DROUGHT CYCLES AND WETLAND VEGETATION DYNAMICS

Droughts, i.e., two or three or more years of below average annual precipitation, occur every 10 years of so in the America section of the prairie pothole region. Because most prairie potholes are small and shallow, they typically go dry during droughts. These periods without standing water are called drawdowns. Most species of animals, e.g., wetland birds and mammals, cease to use these wetlands during drawdowns. Most aquatic invertebrates and submersed plants survive drawdowns in resting stages. While animals and aquatic plants avoid or endure drawdowns, for many wetland plants drawdowns are the only time they can become established because their seeds cannot germinate under water. Consequently, emergent and wet meadow species, which are often eliminated during wet years when water levels became too deep for these species to survive, can only become re-established during drawdowns. There are even annual and biannual species, called mudflat species, that are only found growing in these wetlands during drawdowns. Changes in water levels alter the composition, structure, and production of the vegetation of prairie potholes as the vegetation adjusts to falling and rising water levels.