The establishment of tree plantations on degraded lands can facilitate the regeneration of native species that could not otherwise grow in open micro sites or in competition by herbaceous species. The present research investigated tree regeneration under mixed and pure plantations of native species at La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. The highest abundance of regenerating tree individuals was found in the understory of the mixed plantation (composed of Hieronyma alchorneoides + Vochysia ferruginea + Balizia elegans + Genipa americana) with 10, 156 individuals/ha, followed by pure plantation of H. alchorneoides with 7891, V ferruginea with 5703, B. elegans with 4219, G. americana with 1484, and the natural regeneration control with 703 individuals/ha. The highest mean number of species was found in the understory of the mixed plantation (11 species in 32 m(2)), followed by pure plantation of V ferruginea (8.0), H. alchorneoides (7.0), B. elegans (5.0), G. americana (3.0) and control (1.0). Melastomataceae was the most abundant family in the understory of the mixed plantation and in the pure plantation of V ferruginea, while Rubiaceac was the most abundant under H. alchorneoides. In constrast, Piperaceae was the most abundant family under pure plantations of G. americana and B. elegans. In addition, species of primary forest of the region were found in the understory of the mixed plantation and under the pure plantations of H. alchorneoides and V. ferruginea. These are promising indicators for the use of these plantations as accelerators of natural forest succession in the region. Very few woody species were found in the control, natural regeneration plots. Factors that may impede the establishment of woody species in the control may be the lack of perches for seed dipersers and invasion by herbaceous vegetation which outcompetes the tree seedlings in their growth. (C) 2002 Elsevier Science B.V. All rights reserved.
