Platte River Management Joint Study Final Report

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f a 22 Mormon Island to 805% near Elm C:reek. Losses have been greater in some individual segments of the ri.ver.. In a 2-mile segment near Odessa, 87% of the channel area has been converted to woody vegetation. Along the North Platte River, channel losses have not been as extensive as on the Platte River. On the North Platte River, losses range from 55% near Lewellen to 78% near North Platte. . The areal extent of river channel loss is substantial. Within the 80.5 miles of the Big Bend of the Platte River, 26,000 acres of river channel have been converted.to other uses; an additional 5,000 acres of river channel on 28 miles of the North Platte River have been converted to other uses. The average loss is 285 t 0 320 acres per mile of river channel in the Big Bend reach. B. The Grassland Complex The vegetat?ve community referred to as the Grassland Complex historically extended beyond the current high bank of the river channel. The Platte River Whooping.Crane Trust analyzed the probable changes in the areal extent of the grassland complex vegetation based on the present area of cover types and the assumption that cropland and most trees did not exist in pre-settlement times within the river channel. Losses of wet meadows (grasslands in the historic high banks of the river), sandhills prairie, alfalfa and emergent wetlands on Iands within 3.5 miles of the r.iver charinel have been substantial. In the Hig Bend of the Platte River grassland losses have ranged from 56% near Odessa tv about 80% near Grand Island and SheZton. The.average loss of the grassland complex in the Big Bend reach within 3.5 miles of the river channel has been estimated at 72% (Currier et al. 1985). Lbsses of the wet meadow-complex along the North Platte River have been considerably less than on the Platte River, ranging from 25% near Lewellen to 37% near North Platte. An average of 31% of the grassland have been converted to other uses along the North Platte River (Table 8). Much of the remaining native grasslands are of marginal value to endangered species and other migratory birds because they are located in small, disjunct tracts within the Platte and North . Platte River valleys. In the Big Bend region over 80% of the grassland complex (about 20.00 tracts) are less than 50 acres in size (Currier et al. 1985). Sm.a11 tracts of grassland make up 22% of the grassland area in the Big Bend, but their mean size is 9 acres. About 40% of the grassland area in the Big Bend is concentrated in a few relatively large.tracts af 300 acres or more (mean = 546 acres). For many bird species the smallest grassl.arid tracts (0-50 acres) d.o.not provide suita.ble habitat no matter how many are avai`lable. Human disturbance in the form of