Análise da paisagem e estrutura das comunidades vegetais das formações pioneiras do Baixo Xingu, Pará.

Abstract

The hydroelectric Belo Monte Project will be built in the lower curse of the Xingu River in the Pará State. This will be second largest Brazilian hydroelectric, with a capacity of production of energy around 11.000 MW. In this project will be built a reservoir of the 400 km2, resulting in the flooding of the two forest types subject to inundation cycle of Xingu river. This vegetation is classified such as alluvial forests and pioneer formations, being the last vegetation analyzed in this dissertation and divided in two types: arboreal/shrub and herbaceus pioneer formations. This vegetation is subject to long periods of inundation and grows mainly in the islands of rock almost without substrate in the Xingu river channel. The objective of this study is estimate the habitat loss and characterized the species richness, diversity, structure and floristic composition of the pioneer formations in the Belo Monte Project. The Belo Monte Project is divided in the three sections in relation to levei of environmental impacts: Section 1 (without impact - control arca), section 2 (Xingu river reservoir, with impact of permanent flooding) and section 3 (with impact caused by reduced of the river flow due to construct of dam of the reservoir). The calculation of habitat loss was done with vegetation digital maps in the arca of the Belo Monte Project using Are view 3.3 software. The floristic inventory was carrying out using plots of 5 x 20 m in the arboreal/shrub pioneer formations and plots of 1 x 1 m in the herbaceous pioneer formation. The levei of habitat loss varied between the pioneer formation types. The construction of the Xingu river reservoir will lead to loss of habitat for up to 40% in vegetation (phytophysiognomie) subject to flooding at the section 2, which may reflect directly the reduetion of specimens of flora and fauna in the region. The variation of the habitat loss among the pioneer formation types included in the section 3 varied from 43% to 74%. In this case the main impact in the vegetation will be change of the reproduetion patterns that are related to the variation on inundation cycle of the Xingu river are will modified by construction of the dam. The total number of species found in the arboreal/shrub pioneer formations was 77 species varied from 37 to 43 species between the sections. There is significantly variation in the species richness, diversity, total density and total basal arca between the sections. However, the coefficients of regression are extremely low, explaining less that 8% of variation. In this case, to avoid type II error, these results should are use with precaution, being better considered the threes section equivalent in relation to parameters analyzed. There is no significantly variation of the floristic composition between the sampled plots in relation to three sections. The 10 more important species found in the in the arboreal/shrub pioneer formations in relation to relative density, frequency and dominance, totally more than 85%, 72% and 84%, respectively, being Myrciria florihunda. Conepia cataractea, Vitex cf. dukei, Campsiandra comosa, Acosmium nitens and Licania leptostachya found in the three sections. The 10 more important herbaceous species in relation to relative density and frequency totally more that 86% and 73%, respectively. There was no change in floristic composition pioneer formations between section sampled, thus, section 1, which will not suffer impact of enterprise, can offset the impact that will be submitted the pioneer formations herbaceous and arboreal-shrub found at the section 2 and 3.