The occurrence and diversity of tree legumes as influenced by soil properties in selected tropical forests in Costa Rica

Abstract

Legumes play important roles in tropical forests due to their contribution to N₂-fixation and nutrient cycling. Our objectives were to determine which soil properties, if any, affect the occurrence and distribution of tree legumes in a tropical wet and a tropical dry forest in Costa Rica, to make small-scale inventories of the legume populations of these same forests and to study the soil ameliorative effects of legumes and non-legumes. Tree and soil surveys were undertaken in both forests for these purposes. Soil properties found to influence legume occurrence in the dry forest were texture and exchangeable Mg content. Exchangeable K, Ca and available P were influential on the occurrence of members of the Leguminosae subfamilies. In the wet forest, soil properties found to influence legume occurrence were levels of available P and exchangeable Al. In addition to these, other variables such as texture and exchangeable Ca and Mg were influential on the occurrence of the legume Pentaclethra macroloba, a very abundant species in this forest. Based on the Shannon index of diversity, legume species were most diverse in the dry forest followed by the ultisol soil and inceptisol soil sites in the wet forest. Differences in the soil under legumes and non-legumes in the dry tropical forest include levels of exchangeable Ca, soil pH and total Mo.