The floodplains under the influence of the Amazon basin cover an area of over 300,000 Km2, corresponding to 6% of the Brazilian Amazon, with a high degree of environmental variation, due to differences in chemical, physical, biological factors and flooding regime. The study was developed in the high and low floodplains of Taiassuí stream (1°24'51.7 "S, 48°14'0.9 "W), a tributary of the right bank of the Guamá River, Benevides-Pa. Floristic inventories were conducted on two hectares in each floodplain type. The differences are determined by topography (2-4 m difference in level between high and low várzea) and flooding regime. Each hectare was divided into 25 plots of 20 x 20 m (400 m'). All trees, lianas and palms with DBH>10cm were included. The objective of this work is to perform a comparative analysis of the structural and floristic variations of these environments. In the high floodplain, 517 individuals, 90 species and 34 phanulias were found. The most abundant were Tricbantbera gigantea (Bonpl.) Nees (Acanthaceae), Pentacletbra macroloba (Willd.) Kuntze (Mímosaceae) and Astrocaryum murumuru Mart. The species with the highest Mfor were Iriartella setigera (Mart.) H. Welldl. (Arecaceae), Pentacletbra macroloba (Willd.) Kuntze (Mímosaceae) and Astrocaryum murumuru Mart. The Shannon-Weiner diversity index was 3.78 nats. In the low floodplain, 525 individuals, 117 species and 38 families were recorded. The most abundant were Tbeobroma subincanum Martius in Buchner (Sterculiaceae), Zygia latifolia (L.) Fawc. & Rendle (Mimosaceae) and Pentaclethra macroloba (Willd.) Kuntze (Mimosaceae). The species with the highest M were Theobroma subincanum Martiusin Buchner (Sterculiaceae), Zygia latifolia (L.) Fawc.& Rendle (Mimosaceae) and Pentaclethra macroloba (Willd.) Kuntze (Mimosaceae). The Shannon-Weiner index was 3.84 nats. The lower floodplain of Taiassuí showed higher abundance and diversity when compared to the upper floodplain, although under conditions of greater water stress; the upper floodplain, although under more favorable environmental conditions, showed lower indices. Evidence of anthropic action was found in the high floodplain, which may justify the results obtained in this study.
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