Classification and ordination of plant formations in the Pantanal of Brazil

Classification and ordination of plant formations are presented for a seasonally flooded plain of the Brazilian Pantanal. Phytosociological data were collected on 10 physiognomically distinct formations during the rainy, flood, and dry seasons. The degree of association among plant species was measured with Jaccard similarity index, and both Jaccard similarity index and Bray Curtis distance index were employed to classify sample units into similar groups. The ordination of plant species and sample units were performed with 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 flats subject to seasonal flooding (grasslands and scrub) and mounds of sandy soil above the flood level (forests). Although hydroperiod appears to be one of the most important variables, the distribution of plant species within wetlands is most probably explained by the interaction of many additional factors. A few plant species could be used as indicators of the local hydrological and edaphic conditions, e.g., Eleocharis elegans, Aeschynomene fluminensis, Hydrolea spinosa, and Hymenachne amplexicaulis for marsh ponds, and Caperonia castaneifolia, Diodia kuntzei, and Eleocharis acutangula for waterlogged basins. The procedure presented in this study could be developed as a tool for the inventory and management of the Pantanal and other palustrine wetland habitats.