Plant communities are groups of plant species that naturally grow together in one location, sharing the same habitat needs and sometimes depending on one another for survival. At the Arboretum, these communities changed over time. The first settlers saw vast grasslands with only a few trees, because fires regularly burned back prairie grass and kept trees from growing. As more people moved into the area, trees were planted, prairie was converted to farm fields, and the fires ended. Trees then spread from the river bank, transforming the area into the mix of habitats found at the Arboretum today, including river floodplain, oak savanna, prairie, and woodlands. Within the grounds of the Mary Jo Wegner Arboretum and the Perry Nature Area stands one of the largest documented bur oaks in South Dakota, a historic tree located north of this garden.