PHYSIOLOGICAL CONSTRAINTS ON RESPONSE BY OSTRYA-VIRGINIANA (BETULACEAE) TO LOCALIZED FOLIVORY

Individual twigs of eastern hophornbeam were experimentally defoliated at the time of spring peak herbivore abundance for this plant species. When all three leaves directly subtending developing fruits and all leaves (three to five total) from the nearest twig were removed to simulate natural folivory, there was a 25% decrease in mass of individual fruits (but not in fruit number) compared with control twigs. Lower damage of up to 50% area removal for subtending and nonsubtending leaves combined produced no significant decrease in reproductive output. Experimental defoliation had no effect on growth, reproduction, or survivorship of treatment twigs in the subsequent year. At no time during the study was natural herbivore damage high enough on individual twigs to decrease their reproductive output. These results add to the evidence that resource movement among adjacent twigs and branches of woody plants is not sufficient to compensate for localized damage. Thus, we must consider both the pattern of folivory as well as total leaf area removed to understand the effects of folivorous insects on plant growth and reproduction.