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Over 8000 hours per year in staff and volunteer time are spent removing invasive species from the parks. This has resulted in many high-quality natural areas being effectively considered “weed-free,” more aesthetically-pleasing and open, and suitable for nature observation. Despite these positive changes, invasive species continue to threaten the balance in many natural areas.
Source: Ann Arbor Natural Area Preservation |
In North America, many non-native plants were brought over from other continents by European settlers. Plants were brought over for agricultural, medicinal, and ornamental purposes. Many plants are introduced accidentally as well. The introduction of non-native organisms continues to be a problem today due to our increased travel and international trade. Not all non-natives plants or animals become a problem. Many non-native plants represent significant human food sources. However, some of these plants have certain aggressive traits that make them invasive species.
What is an invasive species?
Invasive species are those non-native species that can significantly disrupt natural communities causing environmental or economic harm. In a new environment, invasive plants are released from the natural constraints of their native ranges. They lack the control of herbivores, parasites, diseases, and competition that was present in their native habitats. Invasive plants exhibit both rapid growth and reproduction rates because of abundant seed production, reproduction through vegetative clones, and /or extended growing seasons .
The species on the Ann Arbor invasive species list are not native to southeast Michigan (or have non-native genotypes on the list) and are non-aquatic species. The criteria used for the list are:
- Demonstrated invaders in Ann Arbor 's natural areas or wetland mitigation areas, or
- Documented invaders in neighboring states, and hardy in zones 3b – 6a, or
- Ornamental plant species that escape readily, or
- Large weedy species that would be undesirable in a non-turf lawn
How do invasive species affect the environment?
Because invasive plants have a distinct advantage over native plants, there is a decline in native plants as well as overall diversity. The decline of native plant populations triggers a decline in populations of animals dependent on native plants for food or shelter. The impact ripples through the food web, ultimately decreasing local species diversity in plant and animal communities and disrupting remnant native ecosystems. Invasive animal species are also cause for concern.
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