PATTERNS OF VEGETATION CHANGE IN LAKE WINGRA FOLLOWING A MYRIOPHYLLUM-SPICATUM DECLINE

The invading aquatic plant, Myriophyllum spicatum L. is a management c oncern in many North American lakes because it replaces native species and because its dense growth can be a nuisance to lake users. It is c ommon for M. spicatum to expand quickly upon reaching a lake, remain t he most abundant littoral plant for a number of years, and then declin e rather rapidly. This pattern held true for Lake Wingra, Dane County, WI, where M. spicatum dominated the littoral vegetation during the la te 1960s, but abruptly declined during the 1970s. In this paper, we ex plore the changes in the Lake Wingra plant community that have occurre d in the wake of the M. spicatum decline. We present results of 1991 a nd 1992 vegetation surveys indicating that M. spicatum, while no longe r the dominant macrophyte, remains an important member of the Lake Win gra plant community. It and Ceratophyllum demersum L. now make up roug hly equal parts of the littoral vegetation, and native species, rare o r absent during the I960s, are growing well. By comparing current plan t distributions with those found earlier, we examined probable causes for the M. spicatum decline; no single factor seemed to be responsible . The milfoil decline in Lake Wingra has been sustained over roughly t wo decades while the native vegetation has expanded.