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Platte River Ecosystem Resources and Management, with Emphasis on the Big Bend Reach in Nebraska


Vegetation and Habitats


Grasslands

Sandhill Prairie

The waters of the sandhills region in Nebraska drain into the Platte River system. It is a major source of sediment for some of the ecosystem. This region developed from wind-deposited sand after the close of the last glacial epoch. Topography consists of rolling steep-sided slopes with level to slightly sloping valleys between the sand dunes. Soils are very sandy, well-drained, and vary in texture from loamy fine sand to fine sand.

Principal grasses of the sandhills prairie include sand bluestem, little bluestem, prairie sandreed, switchgrass, sand lovegrass, blue grama, and needle-and-thread. Typical forbs are silky prairie clover, hoary puccoon, annual eriogonum, prairie coneflower, stiff sunflower, prairie sandwort, and little pricklypear. Leadplant, New Jersey tea, wild rose, western snowberry, and soapweed yucca are the principal shrubs of this community.

Mixed Prairie

The mixed prairie community exists on nearly level terrain both north and south of the Platte River. Because of its topography, most of the mixed prairie has been converted to agricultural production. Soils are deep silty loams derived from loess deposits.

Principal native grasses of this prairie community include big bluestem, little bluestem, sideoats grama, switchgrass, Indian grass, blue grama, western wheatgrass, junegrass, and needle-and-thread. Common forbs include scurfpea, silverleaf scurfpea, dotted gayfeather, false boneset, Missouri goldenrod, purple prairie-clover, panicled aster, scarlet globemallow and eastern pricklypear. Typical shrubs include lead plant, western snowberry, white coralberry, smooth sumac, and soapweed yucca. Recent surveys of these grasslands reveal a major loss of tallgrass components and a paucity of legumes (H. Nagel, pers. commun.).

Shortgrass Prairie

The shortgrass prairie community begins in the western region of the Platte River system in Nebraska where average precipitation varies from 13-17 inches per year. Topography consists of a nearly level to gently sloping plain, dissected in numerous areas by the intermittent streams. Soils are well drained and are mainly loams or silt loams. Because of the flat topography and productive soil, much of the shortgrass prairie has been converted to agricultural production. About 73 percent of Deuel County, Nebraska, which lies entirely within this community, has been developed for cropland.

Common grasses of this community include prairie sandreed, western wheatgrass, blue grama, threadleaf sedge, buffalo grass, little bluestem, sand dropseed, green needlegrass, and Indian ricegrass. Forbs include scurfpea, silverleaf scurfpea, dotted gayfeather, Platte lupine, and broom snakeweed. The shrub layer is generally characterized by rabbitbrush, silver sage, and soapweed yucca.

Sandsage Prairie

The sandsage prairie consists primarily of rolling hilly sand dunes stabilized by grasses. The soils are well-drained sands derived from wind-deposited sand sediments.

Principal grasses of this community include sand bluestem, little bluestem, prairie sandreed, needle-and-thread, blue grama, switchgrass, hairy grama, and purple three-awn. Characteristic forbs include stiff sunflower, prairie spiderwort, annual eriogonum, hairy goldaster, dotted gayfeather, scurfpea and eastern pricklypear. Sand sagebrush is the primary shrub species associated with the sandsage prairie.

Forest

Riparian Forest

Development of riparian forest vegetation along the Platte River, and North Platte and South Platte rivers closely parallels the reduction of river flow levels brought on by the construction of water diversion projects in the upstream reaches of the valley (Johnson 1994, McDonald and Sidle 1992, Knopf 1986, Knopf and Scott 1990, Sidle et al. 1989, Currier et al. 1985, Eschner et al. 1983, Crouch 1979, Williams 1978). The Platte River valley is one of the most heavily forested river valleys on the Great Plains (see map in Powell et al. 1994). Currier (1982) reported that most stands of riparian forest in the Platte and lower North Platte rivers in Nebraska appeared to be of uniform age, suggesting that widespread forest development occurred after changes in hydrological conditions. Reductions in river levels have impeded the scouring action of ice and the shifting of stream sediments (USFWS 1981). Johnson (1994) stated: "Woodland expansion began in the South and North Platte rivers around 1900 and spread downstream into the Platte River. By the late 1930s, vegetation had occupied most of the former channel area of the North and South Platte rivers and was expanding into Platte River channels."

Currier (1982) identified nine distinct forest vegetation types between Lake McConaughy and Merrick County. These types vary by species composition, soils, biogeographic distribution, and the mixture of shrub species. The cottonwood/cedar community is quite prevalent throughout the valley. Cottonwood is the predominant overstory plant species, and red cedar and rough-leaved dogwood prevail in the shrub layer. Other prevalent tree species in riparian forests of the Platte River include green ash, American elm, and diamond willow. Russian olive, river-bank grape, wild rose, false indigo, and coyote willow are important shrub species. Kentucky bluegrass, poison ivy, common ragweed, black medic, white sweetclover, false soloman's seal, water sedge, and Canada goldenrod are prevalent ground layer species.

