The objective of this work was to study the effect of topography and rainfall in the structure of trees and litter production in a tropical rain forest in the National Forest of Caxiuanã. Were delimited three tranches of 1.000 m2 in each topographic levels (lowland, intermediate and plateau) and identified all individuals and collection of litter. For the three levels was recorded a total of 124 species belonging to 33 botanical families. The three families with higher importance value index for topographies of lowland and intermediate were Sapotaceae, Lecythidaceae and Chrysobalanaceae and for plateau were Lecythidaceae, Sapotaceae and Chrysobalanaceae. The species Lecythis idatimon Aubl., Rinoria guianensis Aubl. e Eschweilera coriacea (DC.) S.A. Mori. showed the greatest importance value indices for the three topographies. The seasonality affects significantly the litter production, showing the highest values at the end of rainy season and early dry season. The environmental stimulus for the fall of the leaves is mainly due to decrease in relative humidity, justified by the need of the plants to increase photosynthetic efficiency. The difference in population structure show strategies for flower production, and consequently the dispersion of fruits and seeds.
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