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Responding to Invasive Species in Pennsylvania’s State Forests

February 28, 2020 12:00 AM

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Invasive plants can significantly alter our forested landscapes, negatively impacting plants, animals, their habitats, and the natural processes of which they are a part.

Left unchecked, they can take over and dominate entire areas. Worse, invasive plants can alter soil chemistry and local ecosystems -- setting the stage for other invasive species to follow.

Invasive Species Bring More Invasive Species

Close Up of Tree of Heaven.jpg

Tree-of-heaven is an extremely aggressive invasive tree. It doesn’t take long for landscapes to transition from one or two stems to thousands.

Tree-of-heaven releases chemicals into the soil that inhibit the growth of native plants, which tends to encourage other exotic species that evolved with it overseas.

For this reason, areas overgrown with tree-of-heaven frequently also have infestations of barberry, Japanese stiltgrass, multiflora rose, and Asiatic bittersweet.

As native acreage is lost, native animals that feed on plants concentrate their feeding into smaller areas of leftover native plant communities, inflicting unbalanced harm.

Sustained overgrazing often kills native plants, opening more sites for invasive species to populate, accelerating the ecological damage.

Invasive Species on Michaux State Forest

Invasive Infestation in Michaux Tree of Heaven.jpg
Tree-of-heaven infestation in Michaux State Forest

Invasive plants are a major problem in Michaux State Forest. Common invasive plants there include:

  • Mile-a-minute
  • Tree-of-heaven
  • Japanese angelica tree
  • Japanese barberry
  • Autumn olive
  • Japanese privet
  • Japanese stiltgrass
  • Multiflora rose
  • Japanese knotweed
  • Poison hemlock

Many of these invaders arrived by illegal dumping of yard waste, which often contains seeds and viable roots and shoots of invasive species.

Aggressive Response

Spraying Japanese barberry in Michaux State Forest

Infestations of invasive species are taken very seriously. DCNR’s Bureau of Forestry uses an “early detection rapid response” protocol whenever a new invasive is found, which usually destroys the invasive species before it becomes a problem.

Due to the sheer number of acres the bureau manages, it is impossible to notice all outbreaks -- leading to unintended infestations.

Such was the case for a 400-acre Japanese barberry infestation near Pine Grove Furnace State Park.

The Bureau of Forestry utilized an herbicide treatment program for several years in the area, essentially eradicating the unwanted invasive.

Follow-up spot treatments are routine, and the area will eventually be replanted with native species.

Get Help If Necessary

Weevil on mile-a-minute plant

The invasive plant problem can be daunting, even for our hard-working foresters.

Sometimes it is necessary to call in reinforcements – like, in 2016, when Michaux staff used contractors to eliminate a 95-acre stand of cork and bee-bee trees near Mont Alto.

Staff continue to work on a management plan to treat an additional 202 acres in this region.

The Bureau of Forestry also uses “biological controls,” releasing plant-eating weevils to control the mile-a-minute weed.

These insects have been shown to target the invasive weeds, while avoiding native plants. 

Although the weevil will not eradicate mile-a-minute weed, it does have the ability to control its spread.

Keeping Up the Fight

Volunteers help remove invasive Japanese knotweed

Part of DCNR’s mission is to conserve native wild plants. In order to achieve this goal, control of invasive species is crucial, and we hope Pennsylvania citizens will help us in this fight.

Things You Can Do

  • Plant only native plants at home and encourage others to do the same
  • Eliminate invasive species in your landscape
  • Never transfer yard waste to new locations
  • Participate with local conservation groups to do invasive species “roundups”

Learn more about invasive species and native plants of Pennsylvania at DCNR’s website.

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