Walking through one of the Hancock Parks you might have noticed areas with lots of trees and shrubs removed and thought to yourself, “What happened? Why would the park district remove all these plants that provide food and shelter to the local wildlife?” It is understandable to have these questions because it seems counterproductive to the idea of a park. After all, isn’t one purpose of a park district to provide an area that people can reconnect with nature?
The answer is habitat restoration. The next logical question would be what is the area being restored to? The goal of habitat restoration is to return ecosystems (woodlands, prairies, wetlands) to a more native and natural state. The trees and shrubs being removed are labeled invasive species because they are not naturally found in the area and will have many detrimental side effects if left unchecked.
What is a non-native plant and why is there a cause for alarm? A non-native plant is simply a plant that is not originally from a given area. For example, the dandelion that is growing in just about every yard is a non-native plant because it is originally from Europe and Asia and was brought over to North America. One of the goals of habitat restoration is to remove non-native plants and replace them with native plants. Native plants are plant species that have long been found in our area and occur naturally throughout the park district.
Why are non-natives so bad and why are we trying to remove them from the park district? Green does not necessarily mean good when it comes to plants. Most non-native plants are aggressive and out compete the native plants which in turn affects native wildlife. Having a large diversity of native plants is important because it provides food throughout the year to many animal species. Spring wildflowers such a Spring Beauty (Claytonia virginica) bloom early in the year which provides a food source for many pollinators. A woodlot with many types of trees is more beneficial to wildlife because seeds mature at different times of the year. This provides a food source year-round and not just during a short window.
Blue Rock Nature Preserve is currently experiencing some major habitat restoration. Prior to the start of the habitat restoration project, Bush Honeysuckle (Lonicera spp.) and Tree-of-heaven (Ailanthus altissima) dominated the preserve. Due to the sheer number of non-native plants this restoration is going to be a continuous project. The first step is aggressive removal of the honeysuckle. This is done by cutting the plants near ground level and applying herbicide to the stumps. Treating the stumps is important to prevent resprouting. Tree-of-heaven was treated by using herbicide in a hack and squirt method. This method allows the tree to transport the herbicide throughout the root system and to any offshoots of the tree, as tree-of-heaven is colonial in nature. One of the reasons these species are so invasive is because of the large number of seeds produced yearly. Tree-of-heaven can produce over 30,000 seeds a year and these seeds can remain viable for years in the soil. Removal of both bush honeysuckle and Tree-of-heaven is important because they are both allelopathic. Allelopathic means that these plants are capable of producing biochemicals in the root systems that inhibit growth of other plants, acting like a natural herbicide. The chemicals weaken other plants in the area allowing the invasive seedlings to become established. Treatment of these newly emerged seedlings consists of foliar herbicide being sprayed late in the fall. We apply foliar herbicide late in the fall due to the fact that honeysuckle retains it leaves well after native plants have gone dormant for the year. Applying in the fall is also effective because plants are taking all nutrients to the root systems along with the herbicide, which in turn kills the plant.
After removing both the large bushes and new saplings we are starting to enhance the plant biodiversity. Native hardwood trees such as white oak, red oak, black walnut, sugar maple, black cherry, and eastern redbud have been planted throughout the park. Because of the dense growth of honeysuckle, native ground cover was lacking. To remedy this, we spread native woodland wildflower seeds all around Blue Rock.
Common Invasive Plants
- Amur, Tartarian, and Morrow Honeysuckle, collectively known as bush honeysuckle (Lonicera), are probably our most common and widespread invasive species. These species are usually first to leaf out in the spring and last to drop their leaves in the fall allowing for rapid growth every year. Because of the early leave development, forest floors are shaded preventing native spring wildflowers who need the sunlight to bloom.
- Garlic mustard (Alliaria petiolate) is an herbaceous plant found throughout the parks. This 2-to-4-foot plant has small white flowers that produce up to 1,000 seeds a year with seeds remaining viable for 7 years in the soil. This combined with the fact that garlic mustard is one of the first plants to begin growing in the spring, allows dense stands of this species to fill any available space.
- Dame’s rocket (Hesperis matronalis) is an attractive purplish biennial flower ranging from 2-to-4feet tall. While the flower itself may look pretty and beneficial to local pollinators, the prolific seed rate (20,000 seeds per plant) will quickly lead to nothing but Dame’s rocket in the area.
- Tree-of-heaven (Ailanthus altissima) is often found in disturbed areas and can quickly dominate an area. Capable of growing up to seven feet a year, saplings easily outcompete slower growing native trees for light and nutrients. Colonial in nature, a single tree can send out hundreds of root suckers quickly leading to large numbers of new trees. This tree is also capable of producing over 30,000 wind dispersed seeds each year.
- Autumn Olive (Elaeagnus umbellata) is an aggressive shrub that due to nitrogen fixing root nodules, can grow in even poor soils. Fast growing and capable of producing numerous berries, this species quickly alters the ecosystem by forming dense stands.
- Callery Pear (Pyrus calleryana) is quickly becoming a big issue in the parks and surrounding area. This popular landscaping tree is often planted in residential areas because of the showy white flowers in the spring and quick growth. Each fall, hundreds if not thousands of fruits are produced and are quickly spread to other areas by birds.
Controlling non-native plants is crucial to a healthy ecosystem and can be done in a variety of ways.
Mechanical – For small plants hand pulling is a viable option. When doing so, it is important to remove the whole plant including all parts of the root system. For larger or high density of invasive plants where hand pulling is not an option, cutting and mowing can be used. This option often requires follow up treatment in the form of cutting root suckers or repeat mowing.
Chemical – Treating invasive species with herbicide is crucial to helping control the spread. If honeysuckle and tree of heaven are cut down without treating with a type of herbicide, resprouting will occur. Due to the large quantities of seeds produced by many of these species, foliar application is the only reasonable way to maintain control of a situation. Care should be taken to prevent native species from being affected. This can be done by spraying late into the fall as most non-natives retain their leaves longer than native species.
Prescribed burn – Conducting a prescribed burn on certain habitats can help control invasive species. Many of these non-native invasive species do not have a deep root system and when a fire moves across the surface, the heat will kill the plant. This does not harm many native species because most have deep roots that are unaffected by the fire and are able to produce new growth.