The term ‘alien’ is used to describe an invasive species that is non-native to the ecosystem of the area, which can cause environmental harm or even pose a human health risk. These species often spread quickly and are difficult to remove because of how quickly they reproduce with no natural predators or competitors in these areas.
Often, these invasive species are brought to new areas by humans who do not realize that these plants are destructive. For example, this can happen when people plant garden ornamentals or bring in forage plants for cattle. It can also happen when species are accidentally imported with other nursery stock, fruits, or carried on vehicles, in packaging, and shipping containers.
Chicago’s natural areas provide habitat for more than 400 species of mammals, birds, reptiles, amphibians, and fish. Today, these important natural areas and the wildlife that depend on them are threatened by the spread of invasive species. Invasive species alter the local ecology and out-compete native species for resources. So it’s crucial to reduce the threat of invasive plants in our region.
Below is a list of trees to be on the lookout for, the list includes links to help you identify each alien species:
- Tree-of-heaven Ailanthus altissima
- Mimosa Albizia julibrissin
- Autumn olive Elaeagnus umbellata
- Glossy buckthorn Berberis thunbergii
- Amur honeysuckle Lonicera tatarica
- Callery pear (Bradford pear) Pyrus calleryana
- Princesstree Paulownia tomentosa
- European buckthorn (common buckthorn) Rhamnus cathartica
- Black locust Euonymus alatus (Thunb.) Sieb.
- Chinese privet Ligustrum sinense Lour.
