Plants Out of Place

Removing Invasives

In various ways we bring species from other parts of the world into our native woodlands and prairies. Often these are attractive landscaping escapes. These introduced plants can have devastating effects on native ecosystems. To be sure, many introduced species pose no problem. Dandelions, the bane of many homeowners, are weaklings when it comes to competing in healthy native communities. Of the 900 or so introduced plant species in our area, only a fraction are capable of invading our natural areas and replacing native species. That fraction, however, can severely damage the integrity of the system.

European buckthorn is one of the most damaging invasives. Originally introduced as a hedge, it produces large quantities of juicy black seed-bearing berries. Birds eat the berries, then fly into nearby forest preserves where their droppings “plant” the seeds. Buckthorn grows into dense shade-producing thickets, killing off sun-loving native grasses and wildflowers. It is so aggressive it is 5 times more abundant than the next most common tree in the Chicago region.*

Using handsaws, volunteers cut and remove the buckthorn, letting the sunlight reach the woodland floor once again. Cut stumps are carefully dabbed with Garlon, a low-toxicity herbicide that travels into the buckthorn roots, killing the plant. Without herbicide, buckthorn resprouts vigorously. The best time to remove buckthorn is in the cold season when other plants are dormant.

Garlic mustard is another vigorous invasive plant that can displace a wide number of native plants in a short amount of time. Its an herbaceous plant that is pulled in spring and summer.

Purple loosestrife invades wetlands, choking out other vegetation and diminishing the quality of habitat that sustains wetland animals.

*according to a 2010 report by the USDA Forest Service, European buckthorn overwhelmingly leads at 28.2 percent, with the next most common tree being green ash (5.5 percent).

Some of the worst

Garlic Mustard is said to have come to our continent with the European settlers, who used it as a potherb in their cooking. It’s a biennial, growing as a first-year rosette that over-winters and then sends up a flowering stalk the second year. After producing many seeds, the parent plant dies. Its offspring begin the cycle again, and the colony rapidly expands, pushing out the native wildflowers.

Purple Loosestrife is beautiful but deadly to our native wetlands. Each plant produces thousands of seeds, which are carried downstream to produce new populations. Eventually, the native plants are choked out and what remains is a monoculture that supports far fewer insects and other animals.

European buckthorn affects the woodlands in many ways. Its dense shade robs other plants of sunlight needed to survive. The resulting bare soil areas are prone to erosion. Buckthorn also releases a chemical in the soil that inhibits the growth of oaks and other hardwood trees. Lack of oak reproduction is a major challenge to the restoration of our woodland, where oaks are a dominant tree in the canopy.