Invasive populations of Japanese barberry (Berberis thunbergii DC.) are currently found in 30 states across the United States (Anonymous, 2007). Barberry plants are established from seed, which is primarily dispersed by birds and small rodents (Decker et al., 1991; Silander and Klepeis, 1999). Feral seedlings may form impenetrable thickets that displace native flora (Clark et al., 1998) and alter soil chemistry, microbial communities, and earthworm populations (Ehrenfeld et al., 2001).
Since its introduction to U.S. cultivation in the late 1800s, Japanese barberry has become one of the most popular horticultural plants as a result of its hardiness, ease of culture, resistance to deer browsing, and general attractiveness (Steffey, 1985). This plant holds substantial market share in the U.S. commercial horticulture industry, and in Connecticut alone, the barberry crop is worth $5 million in retail sales (Heffernan, 2005). Current cultivated forms of Japanese barberry (B. thunbergii var. atropurpurea) have purple foliage, whereas feral barberry have green leaves and plants resemble the species, B. thunbergii, which is rarely found in cultivation today.
Japanese barberry bans in Massachusetts (Anonymous, 2005) and New Hampshire (Anonymous, 2004) and those being considered by other states across the United States do not differentiate between the species and its purple-leaved forms (Harrington et al., 2003). Because it is uncertain whether the offspring from cultivated purple-leaved genotypes establish in natural habitats, legislation banning all Japanese barberry is controversial.
The objective of this study was to determine the degree to which a purple-leaved barberry in a residential landscape can contribute offspring to a surrounding invasive population or initiate a new invasion in adjacent unmanaged areas. For this work, we identified a location where a purple-leaved barberry used as a landscape plant was surrounded by feral barberries of various ages and sizes invading unmanaged land. Amplified fragment length polymorphism (AFLP) parentage analysis, in combination with morphological and spatial information, was used to determine the extent to which the cultivated landscape plant had contributed to the surrounding feral barberry population.
Anonymous 2004 Adopted rule. Chapter Agr 3800 Invasive species State of New Hampshire Nov. 2007 <http://www.nh.gov/agric/divisions/plant_industry/documents/Rules_8.pdf>.
Anonymous 2005 Massachusetts prohibited plant list State of Massachusetts Nov. 2006 <http://mass.gov/agr/farmproducts/Prohibited_Plant_Index2.htm>.
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