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

The invading aquatic plant, Myriophyllum spicatum L. is a management concern in many North American lakes because it replaces native species and because its dense growth can be a nuisance to lake users. It is common for M. spicatum to expand quickly upon reaching a lake, remain the most abundant littoral plant for a number of years, and then decline rather rapidly. This pattern held true for Lake Wingra, Dane County, WI, where M. spicatum dominated the littoral vegetation during the late 1960s, but abruptly declined during the 1970s. In this paper, we explore the changes in the Lake Wingra plant community that have occurred in the wake of the M. spicatum decline. We present results of 1991 and 1992 vegetation surveys indicating that M. spicatum, while no longer the dominant macrophyte, remains an important member of the Lake Wingra plant community. It and Ceratophyllum demersum L. now make up roughly equal parts of the littoral vegetation, and native species, rare or absent during the I960s, are growing well. By comparing current plant 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 two decades while the native vegetation has expanded.