VARIABLE BUDBREAK AND INSECT FOLIVORY OF GAMBEL-OAK (QUERCUS-GAMBELII FAGACEAE)

Budbreak of individual ramets of clonal Gambel oak (Quercus gambelii: Fagaceae) was advanced experimentally to test the effects of altered timing of budbreak and hence, leaf age, on patterns of folivory. Early-season folivory by leaf-chewing insects was significantly greater on younger leaves of control ramets than older leaves of experimental ramets. However, differences in cumulative folivory between control and experimental ramets disappeared by the end of the growing season. Colonization by three species of late-season leafminers was also unaffected by altered budbreak, indicating the impact of altered budbreak on folivores is concentrated early in the growing season. Analyses of nutritional and allelochemical content of experimental and control ramets correspond to the patterns of folivory; leaves of experimental ramets were significantly higher in gallotannin content than leaves of control ramets, but these differences also waned by the middle of the growing season. Our results suggest that variable budbreak can alter degree of folivory on Gambel oak, but only early in the growing season. The evolutionary implications of, and constraints on, variation in budbreak in woody plants are discussed.