The Invasion Ecology of Japanese Barberry (Berberis thunbergii) in the New England Landscape

Japanese barberry (Berberis thunbergii) has been characterized as one of the most widely known and planted exotic shrubs in the United States. It was first introduced to the US in the late 1800s. By 1920 the planting of Japanese barberry was encouraged as an ornamental shrub replacing the common barberry (Berberis vulgaris). Japanese barberry began spreading from cultivation in suburban and selected rural retreats by the 1920s, and had dispersed rapidly throughout the northeast by the 1960s. By the 1970s it was recognized as a problematic invasive in the northeast. It is readily dispersed primarily by birds. Fruit production varies with light level, but even under very low light levels (4% full sun) some seeds are produced. Fruits are dispersed in late fall through late winter. Seed dispersal curves are highly leptokurtic; most seedling are found under or adjacent to adults, but a small number may be found tens of meters from the nearest adult. Japanese barberry thrives under a broad range of light and soil moisture conditions. Significant variation in stem growth can be explained as a function of light level. Even at less than 1% full sun, some positive stem growth can occur. Survival is quite high at intermediate to high light levels, and only under the lowest light levels (<1% full sun) does survival drop significantly. Biomass of Japanese barberry in field plots can be largely explained as a function of light availability and soil moisture. The biomass of co-occurring species is suppressed by Japanese barberry, and recovery is slow in the first year following Japanese barberry removal except under high light levels. Glyphosate (Roundup) applied in early spring at first leaf out, when little else is in leaf, provides an effective means of eradicating Japanese barberry populations.