ECOLOGICAL-STUDIES ON A LOWLAND EVERGREEN RAIN-FOREST ON MARACA ISLAND, RORAIMA, BRAZIL .1. PHYSICAL-ENVIRONMENT, FOREST STRUCTURE AND LEAF CHEMISTRY

1. Maraca, Brazil, is a large riverine island which is at the boundary between lowland evergreen rain forest and savanna. The island is now uninhabited but there is evidence that much of its forest (including the plots described in this paper) is secondary, dating from before 1880. 2. The mean annual rainfall is about 2300mm and there is a dry season from October to March. 3. Six replicate plots of 0.25 ha each were set up in the rain forest. Three of these were later felled, as part of a long-term study on forest regeneration, and three left undisturbed. 4. Soils were described from a profile pit and for surface samples (0-10 cm) in the three undisturbed plots. The soils were a Grossarenic Plinthic Paleudult (USDA). They were acid, had exceptionally low concentrations of total phosphorus, low concentrations of exchangeable cations but a fairly high base saturation, and a sandy texture. There was no surface root mat, no surface accumulation of organic matter, and no sign of podzolization. 5. All trees and lianas greater-than-or-equal-to 10 cm d.b.h. in the forest plots were enumerated, and structural features of the trees (including fine-root biomass) and smaller plants were quantified. The plots had a mean tree basal area of 23.8 m2 and the emergents were up to 40 m tall. 6. The mean tree species richness for the plots was forty per 0.25 ha and overall the Moraceae were the most important family in terms of basal area. 7. Analyses of leaves of 38 tree species showed wide interspecific variations but, in general, leaf nutrient concentrations were moderate or high. 8. It is concluded that although the Maraca forest occurs on very nutrient-poor soils it shows neither physiognomic nor foliar chemical features which are held to be characteristic of rain forests on such soils. Moreover, even though the soils are dry and sandy, the Maraca forest shows no features of heath forests.