Influence of soil fertility on the distribution of tree species in a deciduous forest in the Triangulo Mineiro region of Brazil

Dry semideciduous and deciduous forests occur only on calcium-rich soils and occupy almost 20% of the 200 million ha of the cerrado region of central Brazil. Other savanna physiognomies of woodlands and grasslands, and gallery forests generally occur on acid soils with low calcium levels. The literature on phytosociological aspects of such cerrado physiognomies is quite abundant whereas there is very little information on deciduous forests. Also lacking is information on soil fertility and its influence on species distribution. The objective of the present study was to study the distribution of native species within a dry deciduous forest in the Araguari river valley, Uberlandia, Minas Gerais as related to soil properties. A 1-ha sampling area, with no apparent difference in physiognomy, was divided into fifty 10 m x 20 m plots arrayed in 10 x 5 grid and all trees with a minimum circumference of 15 cm at 1.30 m height were surveyed. A composite soil sample was collected from 0 to 10 cm depth in each plot and soil pH, organic C and nutrient availability were determined. Cluster analysis based on soil chemical properties showed the existence of two distinct groups of plots. Further field examinations revealed that the forest was situated in an area of transition between mica schist and basalt parent materials, without any apparent difference in the forest physiognomy. The basalt-derived soil in 23 plots had significantly higher availability of Ca (47.0 cmol(+) kg(-1) soil), Mg (2.59), and K (0.96) than the mica schist derived soil (Ca-18.4, Mg-1.29, and K-0.66) in the remaining 27 plots, though both soils would be classified as eutrophic. A total of 59 species belonging to 27 families were encountered in the area as a whole, of which 36 were common to both soils. In total, 16 species occurred exclusively on the mica schist soil and 7 on the basaltic soil. Myracrodruon urundeuva Allem. (Anacardiaceae) and Tabebuia roseo-alba (Ridl.) Sandwith (Bignoniaceae) were species with high importance values in the forest as a whole. Though there was no significant difference in the diversity index between the two soils, the importance values of these species was larger in the basalt-derived soil with higher nutrient availability.