An oak savanna is an open, grassy space at the edge of a forest with a few scattered trees, formed where prairie transitions into forest. Oak savannas are an important part of the landscape because their plants provide food and habitat for animals and insects, and oak trees help keep the planet healthy by removing carbon dioxide from the air and providing shade and oxygen. Before settlers came, there were 50,000,000 acres of oak savannas in the Midwest, but only 30,000 acres remain here, less than 1 percent, making them more endangered than the rainforest. Protecting them is important because they could disappear. Periodic disturbances such as wildfires benefit oak savannas by clearing invasive plant species, renewing the soil, and causing some plants to drop their seeds, bringing new life to the forest. Within this habitat, a snag tree is dead but still used for perches and nests, a den tree is large enough for an animal to make a home, and a mast tree produces fruit or nuts such as acorns for animals to eat. Oak savannas are home to unique wildlife including white-tailed deer, gray squirrel, red squirrel, turkey vulture, raccoon, wild turkey, karner blue butterfly, and red-headed woodpecker, and the endangered karner blue butterfly depends on wild lupine found there.