Patterns in the vertical structure of the tropical lowland rain forest of Los Tuxtlas,Mexico

The vertical structure of one hectare of tropical rain forest was studied at Los Tuxtlas, State of Veracruz, Mexico. The structure was analysed at various scales of analysis, using different methodologies e.g. profile diagrams (0.1 ha) and vertical structure diagrams (1 ha). All profile diagrams suggested presence of stratification to some extent. However, simultaneous evaluation of several adjacent profile diagrams showed that the use of one profile diagram only can be very misleading: gaps or layers apparent in a diagram did usually not reflect gaps or layers that could be recognized in the field.Structure diagrams of abundance, basal area and crown cover showed that this forest community is not stratified, with the exception of an understorey layer below 7.5 m dominated by palms. The vertical structure was described using arbitrarily chosen height intervals. From the forest floor to the canopy top basal area, percentage of deciduous species (and individuals), and percentage of compound-leaved species (and individuals), increased, but total number of individuals and number of species decreased. Leaf sizes tended to decrease in the same direction, and crown cover was approximately evenly distributed. Species from different families dominated different parts along the vertical plane. It is concluded that the vertical structure of tropical rain forest can best be described as a complex gradient, involving many community features. Stratification can best be emphasized as a special case of such a gradient.