For ESA Annual Meeting 1999:
MORRISON*, JANET A. AND LEONE BROWN. The College of New Jersey, Ewing, NJ, 08628, USA. Herbivore exclosure effects on the forest herb layer and an invasive plant, Alliaria petiolata.
One reason suggested for why some non-native plants invade is because of little or no herbivory. The biennial Alliaria petiolata is a serious invader of fragmented deciduous forests. We investigated the effect of caging Alliaria-dominated plant communities in 2m2 plots to prevent herbivory by deer and other large herbivores, in three different forests (two in the suburbs with deer, one in New York City without deer). We measured stem heights on second-year Alliaria; caged plants were significantly larger compared to uncaged plants in one suburban forest, Mt. Holly Preserve, but not in the other forests. Mt. Holly also had lower vegetation cover in the herb layer and frequent sightings of deer, suggesting more browsing in general. In the suburban forests, Alliaria cover was lower outside cages, but caging did not affect the sum of other speciesí cover. We also observed growth patterns of Alliaria consistent with deer browse (shredded stems and regrowth from lateral meristems). We conclude that herbivores do eat Alliaria, probably when other foods are scarce, but have had little effect on abundance of the remaining plant community after almost two years of caging. Alliaria petiolata appears able to invade a forest in spite of browsing by herbivores.