-diversity as influenced by slope aspect and elevation in a seasonally dry tropical forest community in southern Mexico.
Gallardo-Cruz, José*,1, Meave, Jorge1, Pérez-García, Eduardo1, 1 Departamento de Ecología y Recursos Naturales, México, D.F., México
ABSTRACT- Many studies on tropical forests have focused on trends in vegetational attributes (composition, structure, and diversity) along various types of ecological gradients, mainly latitudinal, successional, rainfall and edaphic. However, at the landscape level the role of topography as an axis of floristic differentiation has not been fully explored, particularly regarding tropical plant communities. In this study we examined the effects of two major topographical factors (aspect and elevation) on the spatial floristic differentiation of a seasonally dry tropical forest established on a medium-size mountain (Cerro Verde, ca. 500 m elevation), located in the Nizanda region (Isthmus of Tehuantepec, S Mexico). We used 30 100-m2 plots to gather structural and floristic information for all plants > 30 cm in height; plots were sistematically placed in three altitudinal belts (low, mid and high), and on the south- and north-facing slopes of the mountain. The floristic survey rendered a total of 194 species. Analysis of structural variables (density, basal area, and cover) did not show a significant variation (two way ANOVAs, P > 0.05) between elevational belts or contrasting slopes. However, a numerical plot classification showed that in terms of floristic composition, samples located at different elevations did vary markedly. We conclude that in a seasonally tropical dry forest landscape an elevational gradient as small as 400 m may be associated to a significant -diversity, and that such floristic differentiation occurs regardless of the structural homogeneity.
Key words: topography, floristic differentiation, vegetation structure, plant diversity
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