Estrutura de populações de Xylopia aromatica (Lam.) Mart. (Annonaceae) e Roupala montana Aubl. (Protecease) em quatro fragmentos de cerrado sensu lato no municipio de Itirapina/SP

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The population structure of two species, Xylopia aromatica and Roupala montana, has been studied in four fragments of cerrado in Itirapina, SP, SE Brazil, with different physiognomies and disturbance histories, and in three areas of similar physiognomies within the same fragment. Within each fragment a grid of 200-contiguous-plots 5 x 5 m has been installed, totaling 0.5 ha. In each plot, all individuals of these two species, with a stem diameter at the height of the soil (DSH) ? 3 cm have been marked and their height and DSH recorded. In 1- m2 sub-plots, chosen among the vertices of each 25-m2 plot, individuals with DSH <3 cm have been marked. For each species studied, six ontogenetic stages have been identified: seedling (presented one or two cotyledon leaves), young 1 (did not present cotyledons or ramifications), young 2 (presented ramifications), immature (presented ramifications and reiterations), vegetative adult (presented equal or larger diameter and height than those of the smaller reproductive individual, but did not reproduce during the sample period) and reproductive adult (presented flower, fruit or scar of these structures). A great plasticity of the architectural form was observed among the species studied here, and these variations were greater among the fragments with most forest physiognomy and open ones. This suggests that, depending on the characteristics of growth and on the resistance and/or reproductive strategy adopted by the species in face of a disturbance factor, different architectural forms can be found. We have found a higher proportion of initial stages of Xylopia in disturbed areas with open physiognomies, whereas Roupala presented high proportion of Jo1 and Jo1:AR in Valério 1, wich present most forest physiognomy. The predominance of different stages and the different proportions among the stages generated different population structure in both species, among fragments with different physiognomies as well as within the same fragment. These differences could have been influenced by the disturbance history and by the reproductive characteristics such as phenological pattern and type of reproduction. The spatial distribution of the ontogenetic stages of the two species differed among areas, being the differences greater among areas within the same fragment. Xylopia presented random spatial pattern at all stages, except for the later stages, in forest physiognomy fragment (Valério), in which the pattern was aggregated, while Roupala presented predominance of clumped pattern in all stages. These differences among the spatial distributions can be a consequence of the variation in environmental conditions, mainly of luminosity, or the influence of other factors not studied here. It was observed that Xylopia was present in all fragments, whereas Roupala wasn?t, indicating an aggregated pattern to Roupala among fragments and, both species presented lower density in open fragments, leading to the inference that disturbances, phenological patterns and type of reproduction are likely to be responsible for the spatial distribution of the species among the fragments and for their densities. Finally, differences in the rchitecture and in ontogenetic and spatial stage structure, as observed in this paper, lead to the conclusion that studies focusing on spatial variations within and among areas and the haracteristics of species and their habitats are of fundamental importance to understand better which factors influence the population processes, their importance in different places and their consequences. Thus, the importance of preserving as many fragments as possible gains eminence in this context, as suggested by a number of researchers, since each area of cerrado constitutes an environment that can contribute to the success of the species. Moreover, means of restraining disturbance, such as cattle removal, indiscriminate fire control, building of clearings, are fundamental in the fragments where these disturbances are frequent.

ASSUNTO(S)

plantas cerrados alometria ontogenia

ACESSO AO ARTIGO

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