HOW TREE SPECIES DIFFER AS RECRUITMENT FOCI IN A TROPICAL PASTURE

Abstract

In a Neotropical pasture, I predicted that two characteristics of trees, type of fruit produced and amount of shade cast, would affect recruitment and growth of woody plants underneath them. I also predicted that woody plants that persisted in active pasture would affect the species assemblages under trees after pasture abandonment. To investigate these hypotheses, I examined the assemblages of recruits under several types of trees in active pasture and also under similar trees that were fenced off (enclosed) to simulate abandoned pasture. The trees were Ficus spp. (fleshy fruits, deep shade), Pentaclethra macroloba (dry fruits, deep shade), Cecropia spp. (fleshy fruits, sparse shade), and Cordia alliodora (dry fruits, sparse shade). Recruitment into “open” pasture plots (i.e., without trees) was also examined. In active pasture, the species assemblage of woody recruits depended on the tree under which they grew. The assemblage under Ficus was dense and diverse, under Cecropia and Cordia it was moderately dense and diverse, in open pasture it was sparse and species-poor, and under Pentaclethra it was dominated by its own seedlings. These patterns were found in the enclosed pasture as well, apparently because woody plants that had survived in the active pasture continued to grow after “abandonment.” However, after enclosure, many new plants also became established, such that the enclosed pasture plots had almost twice as many woody plants and species as the active pasture plots. Growth of woody plants was most rapid under trees with the least shade (Cecropia, Cordia) and in open pasture. In contrast, growth of recruits was slower under the much shadier Ficus, and thus, in the initial stages of succession, Ficus appeared not to be as important a “recruitment focus” for woody plants. Growth of recruits under the equally shady Pentaclethra was also slow, but Pentaclethra seedlings readily established just outside the canopies of parent trees, where they grew quickly and created dense, monospecific stands. The results of this study suggest that patterns of early succession to forest after pasture abandonment will depend on the kinds of trees found in the pasture. Persistent woody recruits under trees in active pasture constitute sources of advanced regeneration that will substantially affect forest succession after pasture abandonment.