Assessing the effects of Amur honeysuckle control on native plant communities in southwest Ohio after eight years

Background/Question/Methods

Amur honeysuckle (Lonicera maackii), an important invasive shrub in the Ohio River Valley and other areas in eastern North America, has a phenology and a dense canopy that in forests excludes native herbs and interferes with woody plant growth and regeneration. While land managers can and do remove established honeysuckle stands from forest understories, recovery of native plant communities is poorly understood. I established 1000-m² modified Whittaker plots, a design that uses nested plots, in four stands with a gradient of honeysuckle infestation intensities in a county park in southwestern Ohio in 2005. Honeysuckle canopies were removed by herbicides in fall 2005. Species richness and cover were monitored in 2005, 2006, 2007, 2009, 2011, and 2013, across entire growing seasons.

Results/Conclusions

Species number at each site, originally 55-65, climbed to 80-90 at most sites four years after honeysuckle removal. Six years after, species number began to decline, but then climbed again after eight years, perhaps in response to tree canopy gaps from ash (Fraxinus) mortality caused by the emerald ash borer. Herbaceous cover, initially 10-50%, climbed to a maximum of 75-120% but had declined somewhat from the peak levels by 2013. Rarefaction curves and Shannon indices indicate that species became more evenly distributed at all sites. Cover of the invasive herb garlic mustard (Alliaria petiolata) initially increased but then declined at all sites over the study period; however, total invasive species richness increased over the study period. While honeysuckle canopy removal appears to promote the recovery of native plant communities, ash mortality may alter this until tree canopy gaps are filled. Amur honeysuckle has regenerated at all sites, but this may be impacted negatively in the future by honeysuckle leaf blight, which was widespread over the region in 2012 and 2013 and appears to have caused some seedling and sapling mortality.