Targeting Invasive Species

By Tom Koritansky, Natural Resource Manager

Natural areas in the parks are home to many varieties of plants and animals. Some organisms are rare and unique, living only in very distinct habitats under special conditions while others are more commonly found and can live under broader surroundings. Plants and animals living in their native ranges have evolved with many checks and balances that keep their populations under control and adaptations to help them survive and reproduce under various constraints. Sometimes though, when they are removed from their natural settings there can be unintended consequences.

Emerald ash borer

Organisms that are found outside of their native ranges that cause some kind of harm to the environment where they have been introduced are called invasive species. These organisms can be plants, animals and even pathogens. The problems they cause are wide ranging and can be harmful to the environment. For example, an invasion of purple loosestrife can degrade a wetland over time and cause the area to be unsuitable habitat for native plants and animals. An invasion of the brown marmorated stinkbug causes damage to fruit and vegetable crops negatively affecting the economy. 

Purple loosestrife is noted by its showy purple flowers. It is an aggressive invasive plant, especially in wetlands and stream banks. 

Invasive species are introduced to new environments by a number of pathways and vectors. Some were intentionally introduced like multiflora rose that was once used for wildlife cover and reed canary grass that aided in erosion control. Others were introduced for their ornamental value like bush honeysuckle. Sometimes their introduction was accidental—arriving either as contaminants in freight, wood or hitchhikers on plants and food products. One notable invasive species, emerald ash borer, arrived to North America this way and quickly spread.

Bush honeysuckle fuits are less nutritious for wildlife than the fruits of native shrubs. 

Not every introduced species becomes invasive. Some species new to an area are not adapted and do not survive, while some others become naturalized in their new environment and do not really cause any harm. Only a small number of introduced species become invasive, and it is hard to predict which ones will and which ones will not. Some invasive species spread quickly, while others take more time. Potential invasive species are able to spread quickly since they can grow and reproduce in their new setting without much competition or anything else to keep their population in balance.

Asiatic bittersweet is a vine that forms dense mats in forest canopies that shade vegetation growing below. 

Lake Metroparks strives to curtail the spread of invasive species in order to protect biodiversity within the parks. Most efforts involve controlling invasive plant populations that spread quickly once established and degrade natural areas. The spread of invasive plants leads to less suitable habitat for wildlife. For example, fruit from invasive species such as honeysuckle are of low nutritional value for wildlife compared to native shrubs. Populations of rare and uncommon plants suffer most since they already are found in small numbers and can be quickly overtaken and displaced by invasive plants.  

Lake Metroparks’ natural resource crews use a variety of methods to control these ecological aliens. Some plants like garlic mustard, a problematic species that outcompetes native spring wildflowers, can be easily pulled out of the ground. Sometimes mechanical options like cutting and mowing are used. Cutting works especially well for species of vines like Asiatic bittersweet that form dense mats in the forest canopy, weaken trees and shade vegetation growing below. Herbicides are also helpful in controlling aggressive plants like phragmites that often overtake ponds and wetlands. Timing applications and monitoring weather conditions are important when using herbicides so that control is most effective.  

Garlic mustard can quickly outcompete forest-growing spring wildflowers.

One example of the difference invasive species control can make can be seen at one the most unique habitats in Lake County: the estuary at Arcola Creek Park. At one time, the estuary was densely populated with invasive reed canary grass, narrow-leaf cattail and purple loosestrife. Now, after many years of hard work, it has once again become a rich habitat of native plants complete with different species of burr-reed, rushes and sedges among others. Wildlife in the estuary is once again thriving—marsh birds are returning to nest and new singing insects were documented last year. Even though controlling invasive species can be arduous and frustrating at times, when successful, the results are worth all the effort.

After many years of invasive species control efforts, native plants like burr-reed, rushes and sedges have returned to Arcola Creek.