We analyzed the structure of a seasonally flooded beach-ridge forest and species functional characteristics regarding soil flood tolerance at Restinga da Marambaia (Rio de Janeiro). We sampled 50 contiguous 10 x 10m plots (0.5 ha) and recorded woody individuals with trunk breast height diameter (dbh) >2.5 cm. We found 1223 live trees, belonging to 24 families, 43 genera and 57 species. Shannon's index was 2.87 and equitability (J') 0.68. Total estimated density and basal area were 2446 ind.ha-1 and 25.14 m².ha-1. The most species-rich families were Myrtaceae (13), Leguminosae (5), Annonaceae, Euphorbiaceae, Myrsinaceae and Sapindaceae (4). Ten species had importance values (IV) over nine and included 75% of total IV. Species with high IV were Tapirira guianensis Aubl. (42.42), Amaioua intermedia Mart. ex Roem. & Schult. (40.77) and Chaetocarpus myrsinites Baill. (39.98), which together hold 41% of total IV. Results indicated that the tree community studied was mainly composed of species that prefer drier or periodically flooded soils, but not permanently flooded soils. The seasonally flooded forest in Restinga da Marambaia shows greatest similarity with seasonally flooded forests at Jurubatiba National Park - RJ (21.4%; 23.8%). Since the flora of seasonally flooded forests in southern and southeastern Brazilian restingas apparently is not restricted to these formations, it is reasonable to conclude that floristic pattern changes in the vegetation of these areas may be the result of the proximity of species' propagule sources (i.e., those with high soil flood tolerance), plus the phytogeography of the species linked to distribution limits caused by climatic conditions.
diversity; plant formations; phytosociology; similarity
