FRANGULA ALNUS INVASION, TREATMENTS, AND COMMUNITY RESPONSE

Author

• Christopher A. Hohnholt, Michigan Technological UniversityFollow

Date of Award

2026

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Forest Science (PhD)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Christopher R. Webster

Committee Member 1

Tara L. Bal

Committee Member 2

Michael A. Jenkins

Committee Member 3

Mari W. Buche

Abstract

Frangula alnus (glossy buckthorn) is an invasive shrub that exploits former agricultural lands left to revert to forests. This research investigated an invasion and three treatments (physical removal, chemical treatment with glyphosate, and chemical treatment with triclopyr) for F. alnus on a 6-hectare site in Houghton County, Michigan. The site included a remnant northern hardwood woodlot, a Pinus sylvestris (Scotch pine) plantation, and an abandoned field colonized by Fraxinus americana (white ash).

To investigate the invasion dynamic, we examined the height structure and minimum age of the invasion spatially, as well as factors such as overstory and understory composition, light availability, soil characteristics, and proximity to edges. We observed the greatest densities of glossy buckthorn on plots associated with past agricultural use and abandonment. In our research site, these were the plantation and the abandoned field.

We then evaluated the effects of different treatments on both F. alnus and associated plant communities by removing shrubs with hand tools or applying herbicide treatments of glyphosate or triclopyr. Surveys of F. alnus abundance and ground-layer vegetation were conducted prior to treatment and for two years post-treatment across the land uses. Plant community responses were quantified using species richness, evenness, Shannon diversity, and floristic quality index. Nonmetric multidimensional scaling ordination and multi-response permutation procedure revealed distinct ground-layer plant communities among land-use classes. Physical removal and triclopyr provided the most effective F. alnus control; however, physical removal was associated with an initial increase in ruderal species, while triclopyr caused temporary declines in plant community diversity and quality indices. These results indicate the management outcomes depend on prior land use and plant community composition, and that selecting control methods requires consideration of both F. alnus suppression and broader ecological effects.

We then evaluated the cost-effectiveness of the treatments. Using plot-level costs, reductions in plant height and aerial cover, and the number of plants removed per dollar spent, we quantified treatment efficiency. We found that although mechanical treatments costs’ were higher and far more variable, there were no statistical differences among the efficiency calculations. Our approach highlighted differences in outcomes 1 and 2 years post-treatment, providing managers with actionable insights to select economically efficient strategies for controlling glossy buckthorn in forested landscapes. Managers might find that the details of the invasion—including plant heights, density, and age—provide context necessary for considering treatments.

Recommended Citation

Hohnholt, Christopher A., "FRANGULA ALNUS INVASION, TREATMENTS, AND COMMUNITY RESPONSE", Campus Access Dissertation, Michigan Technological University, 2026.

https://digitalcommons.mtu.edu/etdr/2180