Part of the1935 USGS 7.5' quadrangle map of Cahokia area illustrating the absence of significant topographic relief of the American Bottom.
|Topographic relief, however slight, is particularly important in influencing the plants that grow at specific floodplain locations. This is because (a) elevation effects a plant's roots distance to the water table, (b) minor changes in elevation have considerable impact on a location's likelihood of flooding, and (c) the time it takes for it to drain after a flood. Hydrophytic (water-tolerant) plants can survive and even thrive in places subject to frequent flooding. Plants requiring better drained soils are found on the slightly elevated ridges, but even here, periodic flooding will temporarily destroy plant and animal communities and create conditions suitable for occasional invasion of hydrophytic species. Then through time, habitats change as soils drain and conditions improve for plants and animals prefering drier conditions. In this manner, both annual and catastrophic flooding maintain habitat diversity and biological productivity in the American Bottom.|
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