Seed dispersal, gap dynamics and tree recruitment: the case of Cecropia obtusifolia at Los Tuxtlas, Mexico

Abstract

Abstract. We review data on the relationship be- tween seed dispersal of trees and treefall gap dy- namics at the population and community levels in tropical rain forests. We recognize two general dispersal syndromes: (1) pioneer (shade-intol- erant) and (2) persistent (shade-tolerant). The spa- tially (and temporally) wide seed dispersal syn- drome of pioneer trees is associated with recruit- ment in large gaps (>100 m?), which are infrequent in time and space. In neotropical forests these gaps occur at a rate of one every 1.8-2.8 yrs per hectare The spatially restricted seed dispersal of persistent (both understory and upper-canopy) trees is associ ated with recruitment in gaps >20m, which are about seven times more frequent than large gaps in moist or wet tropical forests. The uneven distribu- tion of treefall gaps in time and space results in the production of waves of recruitment in tree popula- tions. At Los Tuxtlas, Mexico, the treefall regime produces forest patches of 'recurrent perturba- tions' in which recruitment is an on-going process and 'stable sites' in which recruitment rates are low. Along with animal-mediated seed dispersal, rainfall-induced treefall patterns within and be- tween years may be controlling, in part, the popu- lation sizes of plants.