“Invasive species have the potential to completely alter habitats, disrupt natural cycles of disturbance and succession, and most importantly, greatly decrease overall biodiversity, pushing rare species to the brink of extinction. Many ecologists now feel that invasive species represent the greatest current and future threat to native plant and animal species worldwide, greater even than human population growth, land development and pollution.” William Cullina of the New England Wildflower Society
We do not have to travel far to see the power of invasive plants. Look at local wetlands filled with the plumy spikes of purple loosetrife. Drive along I-91 coming into Greenfield from the south in the fall and see all the Oriental bittersweet climbing trees along the highway. See the acres of Japanese knotweed blooming in the fall along the roadsides.
Where and how did these exotic invasives get their start? This simple question has a multifaceted answer.
Over the past 300 years non-native plants have found their way to North America in a variety of ways. Some have come accidentally. Agricultural weeds have come in grain shipments, or in the ballast of early ships. Others have been introduced by horticulturists, and even the government.
As recently as 25 years ago I ordered several Autumn Olive (Eleagnus umbellaata) shrubs from the Conservation district. They grew well for several years, but eventually died, probably because of the competition by the wild grape vines I am always fighting. They died, but it took me a while to notice that they had seeded all over the sloping field to the east of the planting. I assume this is one of those un-intended consequences that befall all of us from time to time – but it is making a lot of work for us now.
Burning bush (Euonymus alatus) is a shrub that can still be found at nurseries even though it is on the invasive list of plants in Massachusetts. The brilliant red fall foliage and its dependability are the reasons for its popularity.
So what can gardeners do? We choose plants like burning bush and purple loosetrife because of their beauty and because they suit our site.
First, gardeners have to educate themselves about which plants must be avoided. They can check the list on the New England Wildflower Society website, www.newfs.org. This site will not only list invasive plants, it will suggest native plants that provide many of the same attributes. For myself, I have never really liked burning bush, and my highbush blueberries give the same red fall foliage – and blueberries.
Other alternatives to burning bush include Cotinus obovatus, the American smoketree. Many people plant this large shrub because they like the plumey ‘smokes’ in the fall. The deep red color is there all season long. Sweetspire, Itea virginica, is a smaller shrub if you have less space, and Clethra alnifolia, summersweet, gives you wonderfully fragrant flowers in summer as well as autumnal color.
This summer I was in Buffalo to get a preview of the fantastic Buffalo Garden Walk tour. One of the ‘hell-strips’ that my colleagues exclaimed over included purple loosestrife, half of us not recognizing it among the mixed planting of phlox, echinaceas and other perennials. It is a beautiful plant but so dangerous. Alternatives of Lythrum salicaria and L. virgatum, include Gayfeather, Liatris pynostachya and Filipendula rubra otherwise known as Queen of the Prairie which is a good strong grower, but not invasive. If you have a wet site swamp milkweed, Asclepias incarnata with its clusters of pale to deep rose on tall stems might be an answer.
The climbing tree in front of the Buckland Library is a Norway maple. This has been identified as such an invasive species that many public gardens and parks like Central Park in New York City have cut down all their Norway maples. It was planted to give children a good climbing tree. With the new library addition and new landscape that tree will need to be removed, but I suspect it will be replaced – and this time with a non-invasive climbing tree. I have been told that mulberry trees (and there are fruitless varieties) are good for climbing, as are apple trees. There are a lot of apple trees in Buckland orchards, so this might be an appropriate tree – especially if someone volunteers to prune it during its youth to accommodate young climbers.
Other good native trees for the domestic landscape include Yellowwood (Cladastrus kentukea) which has flowers in spring and golden fall color, several birches, river birch as well as paper and sweet birch. Crabapples and mountain ash feed the birds.
In his excellent book, Bringing Nature Home: How Native Plants Sustain Wildlife in our Gardens, which I cannot recommend too highly, Douglas W. Tallamy makes the point that even suburban gardeners play an important part in providing food and shelter for the wildlife that we welcome into our gardens, and maintaining a healthy balanced ecosystem.
That sounds reasonable – and easy, but we have to provide food that native wildlife find edible. We also need to pay attention to feeding all stages of these creatures’ lives. Butterfly larvae need to eat too.
Using native plants does not limit us to a few uninteresting varieties, but we will need to be aware of their importance, and then educate ourselves. There are many resources on the Internet and at your library and bookstore. In addition to Tallamy’s book the Brooklyn Botanical Garden has an excellent small book Native Alternatiaves for Invasive Plants. Happy reading.
Between the Rows August 28, 2010