Japanese barberry which is the one commonly sold is an invasive exotic species.
It is currently found to be invasively present in 43 protected forest sites in New York State. Connecticut has declared Berberis thunbergii to be "probably one of the most destructive invasive plants in CT."
ECOLOGICAL THREAT: Japanese barberry forms dense stands in natural habitats including canopy forests, open woodlands, wetlands, pastures, and meadows and alters soil pH, nitrogen levels, and biological activity in the soil. Once established, barberry displaces native plants and reduces wildlife habitat and forage. White-tailed deer apparently avoid browsing barberry, preferring to feed on native plants, giving barberry a competitive advantage. In New Jersey, Japanese barberry has been found to raise soil pH (i.e., make it more basic) and reduce the depth of the litter layer in forests.
DISTRIBUTION IN THE UNITED STATES: Japanese barberry has been reported to be invasive in twenty states (CT, DE, IN, KY, MA, MD, ME, MO, NC, NH, NJ, NY, OH, PA, RI, TN, VA, VT, WI, WV) and the District of Columbia.