Prior to Euro-American settlement, the landscapes of the upper Midwest (and much of California, the Southwest, and the Northeast) consisted of a diverse savanna mosaic of prairie, woodland, marsh, lake, and river ecosystems. The plant and animal communities of these landscapes evolved together with humans since the glacier melted 12,000 years ago.
Instead of describing the savanna as a plant community, ecosystem, or landscape, I am beginning to use the term savanna mosaic. Most academic literature on the Midwestern savanna focuses on plant communities – their origins, distribution, and species composition. The plant community concept, can be quite helpful in some circumstances, like describing forest succession. But savannas were extremely diverse and heterogeneous. Groves of trees, copses of shrubs, wildflower patches, and grassy lawns expanded and contracted, migrated and disappeared unpredictably following inherently complex patterns of Indian burning, hunting, and horticulture, grazing, climate, pollination, and dispersal. So the notion of plant community is limiting for many ecological questions especially regarding savannas. The ecosystem concept is okay, but focusing on the networks of producers, consumers, and predators doesn’t give justice to the dynamism and heterogeneity of the savanna. Landscape is better, because it implies that there is some spatial heterogeneity and patterns at larger scale. But it still doesn’t encapsulate the temporal heterogeneity, or dynamism. Mosaic is a type of landscape, but is explicitly heterogeneous. Although the concept is not explicitly dynamic, most mosaic landscapes shift and change through time, and so dynamism is at least implied. Because the term savanna mosaic is sufficiently general, it leaves room for the inclusion of multiple ecological perspectives such as community, landscape, ecosystem, and biome.
For conventional descriptions of the savanna, see:
Anderson, R.C. 2006. Evolution and origin of the Central Grassland of North America: climate, fire, and mammalian grazers. Journal of the Torrey Botanical Society 133(4): 626-647.
Axelrod, D. I. 1985. Rise of the Grassland Biome, Central North America. The Botanical Review 51(2): 163-201.
Curtis, J.T. The Vegetation of Wisconsin. Wisconsin University Press, 1959.
Gleason, H.A. 1922. The Vegetational History of the Middle West. Annals of the Association of American Geographers 12: 39-85.
Nuzzo, V. A. 1986. Extent and Status of Midwest Oak Savanna: Presettlement and 1985. Natural Areas Journal 6(2): 6-36