GWERD Research on Impacts of Invasive Plant Species on Human and Ecological Health

Invasive and exotic (non-indigenous) plant and animal species are biological pollutants that threaten ecosystem and human health, causing estimated billions of dollars in economic costs. For example, eastern redcedar, a focus of our studies, is an invasive evergreen tree that displaces native plants, reduces habitat quality, alters groundwater hydrology, and creates dense pollen plumes that exacerbate allergies and asthma. Identifying the effects of invasive species on ecosystems and understanding the mechanisms of invasion will be critical to developing risk management strategies for limiting the economic and environmental damage caused by invaders.

Publication: Invasive grass alters litter decomposition by influencing macro-dectritivores. Mayer, P., S.J. Tunnell, D.M. Engle, E.E. Jorgensen, and P. Nunn. This research demonstrated the complexities behind the effects of invasive species on ecosystem processes. Our research showed that 1) excess nitrogen accumulates in terrestrial ecosystems in a way that can harm ecological health, 2) an invasive, exotic grass (Festuca arundinacea) can alter the way in which that nitrogen accumulates in the environment, and 3) insects and other litter decomposers are important to the nitrogen cycling function of ecosystems.

Field Project: Quantifying and modeling the risk of disturbance to ecosystems caused by Eastern Redcedar (Juniperus virginiana). (Contact: mayer.paul@epa.gov) Eastern redcedar (Juniperus virginiana) and its associated vertebrate seed dispersers were studied in the field and in a greenhouse to identify fundamental mechanisms of plant invasion. We are investigating whether or not invasion of eastern redcedar might be exacerbated by excess nitrogen in the environment and if certain ecosystems are more susceptible to invasion either due to seed dispersal or because eastern redcedars grow faster in some ecosystems.

Publication: Differential frugivory of eastern redcedar (Juniperus virginiana) by avian and mammalian guilds. Horncastle, V. J., E. C. Hellgren, P. M. Mayer, D. M. Engle, and D. M. Leslie, Jr. Our research showed that oak-hickory forests (cross timbers) may be far more susceptible to invasion than other ecosystems because mammals preferentially consume and then deposit the seeds of eastern redcedar growing within cross timbers sites. Efforts to selectively remove eastern redcedar from cross timbers habitats may reduce the rate of eastern redcedar invasion.

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