New ecological interaction: Herbivory of Japanese knotweed by White-tailed Deer

Japanese knotweed (Reynoutria japonica Houtt) is a successful invasive species for a multitude of reasons that include: anthropogenic cultivation, vegetative reproduction, allelopathy, and competitive exclusion, as well as enemy release from native herbivores. An adequate biological control agent has been sought to help control its dominance and spread, though the most recent control agents have failed to establish and control the plant in field studies. This paper represents hope that R. japonica can be controlled or have its dominance reduced on the landscape by a dominant North American herbivore, the white-tailed deer. Our study confirmed that a population of white-tailed deer in Central New Jersey are intentionally and significantly consuming R. japonica to a level that alters the growth of the plant. Our results support the findings of other studies in that R. japonica reduces species richness within the plant community and reduces the area covered by other plants. We did not find a relationship between the amount of plant damage (leaves lost) to canopy coverage of R. japonica, likely because the plants growth form still produces shade by becoming stout with more branching rather than tall and overhanging. The herbivory of R. japonica by this population of white-tailed deer likely stems from an unusually high population density of deer in this suburban area that drove them to seek alternative food resources. This study is another example of the ability of native herbivores to eventually form new relationships with invasive plants, and it provides hope for the biological control of R. japonica by native species in the future.