MARCH 2012

The Invasion of Phellodendron amurense into the Urban and Suburban Woodlands of the New York City Region

by Eric C. Morgan and Jon A. Borysiewicz

Bartlett Arboretum, 151 Brookdale Rd., Stamford, CT 06903


Phellodendron amurense Rupr. is an introduced, exotic tree species from eastern Asia which has been used in ornamental horticulture in urban and suburban areas throughout the Northeast. In recent years, even as more focus has been placed upon the impact of invasive species, Phellodendron amurense and other non-native species have continued to be planted, and little or no examination of their potential impact and spread has been undertaken. In 2008 and 2009, surveys were performed at sites where Phellodendron amurense was reported to have been found growing adventively. From these sites, five invasions of reproducing populations were identified and investigated further. These five sites, located in Bronx County, New York; Fairfield County, Connecticut; Philadelphia County, Pennsylvania; Queens County, New York; and Tolland County, Connecticut, were then investigated for similarities in their forest composition that may help to explain forest susceptibility to invasion by P. amurense. This work reports that P. amurense is a much more widespread invader than previous literature suggests, and that the invasion is not limited to any particular forest type. The five main invasion sites examined here do not share the same top species in importance value calculations, and correspondence analysis shows little similarity between four of the five sites. Tree density, which ranges from 55 to 643 trees per hectare, is also shown not to affect P. amurense's ability to invade a particular site. These data provide strong evidence of the need for close monitoring and potential removal of P. amurense before populations in the region reach a point at which removal will no longer be an option.

Keywords: Invasive species, New York, Philadelphia, Connecticut, New Jersey, importance values, Phellodendron amurense, Rutaceae