Helping invaders migrate

Monday April 30, 2012

Until we know the value of our native plants, how can we to be expected to care much about the damage caused by invasive nonnative species? Until we actually see a stately 50year-old tree strangled by Oriental bittersweet will we ever understand that we can't blame its march across the country entirely on birds?

Especially if we gathered it in the autumn to bring home for fall or winter decorations, only to toss it outside when no longer wanted.

Food for the birds and animals we say. Exactly. We may have transported it 40 miles to "ground zero' and from there birds and small rodents spread it all about.

Farfetched? I recall some years ago, before it became widespread, Oriental bittersweet grew along the east side of Route 7 in Great Barrington near Monument Mountain. North County folks would gather it to take to Lenox, Pittsfield and points north, east and west. A simplification, but it is an example of how an invasive gets our help.

Similarly, the pioneers brought "flannel wort" with them from their New England and Virginia gardens as they pushed westward across the Alleghenies to Ohio and eventually all the way to the Great Plains and beyond. Today we call the plant mullen, and it has continued its march.

Another plant that has received our help in more recent years is autumn olive, a shrub touted for wildlife planting as well as screening. Unfortunately after government agencies and university extension services proclaimed its virtues and municipalities planted it, homeowners planted it, and conservation clubs and societies planted it, we discovered it rapidly spread on its own, to nearby fields and hillsides crowding out diverse natives.

Birds eagerly eat its fruits, thus spreading seeds even further afield. I know of two local conservationminded organizations that sold autumn olive seedlings in the 1980s.

I was involved with one. Today, established stands require a combination of pulling, cutting, and herbicides.

Promoted as a "living fence," multiflora rose now creates impenetrable thorny undergrowth that requires mechanical pulling and herbicides to stop its progression. ( I shudder every time I type the word herbicide, incidentally.) I now know the "wild bamboo" of my youth as Japanese knotweed, and wherever it grows, it harms the habitat, especially along waterways, but also in vacant lots, yards and anywhere else it gets a footing. It easily spreads by underground rhizomes as well as pieces of broken-off stem.

A minimum of four cuttings during the growing season will often eliminate the underground energy reserves of a stand. Digging is also an effective means of elimination an newer invasions.

The lovely purple loosestrife, once a favorite among city street vendors, has escaped to destroy the value of many a wetland, eliminating native species so necessary to a thriving semi-aquatic community.

It is almost impossible to eliminate by digging and pulling, but this does limit its seed production. At present, biological control (also alien), appears to be out best bet in the fight against this invader.

Questions and comments for Thom Smith: Email


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