Effects of Defoliation on Erythroxylum Havanese, a Tropical Proleptic Species

Proleptic flowering is common among plant species from tropical seasonal forests. In these species flower initiation and anthesis are separated by a prolonged rest period (the unfavorable season), and the two processes are controlled separately. Proleptic species are appropriate for assessing the within— and between—season) effects of herbivory on flowering and reproductive success. We investigated the reproductive consequences of artificial defoliation of the proleptic shrub Erythroxylum havanense, in a seasonal dry forest in western Mexico. Twenty individuals in each of three sites were randomly assigned to one of four treatments: control (no manipulation), and three levels of leaf area removed: 0, 25, and 100%. Plants in the latter three treatments were sprayed with insecticide to prevent additional foliage consumption by natural herbivores. Within a season undamaged plants (control and 0% defoliation) produced from two to four times more seeds than damaged ones (12 and 100% defoliation). In addition, completely defoliated plants exhibited a significant increase in both fruit maturation time (8 d) and average seed mass (9.5%), when compared to the plants in the other treatments. There was no evidence of a trade—off between seed number and seed mass, or between ripening time and seed mass. One year after defoliation, vegetative growth (basal area increment) was reduced only by 100% defoliation. Likewise, flower and fruit production were significantly reduced only in this treatment. Although defoliation reduced seed production in both years, only the first year's reduction was a direct consequence of defoliation. Seed production decline in year 2 was an indirect effect of the reduction in flower number, suggesting that fruit and seed maturation do not depend on resources stored, but on annual production of photosynthates. Plant survival was not affected up to 5 yr after defoliation. Since most of the effects were evident only in the 100% defoliated plants, our results reflect those instances when insect outbreaks occur and E. havanese plants are completely defoliated.