IMPLICATIONS OF FOLIAR MONOTERPENOID VARIATION AMONG ONTOGENIC STAGESOF THE CALIFORNIA BAY TREE (UMBELLULARIA-CALIFORNICA) FOR DEER HERBIVORY

As part of a larger detailed investigation of foliar monoterpenoid var iation in Umbellularia californica, monoterpenoid content was measured from trees at several sites in three ontogenetic stages: seedlings (< 30 cm), saplings (between 1 and 2 m) and adult trees (>4 m). Mature le aves were used in this study to standardize against the changes that o ccur during leaf development. Furthermore, as shown in other studies n ew growth of all three ontogenetic stages had extremely low terpenoid total yields (mg all monoterpenoids/g leaf dry weight). Variation due to collecting site, selected across a variety of community types and e nvironments, was not significant for any of the variables studied. How ever, monoterpenoid total yields varied significantly (P < 0.001) amon g ontogenetic stages: seedlings had less than half the yields found in the sapling and adult tree foliage, whereas total yields between sapl ing and adult tree foliage did not differ statistically. No significan t difference occurred among the ontogenetic stages in the ratios of hy drocarbons to oxygenated monoterpenoids. Little variation in monoterpe noid composition (% of the total yield by individual monoterpenoids) o ccurred among the ontogenetic stages. A year-long field study of Black tailed Deer browse intensity revealed no strong preference among tagge d shoots of mature leaves among ontogenetic stages with differing tota l yields. These results are discussed in relation to suggestions regar ding plant chemical defense against mammalian herbivory.