The object this study was to study the effect of topography and microclimate (temperature and precipitation) in the floristic and structure of trees and litter production in a tropical rain forest in the National Forest Caxiuanã. In the grade of 25 km2PPBio, three areas were chosen (A, B and C) where plots were established 10 x 100 m, following the same topographic profile (lowland, intermediate and planteau). These plots, we identified all trees with DBH ≥ 10 cm for the realization of phytossociologic, taking into account the parameters of absolute and relative density, frequency and dominance, thus calculating the index value of importance (IVI). Micrometeorological temperature data were obtained from connected data logger Hobo Pro v2 and precipitation data were collected by the automatic station of IBAMA. We found 124 species in 33 plant families. The richest families in number of species were Sapotaceae (17), Chrysobalanaceae (10), Lecythidaceae (10) and Caesalpiniaceae (8). The most abundant families in number of individuals were Sapotaceae (65), Chrysobalanaceae (52) and Caesalpiniaceae (40). The area showed little floristic diversity evidenced by the low Shannon Diversity Index (H’= 3.16) and high uniformity in the proportions individuals/species within the plant community, given the degree of evenness of Pileou (J’= 0,94). There were no significant differences in richness and diversity of trees in relation to the plateus, intermediate ans lowland, as well as the density of species and basal area individuals. No there was a clear separation in the composition of tree species (DBH ≥ 10 cm) between the plots sampled in the plateau topographic condition, intermediate and lowland. The family with the higest IVI was Sapotaceae for the topography of lowland and intermediate, and Lecythidaceae for the plateau and species with higher IVI for three topographies were Lecythis idatiomon, Rinoria guianensis and Eschweilera coriacea. The average production of total litter in the nine plots was 758.59 kg ha-1. There was no significant difference in the production of litter in relation to topography and medium temperature and maximum temperature, but in relation to rainfall and minimum temperature there was differences. The leaf fraction (73,55%) was the most representative in the composition of litter, followed by branches (24,98%), fruits (3,88%) and flowers (3,85%). The flower production and fruits showed no significant relationship with the topography. No relationship was found in flower production with rainfall and temperature, but the fruits production showed significant differences with precipitacion and maximum temperature and minimum. The topography does not influence the floristic and structure of trees and litter production in the nine studied plots, but the variation in precipitation and temperature had a strong influence on litter production total and fruit production.
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