The nature of savanna heterogeneity in the Orinoco Basin
1998
SAN JOSE, J. J. | MONTES, R. | MAZORRA, M.
Detrended Canonical Correspondence Analysis (DCCA) was used to describe the relationship between savanna environments and vegetation community composition in the Orinoco Basin. TWINSPAN derived three major types of savanna vegetation, each with its own floristic and physiognomic features. The first group reflected a plant association with species of Trachypogon occurring in moderately infertile soils with low water availability and high bulk density. This group is distributed mostly on hilltops and dissected plains of the northern Orinoco savannas. The second group has the highest species diversity in habitats occurring in the northern Orinoco with extremely infertile soils. The third group, on the other hand, has a considerable number of species belonging to the Leguminosae and Cyperaceae families and linked to the habitats of the eastern Colombian savannas with the highest soil water availability, a shorter dry season and higher precipitation. The regional analysis of the Orinoco savannas suggests edaphic controls to be important. Changes in the underlying geology have affected topography and soil formation, which results in variation in water and nutrient status. The moisture regime and hydrological features are acting as the major regional determinants, while nutrient levels and distinctive surface soil properties provide the subregional determinants. The local boundary, at any given site, is strongly determined by nutrient shortage and acidity. Also, biogeographic and floristic considerations were taken into account to explain differences in species composition.
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