Non-Native Invasive Species

Japanese barberry

Berberis thunbergii

Japanese barberry was introduced to North America in 1875 (it is in fact from Japan), when seeds were planted at the Arnold Arboretum in Boston. The species adjusted very successfully to its new surroundings, so much so that it now grows in abandoned fields, pastures, wetlands, woodlots, and forests from Boston to Missouri, to Maine, and to North Carolina. Many woods in southern Vermont and nearby Berkshire County, Mass. are so thoroughly colonized by the prickly plant as to be impenetrable. (In fact, The Nature Conservancy in Berkshire County has sponsored a barberry eradication research program for at least two years.)

Japanese barberry

Japanese barberry
Photo: Richard Old, XID Services, Bugwood.org

Some people blame the bunnies - and turkeys, and other small mammals and birds - which disperse the seeds. (It is interesting to think that the spread of barberry and rebounding populations of turkeys might be related.) But it started with gardeners.

And why not? The shrub grows in sun or shade and in wet or dry soils. It has few serious pests. Its thorns make it useful for barrier and privacy plantings. Its brilliantly scarlet ripe berries are hugely ornamental. And its fall foliage is red and yellow and orange. A row of Japanese barberries along the driveway or property line, a cluster of barberries in the shrub border, or a single shrub at the corner of the house all were and still are popular landscaping choices.

Japanese barberry

Japanese barberry
Photo: Leslie J. Merhoff, University of Connecticut, Bugwood.org

Such plantings are no threat to the cultivated landscape around one's home, and they are probably an insignificant threat to wild lands - at least compared to all the barberry plants growing in the wild and the seed they produce. Still, we should stop planting the species. (Its sale is illegal in Canada.) And where we find it in the wild, we should remove it.

Small seedlings can be pulled by hand. Larger shrubs will require the use of a spade or a weed wrench (and protective clothing). Large infestations are best controlled by burning (in open areas) or by the use of herbicides such as glyphosate (Round-up™ is a tradename) in wooded areas.

Japanese barberry

Japanese barberry
Photo: Richard Old, XID Services, Bugwood.org

Our region also hosts another thorny alien. Despite its name, common barberry (Berberis vulgaris) is not as common as Japanese barberry (B. thunbergii), though it is common enough to be a problem, especially in sunny sites. Common barberry carries dangling, inches-long clusters of several berries, and has toothed leaves. Japanese barberry leaves are smooth-edged. Its umbrella-shaped berry clusters usually contain few fruits.