Ecological change by alien plants in an urban landscape

Habitat destruction and alien species invasions are leading causes of worldwide species loss. Alien plant species are well known to disrupt the ecological services of native ecosystems, change the composition of native habitats, and cause declines in the populations of native flora and fauna. This dissertation examines the patterns and impacts of alien species invasions in the New York metropolitan region, a major urban region. I begin this dissertation with a comprehensive life history analysis of the woody species of the New York metropolitan region to determine the life history traits that enable a species to be successful in the urban landscape. Alien species that are deciduous trees, shrubs and vines with fleshy fruits are the most successful. I then use landuse/landcover data of the State of New Jersey to determine the relationship between landscape patterns of urbanization and alien species distributions. Urbanization promotes the replacement of native species with alien species. This increase of alien species with increasing urban land cover also promotes biotic homogenization of the flora. The rest of this dissertation examines local scale patterns and the impacts of alien plant invasions. Using data collected for the past 50 years at the Hutcheson Memorial Forest, a 26 ha old growth forest in central, suburban New Jersey, I examine the changes in the plant community, the introduction of alien plant species and the consequences of these invasions over time. Changes in the old growth forest vegetation over the past 50 years show the loss of native species and gain of alien invasive species. In 2003, alien and native species richness were positively correlated, indicating the old growth does not exhibit biotic resistance to invasions. Finally, I experimentally test the effects of Microstegium vimineum , an alien invasive grass, and deer herbivory on forest understory herbaceous diversity and canopy tree regeneration, using removal experiments and addition of tree seedlings. Microstegium vimineum inhibits the survival and growth of canopy tree seedlings. Understanding the patterns of alien species spread and the consequences of these invasions are critical for the restoration and management of remnant urban habitats.