A Phytosociological Analysis of Species‐Rich Tropical Forest on Barro Colorado Island, Panama

Data on tree species composition and population structure are used as a source of ecological information on the species—rich forest of Barro Colorado Island, Panama Canal Zone (BCI). Thirteen stands, representing both the young and old forest on the Island, were sampled using 10 m ° 20 m quadrats for all individuals °2.5 cm dbh. Over 300 species were encountered and most were identified. The data are evaluated for interpreting late secondary succession (>60 yr), detecting soil—vegetation patterns, and for yielding autecological information. Successional status was estimated by placing species with similar population structure patterns into groups, and then calculating the abundance of species groups that seemed indicative of successional status. Five population structure patterns were recognized. The results suggest that the older BCI forest is not climax after at least 130 yr of succession. Both principal components analysis and a Bray—Curtis type ordination were used to determine whether ecological patterns on BCI are reflected by species composition. Forest age was best reflected by an ordination of the larger tree species. Species found only in the young forest or only in the older forest are identified. Stands with a distinctive gley soil were not segregated on the ordination. Species diversity increases most rapidly during the first 15 yr of succession, but continues to increase slowly after 65 yr. The Shannon—Wiener diversity measure averaged 4.8 (log base 2). Some data suggest that wind—caused canopy gaps are important for the persistence of several species in the older forest, e.g., Cecropia sp.