Common buckthorn (Rhamnus cathartica) invasion exacerbates white-tailed deer (Odocoileus virginianus) browsing on native woody plants

Selective feeding by overabundant herbivores can considerably alter plant
community composition and structure, often benefiting non-native species.
White-tailed deer (Odocoileus virginianus) are a dominant herbivore in
North America, known for their preference for native plants over
unpalatable invasive species. Common buckthorn (Rhamnus cathartica), a
widely invasive shrub, is largely avoided by deer, potentially
facilitating its competitive advantage against native plants. This study
investigates the interactive effects of buckthorn invasion and deer
browsing on native woody plants within a post-industrial urban forest
undergoing restoration. Specifically, we employed both a long-term
observational tree survey and an experimental shrub study to assess
buckthorn impacts on native trees and shrubs, and to investigate whether
buckthorn presence intensifies deer browsing. For the tree study, we
surveyed ten native tree species planted in areas with varying levels of
buckthorn invasion to assess tree health as a function of buckthorn and
canopy tree cover. For the shrub study, we examined deer and insect
herbivory on five deer-resistant native shrubs with and without deer
exclusion and buckthorn removal. We found that increased buckthorn cover
correlated with reduced health in native tree species, a relationship not
found between the trees and native canopy tree cover. We also found that
all five planted native shrub species experienced considerable browsing,
with deer and insect damage intensifying in the presence of buckthorn.
This study highlights the complex interplay between non-native plant
invasions and native herbivore activity, demonstrating that buckthorn
indirectly facilitates increased deer herbivory on native species. These
findings emphasize the need for integrated forest restoration strategies
that address both invasive plant removal and herbivore management to
support native species recovery.