Effect of shrubs on tree seedling establishment in an abandoned tropical pasture


Karen D. Holl, Department of Environmental Studies, University of California, Santa Cruz, CA 95064, USA (tel. +831-459-3668; fax +831-459-4015; e-mail kholl@cats.ucsc.edu).


  • 1The objective of this study was to evaluate whether early successional shrubs facilitate, tolerate or inhibit different stages of tree establishment in abandoned tropical pasture.
  • 2Seed rain, seed predation, seed germination and seedling survival of tropical forest trees in pasture grass, below small (< 25 m2) shrub patches and below large (> 40 m2) shrub patches, were compared in one abandoned pasture in Costa Rica over 2 years.
  • 3Seed rain of animal-dispersed trees was higher below both large and small shrub patches than below grass. Seed rain of wind-dispersed trees did not differ in the three patch types.
  • 4Predation of all animal-dispersed seeds combined and of three individual species was significantly higher below large and small shrub patches compared with below grass; predation of five species did not differ significantly in the three patch types.
  • 5Germination did not differ significantly in the three patch types for any of the species.
  • 6Seedling survival was highest below large shrub patches for three of four species.
  • 7Computer simulations of probabilities of seeds arriving in the pasture and surviving to the seedling stage suggest that early successional shrubs have a net facilitative effect on the early stages of forest tree seedling establishment compared with areas without shrubs in the pasture studied, although variance was high. Shrubs may facilitate, inhibit and tolerate different stages of tree seedling establishment.