Estudo floristico e fitossociologico de um gradiente altitudinal no planalto residual do Urucum - Mato Grosso do Sul - Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

This is a structural and floristic study of an altitudinal gradient on the Urucum plateau, Mato Grosso do Sul, Brazil. This study is divided into three chapters: The first deals with floristic, structural and diversity variations in trees and shrubs and their relationships with the environmental features associated with altitude; the second deals with the variation in vertical structure of the vegetation at different altitudes and the third describes the floristic composition of the vegetation including all life forms of angiosperms found. Five areas were established, at different altitudes. The first at 100 m altitude, on a plain, and the rest on Santa Cruz hill at altitudes of 200, 400, 600 and 800 m. In each area twelve 30x30 m plots distributed in three 30 x 12 m blocks were established, totaling 5.4 ha. These blocks were positioned perpendicular to the slope direction. All trees and shrubs, with branch circumferences at 1.3 m above soil summed 15 cm or more, were sampled. The height of the individuals was estimated by comparison with a rod of known size. Fifteen soil samples between 0 and 20 cm depth were collected in each plot. These samples were then mixed to give a single sample per plot and used for nutrient and granulometric analyses. The rainfall was estimated using data from rain collectors at several altitudes on hills in the region. In adittion, all angiosperm life forms found with flowers or fruits were collected. These collections were performed inside and around the plots and along the roads and paths used to access them. The plants were collected according to the usual methods in Botany and deposited in COR herbarium. Identification was performed consulting bibliography, herbarium material and specialists. A total of 419 species belonging to 289 genera and 89 families were found. The richest family was Leguminosae with 55 species (21 Faboideae, 20 Mimosoideae and 14 Caesalpinioideae), followed by Bignoniaceae, Euphorbiaceae and Orchidaceae with 17, Sapindaceae with 16, Asteraceae with 13 and Rubiaceae with 12. The trees, shrubs and palms summed 239 species (57 %); herbs 78 species (18.6 %); vines 69 (16.5%); epiphytes and hemiepiphytes 29 (6.9%); parasites and hemiparasites 4 species (1%). In the phytosociological study a total of 6093 individuals of 169 species were sampled. There was a gradient in the soil nutrients level along the altitude variation except in the area at 200 m. This gradient was related to soil depth where, with exception of the area at 200 m, the shallow soils were at higher altitudes and the deeper ones were found at the base or intermediate areas. The number of species at each altitude varied from 49 to 79 with no clear tendency with altitude. In terms of floristic composition there were two main vegetation groups corresponding to the deciduous forest up to an altitude of 200 m and the semideciduous forest between 400 and 800 m. These variations in floristic composition were influenced mainly by the variation in precipitation and, in a smaller degree, by the depth of the soil. The area at 400 m altitude was an ecotone with intense interchange of species and predominance of semideciduous forest species. The density of trees and shrubs was greater at the lowest and the highest altitude areas whereas the total basal area was greater at intermediate altitudes. The highest importance values for each altitude in altitudinal increasing order was reached by Acosmium cardenasii, Acacia polyphylla, Attalea phalerata, Protium heptaphylum and Guapira areolata. The vertical structure of the areas studied was, in general, composed by of three layers: The first was discontinuous and constituted by the canopy and emergent species; the second was continuous and constituted only by canopy species and the third was the understorey. Only the area at 600 m altitude presented two layers: the canopy and the understorey. The number and importance value of the autochoric species decreased with increasing altitude. The importance value of the anemochoric species decreased while the zoochoric species increased with increasing altitude. These tendencies were interpreted as influenced by the humidity variations along the gradient

ASSUNTO(S)

floristica altitude - influencia floresta estacional

ACESSO AO ARTIGO

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