ASPECTS OF THE ECOLOGY OF AN INVASIVE PLANT, GARLIC-MUSTARD (ALLIARIA-PETIOLATA), IN CENTRAL ILLINOIS

Alliaria petiolata (garlic mustard), an exotic plant species, has inva ded woodlands in several areas in mid-western and northeastern United States and adjacent Canada, and it is displacing the indigenous under- story flora. This study was conducted to provide information about the species' biology that might be useful in controlling its spread in na tive woodlands. The plant is a strict biennial in North America, spend ing the first year of growth as a basal rosette. This period of relati vely slow growth is followed by a period of rapid shoot elongation (1. 9 cm/day) during early spring of the second growing season. The plant is capable of cross- and self-pollination, although pollination and st igma receptivity occur before the flower is open, so autogamy is the m ost likely breeding system. Garlic mustard invests 20.4% of its biomas s in reproductive effort, with an annual seed rain of 15,000 seeds/m(2 ). Seed dispersal from fruits begins in early July and continues into October. Most seeds germinate in the spring following the year in whic h they were produced. Seedling recruitment is high (8.3-18.0 seedlings /dm(2)), but only about 7.5% of the plants survive to maturity. The su ccess of the plant in invading woodlands appears to be related to (1) its autogamous breeding system that allows a single individual, or a f ew individuals, to establish populations of genetically similar but in terfertile individuals; (2) high seed production, permitting establish ment of large numbers of individuals; and (3) rapid growth during the second growing season, which increases its competitive ability. Becaus e of garlic mustard's ability to occupy understory habitats successful ly, it may be unrealistic to expect to eliminate the plant from many h abitats it has already invaded.