Introduction:

Relief has a significant influence on the spatial distribution and heterogeneity of arboreal vegetation in tropical forests.

Objective:

Tree structure and diversity were analyzed in three reliefs on the Oaxaca coast: plain, premountain and low mountain.

Materials and methods:

Three 1,000 m2 randomly selected sampling units were established in each relief to record total height, canopy cover and diameter at breast height (DBH) in three size classes: poles (Po), saplings (Sa) and seedlings (Se). The structure was characterized by vertical stratification, diameter distribution, Importance Value Index (IVI) and Forestry Value Index (FVI). The diversity was estimated with the Shannon-Wiener Index (H') and floristic similarity with the Sorensen Index (SI).

Results and discussion:

The species with the highest IVI and FVI were: Bravaisia integerrima (poles) and Pithecellobium dulce (saplings and seedlings) in premountain; Cecropia obtusifolia and Swartzia cubensis (poles), Cupania dentata (saplings) and Nectandra globosa (seedlings) in low mountain. The diversity (H') was significantly (p < 0.05) higher in low mountain (3.24) than in premountain (1.76) and plain (2.07). Floristic similarity (SI) of poles and saplings was lower between plain and premountain, and for seedlings it was lower between plain and low mountain.

Conclusion:

Species richness and diversity were different in each size class in at least one relief.