Invasion of deciduous forest preserves in the New York metropolitan region by Japanese barberry (Berberis thunbergii DC)

Japanese barberry has become a common component of understory vegetation in deciduous forests throughout central and northern New Jersey and adjacent areas of Pennsylvania and New York. A survey was carried out by soliciting data from the public concerning the occurrence of the plant in forest preserves in the New York metropolitan region. The resulting information showed that this exotic species is present within the forest interior in at least 43 protected forest areas. In the majority of these areas, the species occurs in extensive patches of moderate to very high density. Although known to some resource managers, the spread of this exotic species into intact forest has not previously been reported. The widespread growth of B. thunbergii may threaten the ability of small to moderate-sized forest reserves to serve as a refuge for native plant species.