Patterns of vegetation change in Lake Wingra following a Myriophyllum spicatum decline.
The invading aquatic plant, M. spicatum, is a management concern in many North Americans 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 Country, Wisconsin, where M. spicatum dominated the littoral vegetation during the late 1960s, but abruptly declined during the 1970s. The changes in the Lake Wingra plant community that have occured in the wake of the M. spicatum decline were investigated. Results of 1991 and 1992 vegetation surveys are presented, indicating that M. spicatum, while no longer the dominant macrophyte, remained an important member of the Lake Wingra plant community. M. spicatum and Ceratophyllum demersum now make up approximately equal parts of the littoral vegetation, and native species, rare or absent during the 1960s, are growing well. By comparing current plant distributions with those found earlier, probable causes for the M. spicatum decline were examined; no single factor seemed to be responsible. The M. spicatum decline in Lake Wingra has been sustained over roughly two decades while the native vegetation has expanded.