STUDIES IN MONODOMINANT FORESTS IN EASTERN MATO GROSSO, BRAZIL: II. A FOREST IN THE AREÕES XAVANTE INDIAN RESERVE

Abstract

The floristic composition, structure, soil fertility and leaf nutrient concentrations were analysed in a monodominant forest of Brosimum rubescens Taub. located in the Areões Xavante Indigenous Reserve (14°34′S, 51°58′W). The area lies in the ecotone between Amazonian forest and cerrado in the municipality of Água Boa, Mato Grosso State, Brazil. Sixty nested plots (10 × 10m each) were located in a representative portion of the forest, giving a total sampling area of 0.6ha (40 × 150m). A total of 609 trees ≥ 5cm dbh belonging to 57 species, 46 genera and 32 families were present. The most important family was Moraceae, with B. rubescens as the dominant species with a relative dominance of 59%. The diameter distribution of B. rubescens was unbalanced, indicating an episodic recruitment that could lead to future changes in the forest structure. The high basal area per hectare of B. rubescens indicates the possibility of sustainable logging for commercial exploitation. Analysis of composite soil samples collected from the surface layer (0–10cm) of each of the 60 plots did not indicate any significant gradients in fertility within the area sampled. Mean soil pH was 4.6 and the availability of essential nutrients was very low (0.22cmol(+) kg⁻¹ K, 0.048cmol(+) kg⁻¹ Ca, 0.167cmol(+) kg⁻¹ Mg, and 1.5mg kg⁻¹ P). The higher availability of Mg in the soils in comparison with Ca was a feature observed in other monodominant forests in the Amazon region, as well as in other parts of the world. Analysis of foliar samples showed that the dominant species, B. rubescens, maintained higher foliar concentrations of K, Ca and Mg than other species in the forest. This probably indicates a competitive advantage for this species. Also, the higher concentrations of Mg in the soil did not affect its uptake of Ca or K.