Response of tree diversity and community composition to forest use intensity along a tropical elevational gradient

Abstract

Question: Land-use change and intensification are currently the most pervasive threats to tropical biodiversity. Yet, their effects on biodiversity change with eleva-tion are unknown. Here, we examine how tree diversity and community composition vary with elevation and how the effects of forest use intensity on tree diversity and community composition change within elevations.Location: Eastern slopes of the Cofre de Perote mountain, state of Veracruz, Mexico.Methods: We assessed tree diversity and composition using a sampling design in which elevation was crossed with three levels of forest use intensity: old-growth, degraded, and secondary forests. We established 120 20 m × 20 m forest plots, lo-cated at eight sites between 0 m and 3,545 m. At each site, five replicate plots were inventoried for each level of forest use intensity.Results: Our analyses revealed an interactive effect between elevation and forest use intensity affecting tree diversity and community composition along the eleva-tional gradient. Contrasting effects of forest use intensity within elevation resulted in tree diversity following a low-plateau pattern for old-growth and a bimodal pat-tern for degraded and secondary forests. Along the entire elevational gradient, there were 217 tree species distributed within 154 genera and 80 families. Species accu-mulation curves revealed that forests at 0 m and 1,500 m elevation showed differ-ences in species richness among forest use intensities. In contrast, species richness did not differ between old-growth forest and the other forest use intensities in five of the eight studied elevations. In terms of community composition, secondary forests differed from old-growth and degraded forests.Conclusion: Our results suggest that the interactive effects of elevation and for-est use intensity change tree diversity patterns and community composition along a tropical elevational gradient. Degraded forests were similar to old-growth forests in terms of species diversity and composition, suggesting that they may act as a safe-guard of tree diversity in human-dominated tropical landscapes.