A savanna community is sort of a transition between a forest and a prairie. In fact, savannas naturally occur wherever forest and prairie meet.
In a savanna there will typically be a few scattered trees or groves of trees, typically bur oak (Quercus macrocarpa) or northern pin oak (Quercus ellipsoidalis) or quaking aspen (Populus tremuloides) interspersed with prairie plants.
Savannas are typically maintained by periodic wildfires. Native savannas have nearly all been converted to agriculture or have grown into forests following the cessation of wildfires.
Habitats in Minnesota that look like savannas are invariably cattle pastures that contain a few open grown trees, but lack native prairie plants.