I Prevalence and Importance of Regime Shifts

A Tale of a Lake More than 15,000 years ago, glaciers advancing from the northeast gouged a basin of more than 200 km near what is now Madison, Wisconsin, USA. The ice was more than 300 m thick. A considerable amount of water flowed over the land as the glaciers melted, about 12,000 years ago. This water filled much of the basin, which became the watershed of what is now the Madison Lakes (Fig. 1). Wooly mammoths roamed the shoreline, and giant beavers were active in the extensive shallows and wetlands surrounding the lake. Gradually the water receded until the five lakes of the present day were distinguishable. By about 10,000 years ago, Lake Mendota, the largest of the Madison lakes, was identifiable, although it stood more than 2 m above the present-day lake level and was perhaps two or three times larger in area than in 2002. Extensive wetlands spread northward from the lake. Other plant species migrated into the area as the glaciers receded northward. Eventually forests of maple, red oak and basswood cloaked the southern shores of Lake Mendota, while oak savannas and prairies were found in the uplands of the lake’s watershed.