There's an invasion in progress and very likely, your back yard is harboring some of the "alien" life forms stirring new opposition from those who wish to preserve native flora and fauna. These invaders are usually attractive, often invited, and may already be part of your landscape.
I'm talking about introduced plants that are not native to the area in which you live. They may be familiar -- Norway maple, English ivy and multiflora roses are examples -- but they are not the plants with which nature originally sowed the land. Some avid gardeners don't want them growing here.
In a Web posting on recognizing and controlling non-native plants, the Maryland Native Plant Society is unequivocal: "Many of the plants in this guide are popular, even beloved, landscape plants, but it is now clear that they pose a threat to our environment. If you cannot effectively contain these plants within your property, by clipping seeds, fruits, or runners, please consider removing them."
The site lists native and non-native plants considered to be invasive and includes specific methods, including mowing, burning and herbicides, to rid your property of these invaders, noting, "It is a difficult decision, but each of us has a responsibility not to damage the local ecosystem that cleans our air and water, stabilizes the soil, buffers floods, and provides food and shelter for innumerable species besides our own. Each of the non-native plants in this guide significantly reduces the number of plant and animal species on any site it invades."
How big a threat are these plants? Not all of them arrived unbidden and unwelcome. Some were brought from other parts of the country, or other parts of the world, precisely because they were ornamental, hardy and prolific.
For instance, Bradford pear trees, with their white flowers, have been widely used as street trees. Crown vetch, a dense thatch of pink-purple clover-like flowers, was extensively planted as a groundcover along highways. Purple loosestrife, with its tall spikes of long-lasting pink or purple flowers on leafy spike-like racemes, makes a great garden plant.
Not all troublesome plants are imported. Common reed (Phragmites australis), with its lovely, tall plumes, forms dense monocultures, especially in wetlands and in roadside ditches. Even though it's a native, it is considered a pest.
The problem with these and other invasives is that they don't stay along sidewalks, or by the interstates, or in the garden. They have an amazing variety of ways to reproduce, including wind- and animal-borne seeds, wind- and insect-borne pollen, nuts and berries that fall off and take root, or underground (and even under pavement) runners. They can easily end up in areas where they quickly dominate native plants.
It's the domination that is a problem, as these plants crowd out local species on which resident birds, insects and animals depend. Habitat reduction is a big step on the road to extinction.
So yes, they can be a problem. Yet some invasive, introduced plants are common ornamentals that have been used for years and are well entrenched.
