Non-native or alien invasive plant species are species introduced, either accidently or intentionally, into an area where they previously did not occur. A total of 222 non-native taxa occur in the preserve system. These non-native species are composed of 17 introduced, 33 adventive, and 173 naturalized. Thirty-six of these non-native species are considered by the Ohio Division of Natural Areas and Preserves (2000) as invasive and threaten natural areas. These non-native invasive species are a serious threat to the long-term viability of native plant communities. Euonymus fortunei, Ligustrum obtusifolium, and Polygonum cuspidatum currently are not invading natural areas from original introductions.
Lonicera maackii, a serious pest in the Cincinnati region, is found sporadically in the preserve system. At present, this species is not a serious problem but it is establishing in the preserve system. Phalaris arundinacea, a serious invasive species, was discovered at two locations along Ohio Brush Creek. This invasive species is locally a problem near the Swirl. Juncus inflexus was collected for only the second time in Ohio in a disturbed wet meadow (Cusick & Gardner 2002). This species is known from scattered locations in eastern United States and is not known to be a serious threat to natural plant communities.
One of the most troublesome species in the preserve system is Dioscorea batatas. This species is scattered throughout the preserve system and in some locations forms a extensive colonies similar to kudzu. Its prolific growth and fruit production make it a difficult species to eradicate. Ailanthus altissima is scattered in successional woods and has invaded barrens and promontories which were unexpected discoveries during this study. This colonial tree is increasing its frequency throughout the preserve system. Melilotus spp. are the most frequent invasives of barrens and promontories. Melilotus spp. will likely continue to increase in barrens, especially barrens near roads. Kudzu (Pueraria lobata) is not known to occur in the preserve system but occurs along Long Lick Road about 3.5 miles east of the preserve system.
Invasive species have a major effect on the flora altering habitat for rare plant and animal species. The preserve system has one of the largest collections of rare species in the state.