Forest Regeneration from Pasture in the Dry Tropics of Panama: Effects of Cattle, Exotic Grass, and Forested Riparia

We currently have the opportunity to restore one of the most threatened tropical ecosystems on the Pacific coast of Panama as a consequence of land use change. Factors that influence succession must be understood in order to capitalize on natural regeneration mechanisms. In this study, we determined the effects of exotic grass removal, cattle removal, proximity to forested riparian zones, and topography (upslope vs. downslope) on the initial stages of forest regeneration from pasture in a dry tropical region. After 3 years, basal area, stem density, and species richness of plants (trees, shrubs, vines, and herbs) were significantly and positively affected by exclusion of cattle, presence of exotic grass (no herbicide application), and presence of adjacent forested riparian zones (p < 0.01). Interactions between factors were not significant. Cattle foraged and stomped on vegetation, whereas herbicide application, although effectively removing grass, also killed tree and shrub sprouts, the major source of regrowth. Proximity to forested riparian zones had the greatest effect on species diversity. Shannon's index for diversity (H) equaled 3.23 in plots adjacent to forested riparian zones as compared to 2.78 in plots not associated with these areas. Our recommendations during the early stages of forest succession are to (1) exclude cattle, (2) make site-specific decisions about herbicide application based on the presence or absence of forested riparia and prevalence of coppicing, and (3) actively conserve and protect riparian zones, which function as a critical source of diverse propagules.