Are native plants always better for wildlife than invasives? Insights from a community-level bird-exclusion experiment

Abstract

Abstract Biological invasions can threaten biodiversity by outcompeting native species and disrupting food webs. Invasive species are now a leading driver of biodiversity and imperiled species declines worldwide. In temperate forests of eastern North America, understory plant communities are frequently dominated by invasive woody shrubs and trees. For many species of insectivorous birds and mammals, these invasive plants may threaten populations by providing less and/or lower quality food. Conservation practitioners expend significant resources to remove invasive plants, but evidence that such practices improve food abundance or quality to wildlife is surprisingly limited. Using a bird exclusion experiment, we compared arthropod abundance, biomass, and quality (protein content), and bird foraging intensity among four invasive and six native woody plant species in a Connecticut, USA forest. Analysis revealed instances where native trees were actually poorer foraging resources for songbirds than certain species of invasive shrubs. Some invasive species, such as honeysuckle (Lonicera morrowii), supported higher arthropod biomass and protein content than the native plants. Conversely, Japanese barberry had fewer arthropods overall and arthropods of lower protein quality compared to native shrubs. Contrary to predictions from other food web experiments, bird predation effects were of similar magnitude on native and invasive plants, demonstrating that insectivorous songbirds foraged as intensively on the invasive plants as they did on the native plants. We recommend a more nuanced, regionally tailored and species-specific approach to invasive plant management that targets species that provide low-quality foraging opportunities relative to the quality of the local native plant community.