Abstract
Observations were made on growth, mortality and phenology of two mangrove populations on the Pacific coast of Costa Rica. Major phenological events were closely related to the water balance of the study site. Fruits developed and fell only when soil water recharge was completed. Growth and mortality of Avicennia bicolor and Rhizophora harrisonii plants were compared between monospecific and mixed stands. Avicennia bicolor grew better in the monospecific stand and seemed to be outcompeted in the mixed stand where R. harrisonii dominates the canopy. While propagule dispersal might be considered primarily responsible for seedling distribution, differences in responses to environment reflected in survival and growth rates seem to be the best explanation for plant distribution within a mangrove forest.