Diversity and horizontal structure in the tropical forests of the Osa Biological Corridor, Costa Rica

Abstract

Were established 14 permanent plots (50 m x 100 m) distributed in different forests of the Osa Biological Corridor (CBO), Costa Rica. We evaluated the diversity and horizontal structure in four successional stages of forest ages: 5 to 15 years, 15 to 30 years, more than 30 years and primary. All trees with d ≥ 5 cm were botanically identified and their diameter (d) were determined. The results indicated that secondary forests were less diverse and were less mixed than the primary for the different indices used; but its value increased with forest age. The species accumulation curves based on the area and number of individuals sampled, showed that the richness and diversity increases proportionally with age of forests. Basal area and number of species are listed as best parameters to measure the degree of forest recovery, contrary to the number of trees per hectare which is not as effective. The distribution of species and number of trees by diameter class took the form of inverted J, where the reserve of trees and species in the first classes ensure the balance of forests. The main difference in the distribution of basal area by diameter class is given in the last classes (> 55 cm), where forests had the highest values, which are concentrated in a few species and large trees.