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Invasive Ornamental Plants Pose Threat for Native Wildlife

Callery Pear infestation in a natural area (Photo from Bugwood Wiki, University of Georgia)

Callery Pear infestation in a natural area (Photo from Bugwood Wiki, University of Georgia)

In winter we dream of spring. We peruse garden catalogs for beautiful plants to adorn our homes. When late spring arrives and the danger of frost has passed we happily shop at local box stores and nurseries and put our treasures in the ground. Unfortunately, many of those treasures are not native to the northeastern Illinois region or the United States. In fact, some ornamental plants have escaped into natural areas and become problematic.

In many cases invasive ornamental plants will leaf out early in the spring and grow rapidly in height, shading out native plants. Some invasive ornamentals release chemicals into the soil that inhibit the growth of plants around them. When invasive ornamental plants outcompete native plants many of the organisms (butterflies, birds, mammals) that relied on those native plants for food and shelter are left to find new resources.

Some ornamental plants spread via roots, some produce thousands or even millions of seeds that are carried by wind, water, fur, clothing, and shoes; and some have fruits that are eaten by birds or mammals and are dispersed far from their source plant. Escapees include very popular plants: Japanese barberry – red and purple variety (Berberis thunbergii), Burning bush (Euonymous elatus), Silvergrass (Miscanthus spp.), and the ubiquitous Callery Pear (Pyrus calleryana).

Callery or Bradford Pear is an invasive ornamental plant (non-sterile cultivar) that is native to Southeast Asia and is used to beautify roadsides, parking lots, and residential areas in the Midwest, East, and South. Certain birds eat its fruits and then transport seeds to natural areas where the trees become established. Populations outside of intended plantings/gardens have been documented at Midewin National Tallgrass Prairie and Morton Arboretum.

The tree can grow up to 50 feet high and 30 feet wide and has a teardrop shape. Its leaves are alternate, simple, and shiny with wavy, slightly toothed edges. In early spring it produces lovely five-petalled white flowers (1 inch diameter) and in summer small green to brown fruits (about 1.2 inch across) can be found among its branches. Its branches are very susceptible to wind and ice damage because they grow at acute angles to an expanding trunk. The distribution map for this species is posted at http://www.eddmaps.org/distribution/usstate.cfm?sub=10957. Additional information about this species can be found at http://niipp.net/?page_id=530&id=PYCA80.

The plant species mentioned are only a few of the potentially problematic ornamentals in northeast Illinois. More information about these species and suggestions for native alternatives can be found at the Midwest Invasive Plant Network website http://mipn.org/MIPN%20redraft2.pdf, the Chicago Botanic Garden website http://www.chicagobotanic.org/research/conservation/invasive/chicago/, and Conserve Lake County’s Conservation@Home website http://www.conservelakecounty.org/conservationhome/welcome-to-eco-friendly-landscaping. Please consider purchasing native plants the next time you are buying plants for your garden. The native plants, butterflies, and birds will thank you.

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