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Lake County Forest Preserves | Preservation, Restoration, Education and Recreation


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Managing Invasive Species

Invasive species are plants and animals that spread aggressively. These are often non-native species that overtake habitats, reducing the overall biological diversity and causing ecological damage to our native communities. This happens because natural enemies such as predators, disease or competitors that control these species are left behind in native lands.

Non-native invasive species are the biggest threats to habitat after fragmentation. Invasive woody species are controlled by mechanical removal, or by periodic controlled burns. Some invasive species, such as emerald ash borer, create unique challenges that require the cooperation of local and regional agencies to minimize the spread and reduce the damage of infestation.

The first phase of restoration in the preserves typically involves removal of non-native, invasive plants by our crews, contractors and volunteers. The widespread clearing of invasive species improves conditions for controlled burns, reduces competition for native trees and shrubs, and increases light levels.

Invasive Insects

Asian Long-Horned Beetle

Thousands of hardwood trees have been lost to the Asian long-horned beetle. The best line of defense against this devastating invasive species is you. Learn more »

Emerald Ash Borer

This non-native invasive beetle has killed tens of millions of ash trees in the northeastern United States and Canada since its discovery. Learn more »

Invasive Plants

Buckthorn and other Woody Invasives

Woody plants include long-lived trees, shrubs and vines. As part of the continuing restoration and management of the forest preserves, we selectively remove invasive woody vegetation. Learn more »

Non-native invasive species, such as buckthorn and honeysuckle, are removed to restore ecological health, function and sustainability. Our Small Invasive Tree & Shrub (SITS) program treats selected areas in woodland restoration sites by hiring contractors to control small, invasive trees and shrubs. SITS strives to:

  • Eradicate invasive tree and shrub species from high quality woodlands, including nature preserve sites.
  • Treat approximately 200 acres of woodlands each year.
  • Test the efficacy of treatment methods alone and in combination with other adaptive management strategies.

These efforts have increased the amount of sunlight reaching native ground-layer plants, incresed the diversity of herbaceous plants, reduced soil erosion and improved the overall health of the targeted ecological communities.

Garlic Mustard and other Herbaceous Invasives

Herbaceous plants are those whose stems die back during the year, following seed production or by late fall. Preventing seed dispersal is crucial for controlling these invasives.

Control can be achieved by a variety of manual, mechanical, chemical and biological methods. Garlic mustard is an herbaceous biennial that invades wooded areas throughout the eastern United States. Once introduced, it can form dense stands that shade and compete with native ground-layer plants. Garlic mustard is best controlled by pulling the young plants up by the roots in early spring before the seeds form.

Eurasian Water-Milfoil and other Aquatic Invasives

Eurasian water-milfoil is a non-native submerged aquatic plant. Its ability to surive over winter, grow rapidly in spring and reduce sunlight available to native aquatic plants often causes its total domination of an area. Learn more »

Infestations of this and other aquatic invasive species threaten native aquatic communities by disrupting the predator-prey relationships, impairing the ability of fish to spawn and reuding the number of nutrient-rich native plants that provide food for waterfowl. Dense mats also reduce water quality and affect recreational opportunities and aesthetics of lakes, rivers and streams.

Ornamental Invasive Plants

People ahve introduced the vast majority of invasive species, either accidentally or deliberately. Some ornamental plants have escaped landscaping and invaded our natural areas. Planting native alternatives saves time, water and enhances the local ecosystem.

Aquatic Nuisance Wildlife

Zebra Mussel

Zebra mussels were introduced to North America when seagoing ships dumped ballast water containing their larvae in Great Lakes ports. Their presence threatens the survival or native mussels, fish and invertebrates. Learn more »

Zebra mussels reproduce quickly and have fewer predators than in their native home of Europe Asia. A single zebra mussel can produce up to a million eggs each year. They can take over aquatic communities by filtering huge amounts of water, which removes the algae and plankton that is the key food source of many native species.

Asian Carp

There are seven carp species that were introduced to the United States from Asia. The term "Asian carp" refers to four speices: black carp, bighead carp, grass carp and silver carp. Learn more »

The diet of Asian carp overlaps the diet of many native fish in Illinois Rivers and lakes. Therefore, these invasive carp are stripping the key source of food for native fish. In some areas, the Asian carp now make up more than 95% of the biomass. As the Asian carp continue to spread north, the Great Lakes are now at risk.

Pathogens and diseases

Ticks and Lyme Disease

While enjoying outdoor activities, it is important to take action to prevent bites from ticks that share our spaces. Learn more »

West Nile Virus

This virus is most commonly transmitted to humans by mosquitoes. Our challenge in working with west nile virus, along with many other issues that we face, is finding the right balance that benefits and provides safeguards for both people and nature. Learn more »


Each and every person can make a difference. There are many resources and opportunities available to stop the spread of invasive species in Lake County.


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