Perfil florístico e distribuição das espécies vegetais, em relação ao gradiente de umidade do solo, em seis veredas no Triângulo Mineiro

Abstract

The aim of this study was to verify the vegetation distribution along the gradient of moistness of the ground in six palm swamps in the municipalities of Uberlândia and Uberaba. A floristic survey and the water layer depth and soil textures were also evaluated. Three of the studied palm swamps (V1, V2 and V3) are located in the geomorphological surface with 800-842 width, covered with Latosols of Medium Texture. The others (V4, V5 and V6) are situated on areas 922-940 m high on very argillaceous texture soil. The studied area in each palm swamp was equivalent of 100 m along the slope (right and left) through the width of the palm swamp. A floristic survey was done, from January 2002 to January 2003, in random walks on determined tracks. The water layer depth was determined in one year, in three trans-sections, with sampling points on each zone of the palm swamp (edge, middle and back), in the same area where the vegetation was characterized. To determine the soil texture, samples was collected in each of the zones of thee palm swamp, in a deep from 0 to 20cm. The floristic survey revealed 435 species, belonging to 197 genders and 62 families. In the palm swamps V1, V2 and V3 322 species were found, whereas 300 species were encountered on the palm swamps V4, V5 and V6. The nine richest families account for 63,7% of the total species observed. Cyperaceae, Eriocaulaceae, Poaceae and Xyridaceae had occurred with more species in the zones of the middle and the back, while Asteraceae, Melastomataceae and Rubiaceae, were prevalent in the edge and the middle. The ordinance done for the multidimentional scheduling - MDS, from the floristic similarities between three zones of the palm swamps, showed higher similarity between the middle and the back, then with the edge. It was also verified that the edge zones of the palm swamps was less similar between themselves, then the middle and back zones. The analyses of the principal components (PCA), performed utilizing data from the 44 species that occurred in at least five of the studied palm swamps, showed that Axonopus siccus, Hyptis linarioides and Tibouchina gracilis, are related with the edge of the palm swamps. Ten species had been distributed in the middle zone, among them: Paspalum cordatum, Rhynchospora globosa and Syngonanthus xeranthemoides. And finally, ten species were distributed in the back zone, among them: Eryngium ebracteatum, Trimezia violacea and Xanthosoma striatipes. The average depth of the water layer generally had been higher in the edge and smaller in the back zone. April was the month that showed the smallest values of water layer depth, and August and September, the highest ones. In the palm swamps V1, V2 and V3 the percentage of sand in the soil was higher than the other ones. On the other hand, the palm swamps V4, V5 and V6 presented soils with the highest amount of clay, mainly in the edge and the middle regions. The differences in the number of species between the two types of palm swamps are possibly due to human influence and/or as a consequence of the small area showed in each palm swamp. The difference between the depth of the water layer and the ground texture seems to be less relevant in this case.