Audubon Center for Native Plants
Invasive Plants Information
What are invasive plants?
Invasive plants are species that are both non-native to our area, and present a threat to native species by crowding them out or inhibiting their growth. The non-native invasives do not provide the same value to the wildlife and other plants in the ecosystem as the natives did. This leads to an overall loss of diversity as the negative effects ripple throughout the ecosystem. In our gardens, we see this on a smaller scale when our favorite vegetable patch is overrun by a pesky weed. The same thing can happen to an entire forest, for example, if an invasive tree species is not removed. In Pennsylvania, the invasive problem is compounded by our large deer population. The deer avoid invasives, eat natives, thereby removing the invasives' competition in a downward spiral.
Are all non-native plants bad?
No, some non-native plants do not present a significant risk. Many ornamental species used in flower gardens, for example, do survive Pennsylvania winters. Other imported species such as Queen Anne's Lace have naturalized, but generally do not cause significant problems. Even so, non-invasive yet non-native species do not provide the same value to the local environment as the native plants. This is why we encourage using native plants wherever a suitable option exists. See our Audubon Center for Native Plants for more information on selecting native plants.
What can I do about invasive plants?
Whether it be it your own yard, an empty lot or a natural area you visit, take these steps if you have permission or assist the landowner:
Learn which invasive species are in your area. There are quite a number on the state list of invasive species--but only a handful may be threatening a given property at present. Start with the obvious ones.
Avoid spreading them. Some of these species are still available at garden centers--don't buy them! Don't unwittingly encourage ones you already have to spread.
Remove them wherever you can--but in the best way for the species. Sometimes simply pulling them is sufficient, or a change in mowing schedule, but for some the best solution may be an eco-friendly herbicide.
Improve the habitat that remains. The invasives will quickly return unless there's something there to stop them. Replaced what was removed with appropriate native plants. Remain vigilant for returning invasives.
What are some invasive plants I should be watching for?
There are quite a number of invasive plants threatening Pennsylvania, but here are a sample some that are of greatest concern in southwestern PA. This is a only partial list--see the links below for more information and removal tips.
Garlic Mustard -- a woodland wildflower that crowds out spring ephemerals. Flyer (PDF)
Japanese Knotweed -- a large shrub that grows so dense nothing else will survive. Frequently found along river banks, but will grow nearly everywhere there is sun.
Tree of Heaven -- a fast-growing tree that chemically inhibits other trees from germinating near it.
Asiatic Bittersweet -- a vine that overwhelms trees and displaces out native and better-behaved American Bittersweet.
Japanese Honeysuckle -- a shrub that grows in the forest understory
Japanese Barberry -- commonly planted for hedges, this thorny invasive crowds the forest understory
Burning Bush (Euonymous) -- a popular yard shrub that escapes into the woods to crowd the understory
Autumn Olive -- another shurb invading forests and old fields
Purple Loostrife -- a wetland invasive threatening delicate wetland ecosystems statewide
Phragmites -- a wetland plant that displaces native cattails, but has little wildlife value compared to cattails.
Where can I get more information?
Pennsylvania DCNR, Penn State University, the US Department of Agriculture and similar agencies across the nation have developed resources for identifying and removing invasive plants. Here a few excellent resources specific to Pennsylvania to get you started.
- DCNR Invasive Plants brochure (PDF) -- A color brochure providing more information on invasives across the state and a list of plants organized by region.
- Invasive Exotic Plants In Pennsylvania List -- PA DCNR Fact sheet and management strategies for many of most important invasives. From the tutorial linked below.
- DCNR Invasive Exotic Plant Management Tutorial for Natural Lands Managers -- A very thorough treatment of the issue written for land managers, but of interest to any land owner.