POSTDISPERSAL SEED AND SEEDLING MORTALITY OF TROPICAL DRY FOREST TREES AFTER SHIFTING AGRICULTURE, CHIAPAS, MEXICO

Vertebrate attack accounted for 98.4% of all seed loss during the two months following dispersal. This accounted for, across all habitat typ es, 94% of Bursera, 76% of Spondias, 37% of Swietenia and 25% of Eryth rina seeds artificially dispersed. Bursera, Spondias and Swietenia see ds in early successional habitat suffered significantly greater predat ion than in either older abandoned (30 y) or mature forest plots. Eryt hrina showed generally low loss to predation in all plots. Seeds attac ked were more often removed from, rather than buried or eaten at, the dispersal site. In young secondary habitats, however, seeds of Bursera and Spondias were more frequently eaten at the site. Seeds dispersed individually rather than in larger aggregations (5, 10) were more like ly to survive in mature forest and late secondary habitat. This advant age was lost in Bursera and Swietenia when they were dispersed to youn ger successional habitats. At the early seedling stage, recruitment of Bursera and Swietenia was highest in the older secondary habitats. Se edlings of Erythrina showed the lowest overall losses to any of the mo rtality factors identified during the first two months of establishmen t. Seeds of forest tree species arriving in secondary habitat were mor e vulnerable to attack by non-flying vertebrates than in mature forest . Survival of seedlings of these species was most closely related to t he moisture-conserving status of the habitat.