Influence of Invasive Species on Coastal Plant Communities Throughout the world, biological invasions have become one of the most pressing environmental challenges faced by land managers. Not only must they reduce that chances that non-native species are introduced into protected lands, but they must also contain the spread of exotic species that are already present and restore lands that have been degraded by the spread of these taxa. Although most land managers contend with hundreds of exotic species, remarkably little is known about which invaders have large effects on communities and ecosystems. Thus, to address this issue, my graduate students and I are investigating the effects of non-native plant species on the communities they invade, and we are focusing on some of the most problematic exotic species and threatened habitats in California. a) Maria E. Alvarez and I have completed a project that explores the habitat-specific effects of Cape Ivy (Delairea odorata; Asteraceae) on coastal plant communities (publication). This perennial vine from South Africa has invaded extensive portions of the western U.S., and we have conducted both comparative and experimental studies to address its effects on three coastal plant communities in northern California. Our research clearly demonstrates that Cape Ivy dramatically reduces plant species richness and seedling recruitment in the areas it invades, regardless of habitat type. b) Karen A. Gaffney and I have completed a project that considers the influence of a highly invasive Asia grass, Giant Reed (Arundo donax), on riparian plant communities in northern California. This aggressive invader outcompetes native vegetation and, like many grasses, can increase fire intensity and frequency wherever it occurs. Our research has shown that invasion by giant reed significantly reduces perennial species richness (especially native woody species) and increases the abundance of Vinca major, another invasive perennial. Because native stream-side vegetation is vital for creating shaded habitats used by salmonids and other aquatic taxa, the transformation of riparian plant communities by giant reed is likely to have far-reaching effects on stream assemblages. c) Denise Cadman and I have completed an experimental study to assess the influence of litter accumulation from exotic grasses on the composition of plant communities associated with vernal pools. These imperiled seasonal wetland communities are of considerable interest to conservation biologists because of the diverse range of often endemic species that inhabit them. Large amounts of dead organic matter commonly accummulate in these pools due the invasion of non-native grasses from the surrounding grassland habitat. We have hypothesized that such organic biomass inhibits germination of native plant species, and last year initiated a factorial thatch-removal experiment to evaluate this possibility. Although we only have data for one year, they indicate that removal of accumulated plant litter in the autumn results in dramatically decreased cover of non-native grass species the following spring and, in many pools, increased cover of native species. If these patterns persist, removal of dead grass biomass may prove to be a simple yet effective means of restoring vernal pools that have been degraded by the invasion of exotic grasses.