Composition, diversity and distribution of woody species in relation to vertical stratification of a tropical wet evergreen forest in Bangladesh

The composition, diversity and spatial distribution pattern of woody species were analyzed along the vertical profile of a tropical wet evergreen forest in Bangladesh. The forest stand consisted of five vertical strata. The species composition was moderately similar among the strata, while the highest degree of similarity was between fourth and bottom strata. Bursera serrata Wall. ex Colebr. was the most dominant species, and may be typically climax species together with Microcos paniculata L. ex W & A. and Maesa ramentaca   (Roxb). A. DC in terms of their high importance values. Species–area relationships depict compositional instability of the present forest, because expected maximum numbers of species (165) were four times higher than the recorded numbers of species (40) for the total stand. Smaller species richness in the upper strata was compensated by greater species evenness (Pielou’s index J′J′ ), resulting in almost constant Shannon’s index H′H′ across the strata. It indicates each stratum may have the same role in maintaining high woody species diversity. The rate of equality of individuals among the different species decreased with increasing species richness due to decrease of J′J′ from the top stratum downward. The distribution pattern of the entire stand was greatly influenced by the aggregated distribution of the majority of the juveniles those mainly appeared in the bottom stratum. However, vertical strata shared a mixed distribution pattern of random and aggregate which followed from the upper strata to downward. This type of distribution pattern for stratified stand is probably consistent in tropical forests.