When the first Europeans arrived in the Midwest, oak savannas dominated much of the southern half of Wisconsin, covering an estimated 5.5 million acres.
Today, far less than one-percent of the savanna remains, and nearly all of that is badly degraded. At most, only a few thousand acres is healthy savanna.
Here in the Conservancy, Frederick’s Hill is an excellent example of a remnant oak savanna undergoing restoration.
Since the late 1990s, hundreds of volunteers have removed invasives, assisted in prescribed burning, and collected and scattered seeds.
The battle against invasives continues, but progress is evident. Notice the openness of the bur oak canopy and the diverse understory.
Learn more about oak savannas and restoration by volunteering for a work party with the Friends.
Savannas are characterized by scattered trees and shrubs with nearly continuous ground cover of grasses, sedges and broad-leaved plants.
Actual tree cover varies depending on how recently and how intensely a savanna was burned. Extremely hot fires can nearly eliminate tree cover for many years; 20 years without fire can result in savannas overgrown by trees. A major reason why so few healthy savannas remain is a result of fire suppression.
Where tall-grass prairie and savanna mingled, such as this area, bur oak was often the only tree that could survive frequent high-intensity fires. Even when fires kill off the above-ground growth of smaller bur oaks, the root system will usually resprout as multiple stems or oak grubs.
With European settlement, most of the savannas were cleared for cultivation or pastured.
With an increasingly fragmented landscape and efforts to eliminate wildfire, most remaining savannas succeeded into woodlands with brushy undergrowth.
Because they provide attractive suburban home sites, many surviving savannas are further compromised by expansive lawns and non-native ornamental plantings.
Many efforts are underway to rescue remnants from further degradation by removing invasive vegetation, seeding appropriate savanna species and introducing prescribed fire.
Oak savanna restoration also can help protect a number of endangered animal and plant species, such as giant yellow hyssop, purple milkweed and cream gentian.