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habitat. It has been found that many of these forests, whether on an ephemeral or permanent stream, tend to be fairly even-aged. That is, most of the trees in a particular stand are about the same age. This pattern exists because most of these forests are established by intense, scouring floods. Although cottonwood can establish new plants without a scouring flood, scouring floods tend to be the primary source of large groves of cottonwood. Along the major rivers peak flows are often highly controlled now and scouring floods have become much less common. As a result, many of these forests are dying and not being replaced at a rate that would maintain this important vegetation unit in the prairie lands. But on ephemeral streams there is often much less flood control and scouring floods are more common, even though still fairly uncommon. That is, major scouring floods usually only occur every few decades. The forests along these streams are well adapted to that pattern and are generally being maintained. Three negative forces, however, have presented local threats to the future of these forests. One of the most common is grazing. The understory of these forests in the spring provides a rich source of forage for cattle long before the prairie grasses become the primary food source. These forests also provide protection from winter storms and from midday sun in summer. As a result, these forests, when exposed to grazing, are very heavily impacted and often degrade. The ground can become compacted from trampling and the understory composition can change from a rich grassland to a weed infested area. It has been found that simply eliminating the grazing pressure during certain times of the year can maintain these forest environments in good condition. Undoubtedly, the American Bison utilized these areas heavily and thereby the forests adapted to such use. But it is probably also true that cattle utilization does not mimic Bison utilization and therefore, severe impacts can occur. This grazing pressure can also extend into wetland habitats that occur immediately adjacent to or even in the stream channels. This even further impacts the vegetation quality along these ephemeral streams. A second negative force that undoubtedly influences these stream corridors is increased erosion from overgrazing or land development. Such activities elsewhere increases the sediment load into these stream channels, especially during periods of high runoff such as during a prolonged and intense thunderstorm. This sediment accumulates in the channels and often buries the existing vegetation. Sometimes that burial is with clays and other times with sand. But in either case, burial changes the elevation of the channel bottom, and alterations in texture can have very significant negative effects on the native vegetation. Sometimes the vegetation recovers, but often it does not and a stream channel that was originally occupied by rich growths of sedges, bulrushes, and other wetland species becomes nothing but a sand bed that may be mixed with layers of clay. Coal Creek Wetlands and Wetland Mitigation DA Permit 198811488 August 2003 Page 3 of 23