2) ha(-1) and its bole volume in about 230 m(3) ha(-1). Floristically the vegetation is very heterogeneous with no genera or species truely dominant. The Leguminosae sensu lato is the richest family in species and abundance followed by the Sapotaceae and Lecythidaceae. Sclerolobium melanocarpum DUCKE (about 24 %) and Enterolobium schomburgkii BENTH. (about 22 %) were the most important species with their respective Species Importance Values. The secondary vegetation originated from a primary forest that was cut 14 years ago and unburned. It mainly contained Cecropia sciadophylla MART. (about 115 %), Vismia cayennensis (JACQ.) PERS. (about 42 %) and Tapirira guianensis AUBL. (about 32 %), which are typical floristic elements of the late secondary vegetation. They compete only temporarily with other representative species of Amazon flora. The basal area was estimated in about 10 m(2) ha(-1) and the bole volume in 62 m(3) ha(-1). In the present study, it was found that leaves are the most prominent fraction of the litterfall in both communities and that there is relatively little interannual variation, particularly of the leaf-fall and the of total litter fall. Great variation of the annual amounts of non-leaf-litter was observed, which shows a clear seasonality of the leaf-fall. The fall of the other fine litter fractions shows a peaking which falls in the leaf-fall peak. Comparing the available data from the two types of vegetation studied, it was observed that both the total litterfall and the leaf-fall are obviously greater in the secondary forest. The apparent seasonality of the litterfall and particularly of the leaf-fall in the terra fume forest of Manaus area, both primary and secondary vegetation, agree well with the both previous results. The leaf-fall is generally greater in months that received relatively little precipitation. This study registered the maximum leaf-fall in both vegetation types in November and the flower-fruit fraction was greater in the months of maximum leaf-fall. An hypothesis is tested that the monthly leaf-fall is correlated with the monthly evaporation expressed as percent of the monthly rainfall. The annual average litterfall in primary forest was 7.9 t ha(-1) yr(-1), consisting of 6.0 t of leaves and 1.6 t of non-leaf matter (woody material, flowers, fruits etc.) and in the secondary vegetation was 9.0 t ha(-1) yr(-1), being 7.5 t ha(-1) of leaves and 1.6 t of non-leaf matter. The annual average percentage of fine litter fractions in the primary forest was 78.4 % of leaves, 15.7 % of woody matter and 5.9 % of flower+fruits and in the secondary vegetation was 81.7 % of leaves, 10.5 % of woody matter and 7.8 % of flowers+fruits.
