Barriers to Forest Regeneration in an Abandoned Pasture in Puerto Rico

J.K. ZIMMERMAN, J. B. PASCARELLA, T. M. AIDE

ABSTRACT: Sources of forest regeneration (soil seed bank, seed rain) and barriers to seedling establishment were examined in a recently abandoned pasture in eastern Puerto Rico. Few woody species were jfound in the soil seed bank or in the seed rain. The number of seeds and species in the seed rain and soil seed bank declined with distance from the adjacent secondary forest. Nine species naturally dispersed and colonized plots during the study, with the wind-dispersed tree Tabebuia heterophylla being the predominant colonizer (91 % of all seedlings). Barriers to seedlings establishment were determined using a blocked field experiment with eleven woody species representative of a variety of life histories. Each species was planted under the pasture vegetation (control) or in areas where all vegetation was removed (removal). Germination was enhanced for four species in the control treatment, five species were not affected, and two species did not germinate under either treatment. Survival to 6 months was higher in the removal treatment for two species. Seedling biomass was greater in the removal treatment at 12 months for one species. Seed mass was a good predictor of germination success and final shoot biomass, but not survival. This stufy demonstrates that seedling recently abandoned pastures with a mix of known pionner species may accelerate the rate of secondary succession, but some species will have to be planted in laterb succesional stages in order to overcome strong barriers to establishment.

Keywords: germination, pasture, Puerto Rico, regeneration, seed bank, seed rain, Tabebuis