The Establishment, Control, and Post-Control Response of Amur Honeysuckle (Lonicera maackii)

Amur honeysuckle (Lonicera maackii) is a shrub endemic to East Asia which has become invasive and nearly ubiquitous to the forest ecosystems of eastern North America. Through its extended growing season, competitive ability, and potential allelopathy, Amur honeysuckle alters native herbaceous-layer plant communities and inhibits the regeneration of native tree species. As such, it is representative of a range of invasive shrub species imported from East Asia. My thesis contributes to questions fundamental to the understanding this and other invasive shrubs: 1) How do species become invasive? 2) How can the invasions of the species be effectively controlled? 3) How does the ecosystem respond to treatment of the invasive species?

First, I examined the role of self-compatibility within Amur honeysuckle. I compared the berry production, seed production, and germination rates between closed-pollinated and open-pollinated flowering branches of Amur honeysuckle individuals across multiple types of invasions (heavy, light, and sprouting). I found that Amur honeysuckle not only possesses the ability to self-pollinate, but that it can produce viable self-pollinated seed sets. This ability may help explain how Amur honeysuckle able to invade isolated forest patches far removed from the main invasion.

Second, I evaluated the effectiveness of a novel herbicide adjuvant in reducing the amount of herbicide needed in the ‘cut-stump’ method of controlling Amur honeysuckle. Combining various concentrations of the most common herbicide in the world, glyphosate, with concentrations of cellulases derived from fungi, 2XL, I examined whether the cellulases improved the effectiveness of glyphosate, potentially by increasing glyphosate movement into the vascular tissue of Amur honeysuckle through the degradation of cell walls. While 2XL was not an effective adjuvant, glyphosate concentrations of less than half the recommended dosages were equally effective as higher concentrations in preventing sprouting of treated stumps. The ineffectiveness of 2XL may imply a need for protein-mitigated diffusion of glyphosate across cell walls and into the vascular tissue of the plant, which would be inhibited by the breakdown of cell walls.

Finally, I tested how deeper intensities of mulching-head treatments affected the sprouting response of Amur honeysuckle and the response of the herbaceous-layer plant community after treatment. I found a negative relationship between the volume of sprouting Amur honeysuckle and increasing depth of mulching-head treatment. Additionally, increasing mulching-head intensities were correlated with increased herbaceous layer diversity and conservation value as represented by Floristic Quality Index. Mulching-head treatments are a promising tool in controlling heavy invasions of non-native shrubs.