Documentation of Existing Conditions in the Central Platte Valley

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SECTIONTWO Environmental Setting The BOR is currently creating a new digital land cover/land use database for the Central Platte Valley study area, using 1:24,000 color IR aerial photography flown August 21, 1998. The study area is somewhat larger than the WELUT database, and extends to Lexington. This study tentatively includes about 39 mapping units, which are generally consistent with but more detailed than the 24 mapping units used in the WELUT database. The vegetation and land cover types used in the WELUT database are described below. 2.2.1 Croplands Based on Currier et al. (1985), croplands occupy about 62 percent of the study area, including corn (45.7 percent), other crop (9.1 percent), and alfalfa (7.5 percent). The highest percentages of corn were found in the eastern part of the study area, between Kearney and Chapman. Other crops include winter wheat, soybeans, sorghum, and fallow fields. The area of alfalfa was highest in Segments 10 and 11. In these segments, alfalfa was grown to supply local dehydration plants where it is formed into pellets and sold for feed. There were about 20 dehydration plants between Kearney and Lexington. Croplands were rarely found inside the floodplain boundary, but riverine lands have been converted to cropland in a few areas through clearing and leveling. A minimum mapping area of 10 acres was used for corn, alfalfa, and other crops. 2.2.2 Grasslands About 17 percent of the study area is in pasture and hayland including grassland (12.8 percent) and "wet meadow" (4.5 percent) (Currier et al. 1985). Grasslands were mostly limited to the highly dissected loess bluffs on the ancient river escarpment 1 to 2 miles from the floodplain. Most of the wet meadows (bottomland grasslands) were found on large islands in the river channel, including Mormon Island (Segments 2 and 3), Shoemaker Island (Segment 4), and Fort Farm Island (Segment 7). Grasslands, including hayed, grazed, and fallow lands, were mapped with a minimum size of 5 acres, and wet meadows were mapped with a minimum size of 10 acres. The principal native grass species of upland native prairie grasslands include the following (names follow Great Plains Flora Association 1986): big bluestem (Andropogon gerardii), little bluestem (Andropogon scoparius), sideoats grama (Bouteloua curtipendula), switchgrass (Panicum virgatum), Indian grass (Sorghastrum nutans), blue grama (Bouteloua gracilis), western wheatgrass (Agropyron smithii), junegrass (Koeleria pyramidata), and needle - and - thread (Stipa comata) (Sidle and Faanes no date). Common forbs include scurfpea (Psoralea spp.), dotted gayfeather (Liatris punctata), false boneset (Kuhnia eupatorioides), Missouri goldenrod (Solidago missouriensis), purple prairie clover (Dalea purpurea), aster (Aster sp.), and scarlet globemallow (Sphaeralcea coccinea). Typical shrubs include eastern pricklypear (Opuntia macrorhiza), lead plant (Amorpha canescens), western snowberry (Symphoricarpos occidentalis), white coralberry (Symphoricarpos albus), smooth sumac (Rhus glabra), and soapweed yucca (Yucca glauca). Nagel et al. (1995) evaluated 279 native prairie sites in the Central Platte Natural Resources District (NRD) within Buffalo and Dawson Counties. Smooth brome (Bromus inermis) and ImcreftwWoodwardapo 2-2 68FOD9728600h1.doc 601999(9:52 AM)/URSGWCFSI2 FedWWSWU/M ,7 Lj