Eastern deciduous forests are threatened by habitat loss and fragmentation due to urban expansion from increasing city populations. Forests are important because they contribute to the preservation of native species and habitat, carbon sequestration, and atmospheric cooling. Increased urbanization and presence of nonnative plant species change the composition of ecological communities and alter forest function. The family Carabidae, ground beetles, are used around the world as ‘indicator taxa’ for monitoring forest health. Carabids are ecologically and taxonomically varied, abundant, and sensitive to human-caused disturbances. We studied communities of carabid beetles in rural, suburban, and urban forest fragments in Raleigh, North Carolina and Newark, Delaware. We tested the hypothesis that nonnative vegetation in urbanized forests will have an effect on carabid community composition. We quantified vegetation and carabid beetle communities in 12 forest fragments in each city. Forest fragments spanned a rural to urban gradient and a size gradient of 1 to 25 hectares. We collected carabid beetles every six weeks from May to December using pitfall traps. From a total of 239 pitfall traps, we collected 995 adult carabids. Carabid beetles were identified to species and categorized by life history traits, and pooled by forest fragment.
Results/Conclusions
Older forest fragments with established canopies were less colonized by nonnative plant species. We collected more carabids in forest fragments with less nonnative plant species and more coarse woody debris, and these sites had more predatory carabid species. Smaller and younger forest fragments had more nonnative plant species, and more generalist carabid species. Forest fragments with more nonnative plant species had less leaf litter, less soil organic matter, and less coarse woody debris. Forest fragments with more nonnative vegetation had less habitat for forest specialist carabid species. These results indicate that the community of plant species, specifically the presence of nonnative plant species, in urban forest fragments affect carabid community composition. This study is important because it quantifies the relationship between nonnative species and their effect on native ecosystems. These findings support the idea that improving remnant native habitats in urban areas, by removing nonnative species, may help to conserve forest-specialist carabid and other native biotic communities.