Wooded River Channel Island

Stabilized vegetation on islands that are raised above the river channel is typically dominated by shrubs and trees (Nagel et al. 1980). The islands with mostly dense shrub growth have an open sandy understory with scattered grasses and forbs.

The considerable variation in river channel island vegetation stems primarily from varying degrees of soil moisture and stage of growth. In general, this community is dominated by coyote willow, false indigo, eastern cottonwood, and diamond willow. Red-osier dogwood is locally abundant. Prevalent understory species include common ragweed, fog fruit, prairie cordgrass, narrowleaf aster, Canada goldenrod, cocklebur, and Japanese brome. Downy brome, white sweet clover, and poison ivy are important understory species on islands where red-osier dogwood and false indigo are prevalent overstory plants.

Rocky Mountain Forest

Small outliers of coniferous vegetation resembling that associated with the Pine Ridge region of Nebraska occur along the North Platte River west from Keith and Garden counties. This habitat type occurs on moderately steep north-facing slopes and in adjacent canyons. Soils are generally shallow loams or silts formed from the underlying sandstones.

Principal plant species associated with the ground layer of this community include little bluestem, prairie sandreed, blue grama, plains muhly, needle-and-thread, sand bluestem, western wheatgrass, Canada wildrye, green needlegrass, and Kentucky bluegrass. Forbs include shell-leaf penstemon, broom snakeweed, prairie goldenpea, false boneset, scarlet globemallow, Missouri goldenrod, and fringed sage. Typical shrubs include silver sage, chokecherry, prickly rose, poison ivy, and soapweed yucca. Rocky Mountain juniper is the predominant tree species, but green ash and box elder occur occasionally.

Wetland Habitats

Prairie Wetlands

Wetlands on the Sandhills in Nebraska developed as ground water seepage areas in the valleys of wind-deposited sand dunes. Soils of the region are principally fine sands of various taxonomic series. Sandhills wetlands are slightly to moderately alkaline (McCarraher 1977). Agricultural development is less intense in this region; the principal land use is grazing of the surrounding native grasslands by livestock. Wetlands are still commonplace.

Prairie wetlands occur within the Rainwater Basin region of Adams, Kearney, Phelps, and Gosper counties and in the sandhills region of northern Lincoln and southern Garden counties. Wetlands of the Rainwater Basin are closed resulting in basins ranging in size from 2.5-963 acres. The wetlands formed on irregular loess deposits modified by wind action (Evans and Wolfe 1967). The Rainwater Basin has a flat to gently rolling topography. Soils are quite fertile, but contain a high percentage of clay that makes them susceptible to both drought and flooding. Nearly 90 percent of the wetlands in the Rainwater Basin were drained and converted to cropland. Emergent vegetation of wetlands in the Rainwater Basin is characterized by hybrid cattail, hardstem bulrush, American bulrush, and various smartweeds (Evans and Wolfe 1967). Vegetation of wetlands in the Sandhills is dominated by hardstem bulrush, American bulrush, and common reed. The principal submerged aquatic species include sago pondweed, muskgrass, coontail, and water milfoil. Wetlands in the Sandhills are surrounded by native grassland. Sandhills fens are the most unique wetland types and the focus of conservation efforts in that region (Steinauer 1995).

Wet Meadow

The wet meadow community occurs along river channels and other low, sub-irrigated areas in open grasslands and colonizing forests (Currier 1982). Its topography is essentially flat. Soils are typically poorly drained silty clay to loamy fine sands derived from accumulated organic matter on alluvial sediments. Wet meadows are distributed throughout the central Platte River region and the North Platte River region, but are more common in grasslands on Fort Farm Island, Shoemaker Island, and Mormon Island. The grasslands typically consist of grazed pastures with ribbons of palustrine emergent vegetation in depressions that follow the natural drainage patterns (Currier 1982). Their hydrology is driven by river stage, precipitation, and freezing and thawing (Henszey and Wesche 1993, Hurr 1983, P.J. Currier, unpublished data).

Vegetation is dominated primarily by sedges including American bulrush, spikerush, fescue sedge, wooly sedge, woodland sedge, Mead's sedge, saw-beak sedge, and fox sedge. Reed canary grass is the predominant grass. Principal forbs include fog fruit, fringed loosestrife, and lady's thumb. Wet soils and grazing by livestock generally reduce the shrub layer in this community (Currier 1982).

