Floristics, structure and soil-vegetation relationship along a phytophysiognomic gradient on canga at Serra Sul, National Forest of Carajás - Pará / Florística, estrutura e relações solo-vegetação em gradiente fitofisionômico sobre canga, na Serra Sul, FLONA de Carajás - Pará

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The vegetation associated with Ferruginous rock outcrops, commonly observed in the Carajás mountains and Quadrilátero Ferrifero, can be included within the concept of Rocky Fields, being called Ferruginous Fields (Campos Ferruginosos). These are, in turn, formed by a number of types (facies), influenced by environmental attributes such as: soils, water avalability, landscape position and conectivity with neighbour environments, amongst others. Little studies have been made to clarify the importance of abiotic factors to this vegetation and its diversity. The aims of this work were: (1) determine the floristic composition and phytossociologic structure of a sector along a gradient from Forest to Ferruginous Rock outcrops, all developed from high grade ironrich canga; (2) to analyse the vegetation in relation to soil properties.For the analysis of species (phytosociology) 96 plots were demarcated to address all environmental units: Open Rocky Field, with 40 plots randomly distributed of 1m2 area, determing life forms, species composition and species cover; Scrubby Rocky Field, with 40 plots of 25 m2, sampling the individuals with CAS ≥ 3 cm. In the Forest both internal and external, 8 plots of 100 m2 were sampled, encompassing all individuals of CAP ≥ 10cm at 1.3 m above ground, estimating their heights. In the open rocky vegetation, soils sampling was undertaken from the nearby área at the surface (0-10cm) and litter, to avoid disturbance in the plot. In the forested areas, sampling was carried out within the plots. Linear Correlation coefficients were calculated between soil chemical properties and litter, and statistics tests were performed (variance analyses-ANOVA) and Tukey test at 5% probability. A cannonical correspondence analysis was also undertaken. A total of 166 species was obtained, distributed for 104 genera and 56 families. These families had the following decreasing order of richness: Fabaceae (19), Euphorbiaceae (10), Melastomataceae e Sapindaceae (9), Myrtaceae (8), Rubiaceae (6), Annonaceae, Bignoniaceae, Bromeliaceae, Malpighiaceae, Nyctaginaceae, Poaceae and Salicaceae with 4 species each. Phanerophytes were the dominat life-forms. The formations displayed significant differences in relation to species richness.based on soil chemical analysis, all phytophysiognomies showed very acid soils, with low levels of P and nutrients. The organic matter content and soil depth were key variables for explaining the occurrence of these phytophysiognomies. The CCA analysis enabled to distinguish three different groups, corroborating the prominent contrast between the different physiognomies developing on Canga at Carajás, since each one exibit characteristic species with low share, in function of soil properties. Water availability and soil depth should represent the most importanat factor to explian the gardient, but further studies will clarify its quantitative influence.

ASSUNTO(S)

características fitofisionômicas canga ferrífera ironrich canga rocky field savana metalófila campos rupestres botanica phytophysiognomic properties

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