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Over 8,000 hours per year in staff and volunteer time are spent removing invasive species from Ann Arbor natural areas. As a result, many high-quality natural areas are more ecologically healthy, as well as more aesthetically-pleasing and open. Despite these positive changes, invasive species continue to impact our native ecosystems and require ongoing management.
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- Many non-native plant species were introduced to North America by European settlers for agricultural, medicinal, and ornamental purposes. The introduction of non-native organisms continues to be a problem today due to our increased travel and international trade. Not all non-native plant or animal species become problems (many non-native organisms represent significant human food sources), but some non-natives have aggressive traits that make them invasive species.
What are 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 extended growing seasons.
The City of Ann Arbor maintains an invasive species list. The list includes terrestrial species that are not native to southeast Michigan (or have non-native genotypes on the list), and meet at least one of the following criteria:
- 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 biodiversity. 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.
What is the City of Ann Arbor doing to control invasive species?
Ann Arbor Natural Area Preservation (NAP), with the help of thousands of volunteers, is working to control the spread of invasive species in local natural areas. NAP has seen great success using the following techniques, but there is much more work to do in Ann Arbor’s natural areas. Consider volunteering with NAP to help control invasive species in Ann Arbor's natural areas.
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Prescribed Ecological Burns
- Our native Ann Arbor ecosystems are fire-dependent. Until settlers began suppressing fires in the early 1700s, fire enriched the soil and removed dead thatch, allowing diverse native plant and animal communities to thrive. Continued fire suppression has disrupted the natural balance and allowed fire-intolerant, non-native plant species to out-compete the native, fire-adapted plants. Fire controls woody and non-native plants that would otherwise overtake natural areas. It stimulates native plants that are adapted to fire and helps native plants regain their competitive edge. NAP has had success controlling buckthorn, honeysuckle, dame’s rocket, and garlic mustard through prescribed burning.
Manual Removal
For some invasive plants, manual removal is the most effective management tool. For example, garlic mustard, an herb that invades deciduous forest and displaces native wildflowers, has been reduced in Ann Arbor natural areas primarily due to coordinated garlic mustard pulling events. Each spring, NAP hosts its annual Garlic Mustard Weed-Out Day, a coordinated effort to get volunteers pulling garlic mustard in natural areas throughout the City. This and other work days result in the removal of several thousand pounds of garlic mustard from Ann Arbor's natural areas. Manual removal is also used to clear buckthorn and honeysuckle from the forest understory.
Targeted Herbicide Applications
Licensed staff use herbicide to control some invasive plants, usually in combination with other control methods. For example, treating buckthorn and honeysuckle stumps with herbicide after cutting and manually removing the majority of the plant targets the root system and reduces plant regrowth. NAP staff also use herbicide to treat purple loosestrife, a wetland invasive plant.
More information
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Find out how YOU can help improve the State of Our Environment.
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Last Updated August 2009