Southern Appalachian urban forest response to three invasive plant removal treatments

• Published in: Management of biological invasions 2016-11, Vol.7 (4), p.329-342
• Main Authors: Farmer, Sarah, Ward, Jennifer, Horton, Jonathan, Clarke, David
• Format: Article
• Language: English
• Subjects: Abundance; Celastrus orbiculatus; Community composition; Foliage; Hedera helix; Herbicides; Herbivores; Herbs; Indigenous species; Introduced species; Invasive plants; Land use; Light effects; Ligustrum sinense; Lonicera japonica; Native species; Plant communities; Population decline; Seedlings; Shrubs; Supplements; Toxicodendron radicans; Trees; Vines
• ISSN: 1989-8649; 1989-8649
• DOI: 10.3391/mbi.2016.7.4.03

Negative effects of non-native invasive plants have been well documented, but few studies have examined long-term impacts of non-native plant removal on both native and non-native plant community composition. This case study compared consequences of three non-native invasive removal methods (chemical, mechanical, and a combination of the two), applied to all exotic species, on native and non-native abundance, richness (total number of species), and community composition in two forested sites over six growing seasons. Important non-native vegetative components in pre-treatment and control plant communities included the vines English ivy (Hedera helix Linnaeus, 1753), Japanese honeysuckle (Lonicera japonica Thunberg, 1784), oriental bittersweet (Celastrus orbiculatus Thunberg, 1784), and clematis (Clematis terniflora De Candolle, 1817), and the shrub Chinese privet (Ligustrum sinense Lourero, 1790). In all removal treatments, non-native herbs, tree seedlings, and shrubs declined over six years, and native herbs’ and tree seedlings’ cover and richness increased. Time to implement treatments varied widely (844 person hours / ha for combination vs. 44 h / ha for chemical), but treatment effects only differed for native shrub density (highest in control treatment at one site), and native herb, shrub, and tree seedling richness (highest in mechanical and combination treatments at one site). Treatment did not affect cover or richness of non-native herb and tree seedlings, or shrub density and richness. Native species cover and richness increased as exotic species cover declined for all treatments in this study, suggesting that seed supplementation is not always necessary for community recovery. Spot-application of herbicides to foliage or girdled trees did not significantly hinder native plant community recovery, and no native species except poison ivy (Toxicodendron radicans (Linnaeus) Kuntze, 1891), which was intentionally removed, had its abundance or cover reduced by treatments. Even after treatment, clematis and Chinese privet remained important community components, demonstrating the difficulty in controlling these non-native species. Treatment effects were more pronounced at one site, perhaps due to imperfect selection of control plots, legacy land-use effects, or light limitation. This study supports the need for long-term treatment and measurement to accurately determine native plant community responses to non-native invasive removal.