COMMUNITY COMPOSITION AND SOIL PROPERTIES IN NORTHERN BOLIVIAN SAVANNA VEGETATION

Abstract. Direct gradient analysis (Canonical Correspondence Analysis) of northern Bolivian savanna vegetation revealed correlations between the composition of plant communities and physical and chemical soil properties. Cover/abundance values for 193 species from 27 sites were related to data on eight soil factors. A water‐regime variable and the percentage of sand and silt were correlated with the first axis of the species‐environment biplot and explained most of the variation in community composition. Along this axis, species and sites of flood‐plain vegetation were separated from sites not affected by flooding rivers. The second axis of the biplot was correlated with soil‐chemical variables, namely extract‐able phosphate, base saturation, organic carbon, pH, and effective cation exchange capacity. Part of the variation in community composition can be explained by these soil nutrient variables. Grassland communities were separated from woody vegetation along the soil nutrient gradient, and floodplain communities of white‐water rivers from those of clear‐water rivers. The results of the gradient analysis indicate that the soil texture‐moisture gradient is the prime factor determining the variation in the floristic composition of the savanna communities examined, and that, in addition, the soil nutrient gradient accounts for some of the variation. 1990 IAVS ‐ the International Association of Vegetation Science