Along the North Platte River valley, alkaline meadows are a principal natural habitat and migratory bird stopover area in the valley's agricultural environment. However, most of these meadows have been chronically overgrazed (Nebraska Game and Parks Commission1994). Steinauer (1994) suggested a rotational grazing system and other range management techniques to preserve alkaline meadows while still providing opportunities for ranching.

Riverine Wetland

Riverine wetland vegetation occurs primarily in areas of standing water behind dams and in isolated pools of water adjacent to the river channel (Currier 1982, Currier and Goldowitz 1994). Areas of riverine wetland vegetation occur most frequently along the North Platte River and in widely scattered reaches of the Platte River between Lexington and Grand Island. Hardstem bulrush, American bulrush, cattail, spikerush, water sedge, fog fruit, and coyote willow make up the predominant emergent vegetation of this community.

Open River Channel Island

This community is made up of exposed sandy deposits within the river channels. Open River Channel Islands are usually exposed during the summer as river levels decline from increased evapotranspiration, low precipitation, and increased water demands for agricultural production. Higher river levels during spring result in scouring the islands and the removal of short-lived plant species (Currier 1982). Although well distributed throughout the Platte River valley, the bulk of this community occurs in Hall County between Shelton and Chapman, and in Lincoln County between Hershey and North Platte.

Vegetation characteristic of open river channel islands is typically annuals and biennials that can become established quickly following exposure of the riverbed. Dominant plant species of this community include lovegrass, various nutsedges, cocklebur, barnyard grass, and sand dropseed. Purple loosestrife is becoming well-established in the Platte River channel.

Man-made Habitats

Sand and Gravel Pits

Commercial mining of sand and gravel is commonplace in the Platte River system, Nebraska. Mining operations leave deep ponds surrounded by piles of sand and gravel. Pits are connected to the river or closed and fish communities vary accordingly (O'Shea et al. 1990). Centrarchids make up sand pits lacking aquatic vegetation and non-piscivorous centrarchids and small fish dominate sand pits with aquatic vegetation.

The sand and gravel substrate provide nesting sites for endangered least terns and threatened piping plovers. Where natural sandbar habitat has almost disappeared, such as along the central Platte River, most nesting by these birds occurs at the pits. Mining operations typically take place in wet meadows and such habitat continues to decline accordingly. Exhausted sand pits grow back into dense vegetation or become housing developments.

Shelterbelts

Long, narrow, belts of trees and shrubs occur at the periphery of agricultural fields and near farmsteads. Shelterbelt establishment was encouraged by the Prairie States Forestry Project initiated during the 1930s. In 1979, shelterbelts occupied about 20,510 acres (0.3 percent) of the central Platte area.

Cottonwood and red cedar are the predominant tree species planted in shelterbelts. Other frequently encountered tree species include Russian olive, green ash, American elm, slippery elm, red mulberry, box elder, silver maple, hackberry, Chinese elm, and Siberian elm. The ground layer is usually poorly developed, consisting of various grasses including Kentucky bluegrass and timothy.

Cropland

About 55 percent of the land area in central Nebraska was devoted to some form of crops in 1969 (Bose 1977). This percentage has increased greatly as more grasslands and wet meadows have been converted to cropland and sand and gravel pits. The intensity of agricultural land use ranged from 14 percent in Garden County to 84 percent in Hamilton County (Table 1). Because much of the region was originally native grassland, the changes from agriculture have probably affected bird populations and species diversity. Current agricultural practices of fencerow to fencerow farming, summer fallowing, fencerow removal and shelterbelt removal to facilitate expanded use of center-pivot irrigation systems have probably stressed nesting bird communities.

Corn production is the predominant use of much of the land along the central Platte. Large areas of land in Buffalo and Dawson counties, Nebraska, are devoted to alfalfa production. Winter wheat is grown extensively in the western counties of Lincoln, Keith, Garden, and Deuel.

Residential Habitats

Numerous small towns and cities provide a wide range of habitats for wildlife. Prominent among these are deciduous and coniferous ornamental plantings around residences, parks and cemeteries, industrial areas, grain elevators, building ledges, and landfills. Diverse food sources are provided in these settings, which accommodate the existence of numerous bird species. Graber and Graber (1963) stated that residential habitats in Illinois supported higher densities of breeding birds than any other habitat except ecotones.

Dutch elm disease has spread throughout the Platte River valley, and there is an abundance of dead branches and natural cavities, which provide numerous places for cavity-nesting European starlings and house sparrows. The general lack of other hole-nesters including northern flicker, black-capped chickadee, and white-breasted nuthatch in residential habitats is probably due to competitive exclusion by the more aggressive house sparrows and European starlings.


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