| Invasive plants have potential to impact seriously native plants and vertebrates because they compete with native plants and provide food and habitat for native vertebrates. My study focuses on invasive plant effects on native plants and native vertebrates. I reviewed and analyzed results of invasive plant-native vertebrate interaction studies with a meta-analysis and found that degree and type of effect vary depending on species and ecosystem/community involved. I studied impacts of two invasive plants, Phragmites australis and Lythrum salicaria, on species composition and abundance of native plants, small mammals and birds in six Hudson River freshwater tidal wetlands. Using a complete randomized block design, I set up three plots in each wetland, one in each of three dominant vegetation types: L. salicaria, P. australis and Typha angustifolia/Typha latifolia. T. angustifolia/T. latifolia served as the control. I surveyed native plants, small mammals, birds and arthropods in each plot. I also set up artificial nests in each plot to assess predator access. I analyzed data using analysis of variance, multi-dimensional scaling, analysis of similarity, BIOENV, canonical correspondence analysis and Poisson/negative binomial regression. Native plant species composition and abundance differed significantly between Phragmites dominated plots and plots dominated by the other species. Invasive plant species characteristics and zonation determined differences in native plant species composition and abundance. Native small mammal species composition and abundance differed significantly among wetlands across years. Native bird composition and abundance differed significantly among wetlands, months and years. Different wetland characteristics and land use in areas surrounding each wetland determined which small mammal and bird species could utilize each area. Within different small mammal species (Peromyscus leucopus, Microtus pennsylvanicus, and Zapus hudsonius), body condition (weight/length) only differed among wetlands. Arthropod order abundance and nest predation also differed among wetlands. Differences in body condition were attributed to differences in resource availability among sites. Differences in arthropod abundance and nest predation were attributed to differences in percent area of land use types and, in the case of nest predation, in small mammal abundances among wetlands. It is possible that wetland effects overshadowed invasive plant effects therefore further research is recommended. |
