Invasive Plants

Did you know that out of the 50,000 introduced plants in the United States nearly 5,000 are wreaking havoc on our environment? Invasive species are second only to habitat destruction, such as by fire or land clearing, for displacing native plant and animal communities and altering entire ecosystems. They out-compete native species for food or other resources: e.g. the Japanese Barberry alters microbial activity in soils, increases soil pH, and reduces forest leaf litter. Some cause or carry disease that affects the health of native species: e.g. Hemlock Woolly Adelgid, an insect pest from Asia, kills eastern hemlock trees.

Some invasive plants have been introduced accidentally, one example is Mile-a-minute. Some species were introduced for wildlife benefits such as Multiflora Rose and Japanese Honeysuckle; or for erosion control like Japanese Knotweed; or for medicinal and/or food use such as Garlic Mustard. Others have escaped from our gardens like Purple Loosestrife, a Pennsylvania noxious invasive plant that devastates waterways.

Once they establish in natural areas their ability to propagate in several ways and to thrive in many conditions allows them to spread rapidly. Because they have few or no natural enemies in their new home they can usually out-compete native plants. This upsets the delicate balance of local ecosystems and affects the insects and pollinators dependent on the natural habitat.

Plants that are classed as a “Severe Threat” in Pennsylvania:
Tree-of-Heaven, Garlic Mustard, Porcelain Berry, Japanese Angelica, Japanese & European Barberry, Oriental Bittersweet, Poison Hemlock, Giant & Hybrid Knotweeds, Lesser Celandine, Glossy Buckthorn, Goatsrue, Giant Hogweed, Japanese Hops, Japanese Honeysuckle, Purple Loosestrife, Japanese Stiltgrass, Wavyleaf Basketgrass, Mile-a-Minute, Common Reed, Kudzu, Common Buckthorn, Jetbead, Multiflora Rose, Japanese Spiraea, Narrow-Leaved & Hybrid Cattails, Black & Pale Swallow-Worts, Bush Honeysuckles, Tartarian, Amur, Oriental Bittersweet.


Japanese barberry invades a Pennsylvania forest



What can you do?

  • Be selective and research your plants prior to purchasing them.
  • Learn to identify invasive plants and look for them on your property.
  • Remove existing invasive plants and replant or seed native plants as soon as possible.