Farther to the north, where strings of kettle lakes and steep moraines created fire barriers, sugar maple-basswood forests were largely unbroken on the landscape, except where conifer swamps occupied small wetlands. Fire in areas dominated by oak savannas and forests. Heavy development and recreational pressures threaten. Lulu Lake Preserve. Kettle Moraine State Forest.
Several preserves protect fens, prairies, and adjacent oak-dominated upland areas.
Recreational and residential development around the numerous kettle lakes may severely limit natural area management and expansion of natural areas in many areas. The Kettle moraine is considered a critical landscape for many uncommon or rare species characteristic of southern Wisconsin, especially vertebrates, but also invertebrates, plants, and aquatic organisms. This is the most intact landscape in southeastern Wisconsin.