EFFECTS OF DEFOLIATION ON ERYTHROXYLUM HAVANENSE, A TROPICAL PROLEPTIC SPECIES

Proleptic flowering is common among plant species from tropical season al forests. In these species flower initiation and anthesis are separa ted by a prolonged rest period (the unfavorable season), and the two p rocesses are controlled separately. Proleptic species are appropriate for assessing the within- and between-season effects of herbivory on f lowering and reproductive success. We investigated the reproductive co nsequences of artificial defoliation of the proleptic shrub Erythroxyl um havanense, in a seasonal dry forest in western Mexico. Twenty indiv iduals in each of three sites were randomly assigned to one of four tr eatments: control (no manipulation), and three levels of leaf area rem oved: 0, 25, and 100%. Plants in the latter three treatments were spra yed with insecticide to prevent additional foliage consumption by natu ral herbivores. Within a season undamaged plants (control and 0% defol iation) produced from two to four times more seeds than damaged ones ( 25 and 100% defoliation). In addition, completely defoliated plants ex hibited a significant increase in both fruit maturation time (8 d) and average seed mass (9.5%), when compared to the plants in the other tr eatments. There was no evidence of a trade-off between seed number and seed mass, or between ripening time and seed mass. One year after def oliation, vegetative growth (basal area increment) was reduced only by 100% defoliation. Likewise, flower and fruit production were signific antly reduced only in this treatment. Although defoliation reduced see d production in both years, only the first year's reduction was a dire ct consequence of defoliation. Seed production decline in year 2 was a n indirect effect of the reduction in flower number, suggesting that f ruit and seed maturation do not depend on resources stored, but on ann ual production of photosynthates. Plant survival was not affected up t o 5 yr after defoliation. Since most of the effects were evident only in the 100% defoliated plants, our results reflect those instances whe n insect outbreaks occur and E. havanense plants are completely defoli ated.