Photo: Jan Samanek, State Phytosanitary Administration, Bugwood.org
Even actions taken with the best of intentions can lead to unintended, unhappy consequences. The importation of plants now known to threaten native plant communities or damage agricultural lands offers many examples. Consider the buckthorns.
Common and glossy buckthorns are pleasant enough to look at. (The leaves on the first are toothed leaves, on the second toothless; both have short spurs on the branches which look like dull thorns; and their barks are nicely patchy-patterned.) They grow fast and just about anywhere, in sun or shade. And they produce enormous numbers of fruits each year.
Illustration by Anne Hunter
The (eventually) black fruits, which are just starting to ripen now, won't become palatable to birds until late autumn and early winter. (Immature fruits contain compounds which repel birds and which make humans gastrointestinally very uncomfortable). But late in the season other food sources will have been exhausted, and birds will need new sources of nutrition. Buckthorns have been advertised as "wildlife food" for decades.
So people planted buckthorns in North America, beginning at least as long ago as the late 1700s, because they were good-looking, they could tolerate difficult conditions, and, more recently, because they were good for birds and other animals. And what's happened? These species, native to Europe, Asia, North Africa and the middle East, have spread throughout most of North America east of the Mississippi. In some young forest and old field settings and in some disturbed wetlands the buckthorns have replaced native sapling and shrub communities and have shaded out wildflowers and native grasses and sedges. Landscapes of great variety and complexity and beauty have become impoverished stands of buckthorn.
Photo: Richard Webb, self-employed horticulturist, Bugwood.org
If you have buckthorns, the responsible thing to do is get rid of them. (They'll continue to be a source of seed for spread elsewhere otherwise.) Two methods seem to work well: girdling the stems of the shrub, and brushing the surface of a freshly cut stump with glyphosate (trademark Roundup™ or Rodeo™) herbicide.
To girdle the plant, deeply scrape away the bark from the entire circumference of all the stems, near their bases, to cut off transport of food and water throughout the plant. I've gone girdling in late autumn, after leaf fall but while the fruits are still present (they make identification easier). The cut stump method should be used for the next few weeks, while plants are still sending food reserves to their roots.