Plants don't live by themselves. They are always part of a community of plants and associated animals. Knowing the different natural communities is an essential part of ecological understanding.
THE IDEA OF A "NATURAL COMMUNITY"
MAJOR NATURAL COMMUNITIES IN WISCONSIN
If you like being thorough, here is a list of all the natural communities of Wisconsin with websites for each.
NATURAL COMMUNITIES OF WISCONSIN: RESOURCES
Curtis, John T. The Vegetation of Wisconsin : An Ordination of Plant Communities . Madison : University of Wisconsin Press, 1959. (book)
Hoffman, Randy. Wisconsin Natural Communities: How to Recognize Them, Where to Find Them . Madison , WI : University of Wisconsin Press, 2002. (book)
Umbanhowar, C.E., Jr. "Vegetation of Wisconsin Habitats." Wisconsin Botanical Information System (Wisconsin State Herbarium).
NATURAL COMMUNITIES IN OTHER STATES