Soil chemical properties under individual evergreen and deciduous trees in a protected Venezuelan savanna.
A study of soil chemical properties was made under the three most common evergreen tree species (Curatella americana, Byrsonima crassifolia, Bowdichia virgilioides) and two common deciduous tree species (Godmania macrocarpa, Cochlospermum vitifolium) growing in a seasonal savanna at Calabozo, Venezuela. The site has been protected from fire and cattle grazing since 1961. The objectives were: (i) to test the hypothesis that accumulation of soil organic matter (SOM) and K in the mata (forest)/grassland ecotones were due to the predominance of evergreen species in those ecotones, and (ii) to get data on the chemical properties of soils under individual trees of the most relevant species. It was found that the species studied (with the exception of C. vitifolium) induced a statistically significant accumulation of SOM, which in turn allowed a build up of soil exchangeable Ca, Mg, and K in soils under trees, compared with soils under grasses. The lack of soil N accumulation and soil exchangeable acidity (Al + H) neutralization under individual trees (compared with results in previous work under mata soils), was attributed to the shorter time required for an individual tree to grow, compared with mata soils. The soils under evergreen species showed higher SOM, effective cation exchange capacity, and exchangeable K than those under deciduous ones. These results were attributed to the slower decomposition rates of evergreen species' plant tissues as well as to a more efficient humification process under those savanna trees. These last results were consistent with the hypothesis that evergreen fire-resistant species, more abundant in the mata's ecotones, are responsible for the higher SOM and exchangeable K found in them (relative to the mata, where deciduous species predominate).