Florística e estrutura da comunidade lenhosa e herbácea de uma savana rupestre no sudoeste do Amapá, Brasil

Abstract

The rupestrian savannah is a physiognomic type characterized by rocky outcrops, poor in nutrients in the soil and that in Amapá, occurs only in the Extractive Reserve (RESEX) Rio Cajari, southwest of the state of the state. There are few studies on floristic composition and diversity that assess the influence of edaphic factors on the similarity of woody and herbaceous species in rocky savanna. Therefore, this study aims to analyze the floristic composition, structure, richness and diversity of the woody and herbaceous community of an area of rupestrian savannah in the Extractive Reserve (RESEX) Rio Cajari, and to verify which edaphic factors influence the similarity of species in the communities. For the sampling of woody individuals, nine plots of 500 m2 were established in the direction of the local topography (edaphic and hydrological gradient). For herbaceous sampling, 10 subplots of 1 m2 each were made, inside a randomly selected 500 m2 plot. For the soil, composite samples were made in 9 plots that were sent for analysis at the Soil Laboratory of EMBRAPA Amapá. The individuals in the plots were identified and the diameter at ground height (DAS) ≥ 3 cm of the woody individuals was measured. The families Fabaceae, Melastomataceae and Rubiaceae were the most representative among woody and herbaceous species. Byrsonima crassifolia (L.) Kunth (muruci) showed the highest relative frequency (47.37%), highest relative density (81.13%) and highest relative dominance (76.54%) among woody individuals. Among the herbaceous Tibouchina aspera Aubl. and Desmodium sp. presented higher relative frequency (FR), and Tibouchina aspera Aubl. higher relative density (RD). Woody and herbaceous plants have low diversity in the rupestrian savanna of RESEX Cajari. Despite this, the herbaceous community had greater diversity and evenness than the woody community. The topographic gradient promoted a variation in edaphic characteristics in the rupestrian savannah, which influenced the similarity between plots of woody and herbaceous species: higher and drier portion characterized by acidic soil, higher content of organic matter and macronutrients, which enhances plant growth in rocky environment when combined with adaptations in the roots for nutrient absorption; intermediate and lower humid portion presented more sandy and humid soil. Despite the scarcity of studies, which made comparisons difficult, this study provides relevant information that can guide further investigations. In this way, the need for further studies in the rupestrian savanna is evident, due to its ecological potential.