Matas de galeria no Parque Nacional de Sete Cidades (PNSC), Piauí, Brasil: fitossociologia, diversidade, regeneração natural e relação com variáveis ambientais

Abstract

The present study was realized in the Sete Cidades Nacional Park (PNSC), located in the north east section of the Piauí state. The park, considered a priority area for the conservation of the Cerrado biome (BRASIL 1999), contains a mosaic of physionomies and occurs in an area of ecological transition. This study is part of the 2nd stage of the scientific excursion of the project Biodiversity and Fragmentation of Ecosystems in the Cerrado Margins of the North East (Site 10 of PELD), with support from CNPQ/BIOTEN and undertaken by the Federal Universities of Piauí (UFPI) and Brasília (UnB). The objective was to study the floristic composition, fitosociology, diversity, natural regeneration and the relationship with enviromental variables of the tree vegetation in the gallery forests that are distributed along the river courses located in the PNSC and also evaluate the floristic similarities between these forests and others in diverse localities in the Cerrado biome. The trees (DAP > 5 cm) were sampled systematically in 56 permanent plots of 100 m2 (10 x 10 m) in four sections of gallery forests in the Park. At each forest, the plots were subdivided in subplots of 5 x 5 m and 2 x 2 m, for sampling the natural regeneration of the tree vegetation (DAP < 5 cm) (saplings and seedlings respectively). Soil was collected (0 – 20 cm) (for physical and chemical analysis) and a subjective description of the inundation in each plot was made, forming the environmental variables. To evaluate the hypothesis of spacial heterogeneity of the biota in the gallery forests of the Sete Cidades Nacional Park (PNSC), Piauí, and its determinant factors, correlations between the distribution of tree species and enviromental variables was verified, by a CCA (Canonical Correspondence Analysis) ordination and a TWINSPAN (Two - Way Indicator Species Analysis) classification. The 642 tree individuals sampled were distributed in 75 species, 64 genera and 30 families. The absolute density was 1.146,43 ind haֿ1 and the basal area was 26.55 m2 haֿ1. The alfa diversity obtained by the Shannon - Weiner index (H’) was 3.53 nats indֿ1 and the Pielou equability (J’) was 0.82. The beta diversity between areas, analised by similarity indices, and the beta diversity between the Park and other locations, using the TWINSPAN method, was high. The diameter distribution for the comunity was in the form of an ‘reverse J’, indicating that the community and the most abundant populations are self - regenerating. The multivariable analyses showed a high beta diversity or dissimilarity between the PNSC gallery forests sampled areas, confirming the hypothesis of enviromental heterogeneity. The TWINSPAN and the CCA showed coherent results, showing the formation of two distinct vegetation groups in the area, where the flooding or non - flooding soil was the most important variable.