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<br />flooding. The canopy is variable in composition, either composed of a mixture of tree <br />species or strongly dominated by a single tree species. <br /> <br />The species composition of floodplain forests varies both geographically and in <br />relation to such features as substrate type or flood cycles. In southem Minnesota, <br />silver maples, black willows, and cottonwoods are common canopy dominants. They <br />occur either in nearly pure stands or in mixed stands. Scattered individuals or patches <br />of river birch, American elm, slippery elm, green ash, and swamp white oak are also <br />common in stands in southern Minnesota. <br /> <br />The tree canopy cover is highly variable within floodplain forests. The canopy is <br />continuous in some stands while other stands have open areas caused by repeated <br />erosion, ice-scouring, and soil and debris deposition, all of which prevent the growth of <br />trees and shrubs. <br /> <br />In recent decades, Dutch elm disease has also caused significant canopy openings in <br />floodplain forests in which mature American elm trees were abundant in the canopy. <br />Areas beneath tree-canopy openings in the forests are either dominated by short-lived <br />herbaceous plants or, where erosion and disturbance from flooding tend to be <br />repeated and severe, remain unvegetated. The common herbaceous plants in these <br />open patches include those mentioned above in the floodplain forest class description. <br /> <br />Woodlands <br />Oak Woodland/Srushland (MLCCS Code 42120 11,115 Total Acres) <br />A total of 98 occurrences of oak woodland/brushland were documented within the city. <br />These were generally low to moderate quality due to encroachment by brush, lack of <br />appropriate levels of grazing, the <br />absence of periodic fires, and <br />other factors. Although some <br />higher quality sites were noted <br />as well. Oak woodlands <br />observed ranged in size from <br />0.5 to 25.9 acres in size. <br /> <br />Oak woodland-brushland occurs <br />on dry to mesic site~ throughout <br /> <br /> <br />I <br />\~. <br />!t~:_~.~; <br />Oak Woodland-brushland in winter, Cottage Grove, MN <br /> <br />City of Elk River, MN - Natural Resouce Inventory <br />Bonestroo Natural Resources, September 2004 <br /> <br />23 <br />