Effect of Manual Ivy Removal on Seedling Recruitment in Forest Park, Portland, OR

Abstract

English and Irish ivy (Hedera helix and H. hibernica) are invasive lianas which have become especially intrusive in the Pacific Northwest, as evidenced by their invasion of many areas in Forest Park, Portland, OR. The most common strategy for ivy control is currently manual removal, though the potential consequences of this method have not been well studied. The purpose of this study was to evaluate the effectiveness of manual ivy removal with respect to its influence on native plant diversity, abundance, species richness, and evenness by comparing these parameters in 1-m2 plots manually cleared of ivy to paired control plots. Prior to plot establishment, evidence of deer herbivory of ivy was observed at this site. Four weeks after manual removal, treated plots were less diverse and hosted a lower abundance of native plants than control plots. Ten weeks after ivy removal, treated and control plots were equally diverse, and treated plots showed greater abundance of plant cover than controls. This trend persisted at twenty-six weeks after treatment. Treated and control plots were not significantly different in species richness or evenness at any time. These results suggest that manual ivy removal temporarily disturbs native plant life, but the negative effects are overcome as quickly as ten weeks after treatment, at which time native plants are more successful. Manual removal as a method to control ivy in this region appears effective within one growing season. KEYWORDS: English Ivy, Irish Ivy, Invasive Species, Pacific Northwest, Forest Park, Hedera helix, Hedera hibernica