Backyard Invasion

Tredyffrin homeowners are likely playing hosts to some unwanted visitors. Non-native invasive plants are spreading with abandon throughout Chester County, sprouting in backyards, parks, and preserved open space. To the casual observer, these plants may seem to be harmless weeds, or even desirable garden plants that have gotten a bit out of hand. In some cases, that may be true. The real threat lies in species that share a few common characteristics: aggressive growth habits, rapid reproduction, a lack of natural predators, and the ability to out-compete native plants for sunlight and nutrients.

In some cases, these invaders seem to be beneficial to wildlife by creating impenetrable thickets that provide food and shelter. White-tailed deer, in particular, find refuge in stands of multiflora rose and other invasive shrubs. But native songbirds, the insects on which they feed, and other plants and animals that used to be common in southeastern Pennsylvania are being displaced as invasive species spread at a pace far faster than the native species can adapt to them. The result is less wildlife diversity and impaired habitat for the species that have historically thrived in this region. Oftentimes, control of invasive plants becomes a costly and time-consuming problem for municipalities that fail to respond to the problem quickly enough.

The list of invasive plants found locally is quite lengthy. A few examples may suffice to highlight the scope of the problem for the average Tredyffrin resident:

	Garlic Mustard (Alliaria petiolata)- Quite common throughout Chester County, garlic mustard is usually seen as a 2-foot high stem with triangular, toothed leaves, and clusters of small white flowers. The leaves give off a garlic odor when crushed. They produce abundant seeds, and a small colony can quickly spread to dozens of square feet in a few years. Garlic mustard crowds out native wildflowers in woodlands, and provides no value to native wildlife. Garlic Mustard: Chris Evans, River to River CWMA, www.forestryimages.org
	Maiden Grass (Miscanthus sinensis)- Miscanthus has been widely planted as an ornamental grass, and only recently has been recognized as invasive as it has "volunteered" in meadows, power line rights-of-way, and along roadsides. There are many clumps of Miscanthus growing along Yellow Springs Rd. in the northwestern portion of the Township. While there are cultivars of Miscanthus that are sterile and thereby less of a nuisance, there are many other ornamental grasses that provide a similar effect in the landscape without the same invasive tendencies. Miscanthus: James H. Miller, USDA Forest Service, www.forestryimages.org
	Burning Bush (Euonymus alata)- Euonymus is another shrub that has been widely planted in the residential and commercial landscape in past years, to the point where it is considered so common as to fall out of favor with landscapers. In the meantime, local woodlands are seeing Euonymus cropping up along their borders with residential backyards, often in place of native shrubs that have been devoured by deer. In the shade of the forest, Euonymus spreads quickly but does not provide the bright red fall color that makes it so popular in the planned landscape. Euonymus: James H. Miller, USDA Forest Service, www.forestryimages.org
	Norway Maple (Acer platanoides)- Fast-growing and very tolerant of poor soil conditions, this European import out-competes native maples in the forest. Its dense shade discourages growth of any plants in the immediate vicinity, to the detriment of native wildflowers, even shade-tolerant ones. The Norway maple's resilience has made it a popular street tree in urban and suburban environments, and it continues to be sold for that use today. Norway Maple: Paul Wray, Iowa State University, www.forestryimages.org
	Vines- here are both native and non-native vines in almost any patch of woods you may see. Grapevine and oriental bittersweet can grow up into the tree canopy, where they rob the tree of access to sunlight, potentially weakening it. They also raise the tree's center of gravity, making it more susceptible to high winds. It is not uncommon to find large trees that have fallen after a heavy storm, still wrapped in extensive vines that generally survive the tree's toppling. And the subsequent patch of sunlight that now reached the forest floor where the tree once stood will often play host to a new crop of invasive plants, and not a new crop of small trees as you might expect. Vine: Forest & Kim Starr, United States Geological Survey, www.forestryimages.org
	Mile-a-minute Vine (Polygonum perfoliatum)- Less of a problem for the average homeowner, mile-a-minute is by far the most noxious of the invasive plants listed here. As its name suggests, it grows very rapidly and can quickly form dense canopies over shrubs, small trees, and any other vegetation in its path. It has thorns which discourage hand-pulling, and its Asian origin means there are no natural predators to slow its growth. If this weed gets a start unobserved in a corner of a large property, it can quickly spread to the point where professional assistance and chemical controls are required to rein it in. USDA APHIS PPQ Archives, USDA APHIS PPQ, www.forestryimages.org

So what can be done to manage the spread of invasive plants? First is to increase overall awareness of the problem. Learn to recognize the difference between native wildflowers, non-invasive weeds, and invasive species. Where feasible, remove undesirable plants from your own property. Hand pruning and pulling is preferable; use chemicals as a last resort, and follow directions for application precisely.

Prevent the introduction of invasive plants into your landscape by becoming familiar with the growth habits of the plants you buy. The vast majority of plants available at local nurseries have no invasive tendencies, even though they may not be native to this area. Be aware of the plants you add to your landscape. Where potentially invasive ornamental plants already exist in your yard, consider replacing them with non-invasive varieties. There are many native species that are the equivalent in growth habit as well as spring and fall color, and which may also attract birds and butterflies. Native plants are enjoying a resurgence in popularity, and are more available commercially than they were a decade ago. Locally, Jenkins Arboretum is an excellent example of the beauty and diversity that is possible with native plantings.

Members of Tredyffrin's Environment Advisory Council are leading the way by planning a fall planting of native plants in the Valley Hills neighborhood of Paoli. Why not join them?

RESOURCES: There are countless online resources available on this subject. Here are a few that provide further information on invasive plants and native alternatives, including photographs and drawings for easy identification:

• Pennsylvania Department of Conservation and Natural Resources
• Morris Arboretum, University of Pennsylvania
• National Park Service
• Penn State University
• Natural Lands Trust - Search on "invasive plants". A visit to their Crow's Nest Preserve in northern Chester County is a great opportunity for both education and recreation.
• Directory of native plant nurseries in Pennsylvania
• Bird Habitat Recognition Program - Audubon At Home

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