Classification and ordination of plant formations in the Pantanal of Brazil.
Phytosociological data were collected for 10 physiognomically distinct plant formations during the rainy, flood and dry seasons in the seasonally flooded plain of the Brazilian Pantanal. The degree of association among plant species was measured with the Jaccard similarity index, and both the Jaccard similarity index and the Bray Curtis distance index were employed to classify sample units into similar groups. The ordination of plant species and sample units was performed using Correspondence Analysis. Four groups of plant formations were significantly distinct on a quantitative basis: marsh ponds/waterlogged basins, short grasslands, tall grassland/scrub, and forest edges. These formations were ordered along a gradient of topographic relief from depressions with permanent standing water (marshes) through plains subject to seasonal flooding (grasslands and scrub) and mounds of sandy soil above the flood level (forests). Although the duration of standing water appeared to be one of the most important variables, it is suggested that the distribution of plant species within wetlands is probably explained by the interaction of many additional factors.