EFFECTS OF RECENT LAND-USE PRACTICES ON SOIL NUTRIENTS AND SUCCESSION UNDER TROPICAL WET FOREST IN COSTA-RICA

The effects of a variety of agricultural land uses were studied using soil nutrients, forest structure, and species assemblages as indicators. We compared soil properties and successional forests between abandoned cacao (Theobroma cacao) and abandoned palm (Bactris gasipaes) orchards, abandoned pasture, and mature forest. These sites co-occupy an alhivial, terrace soil (Andic Dystropept) at La Selva Biological Station, Costa Rica. The agricultural sites were originally cleared of most or all forest vegetation approximately 30 years ago and went into succession approximately 7 years ago. Forest structure, species composition, soil nitrogen and phosphorus pools, and nitrogen-mineralization and nitrification rates were measured for each site. The abandoned palm orchard had lower basal area and stem density than other secondary forests of the same age. It also had significantly smaller nitrate (NaOH-extractable) and organic pbosphorus pools and significantly lower net rates of nitrogen-mineralization and nitrification. It is evident that preserving tree cover does not necessarily maintain soil fertility. We found species richness and diversity in the secondary forests to be positively, correlated with basal area at the time of abandonment.