Soil Nutrients and Tree Species Richness in Costa Rican Forests

Analysis of published data for forty-six Costa Rican forest sites indicates a negative correlation between soil nutrient availability and tree species richness. P, K, Ca, Na, total bases, base saturation, and cation exchange capacity showed significant (P< 0.01) correlations, while available nitrogen, total nitro- gen, organic matter, Mn, and Mg were not significantly correlated wth species richness. With six measures of soil nutrients, a stepwise regression gave an R2 of 0.71. Correlations between species richness, precipitation, tree density, tree height, and soil fertility, are consistent with the interpretation that the highest species richness occurs under poor growth conditions. Results of field and glass- house fertilization experiments are reviewed.