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I I I I I I I I I I I I I I I ^I'lI'iO"'~ U'J.......J . U SEcnONTWO EmRQ~nDlentalSelUng now characterize Platte River hydrology influence and maintain the remaining wet meadow habitat. High flow events produce regional changes in groundwater levels which are favorable to aquatic and semi-aquatic organisms including hydrophytic plants, insects, amphibians, molluscs (e.g., snails and clams). Soil thaw, changes in vegetation, snail abundance and distribution, mollusc reproduction, and abundance of violets symbiotically associated with the regal fritillary butterfly (Speyeria idalia), are examples of events that investigators have reported. The natural timing of high river flow is important because biological processes to which native species have adapted are also related to environmental variables, such as day length and temperature. Historic flow records show that two pulse flow periods occurred in the natural hydrological cycle of the Platte River, the first during FebruarY and March and the second more dominant pulse during May and June (FWS 1997). Reduced frequency and duration of seasonal pulse flows shift the wet meadow communities toward more xeric conditions. Reduced frequency of soil saturation also encourages land leveling and conversion of wet meadows to other uses. Bottomland grasslands are important in the use of the Platte River Valley as a staging area for sandhill cranes. Invertebrates and herpetofauna of bottomland grasslands and wetlands constitute an important component of sandhill crane diet during the spring stopover (Currier et aI. 1985. Whooping cranes also feed in wet meadows during migration, and the foraging strategies of whooping cranes are more closely associated with wetland feeding habitats than are those of sandhill cranes in general (Johnsgard 1996). Foods used by migrating whooping cranes, and that are available in bottomland grasslands and wetlands along the Platte River, include small fish, snakes, frogs, frog egg masses, crayfish, grasshoppers, crickets, and other insects (FWS 1981, 1994; Currier et aI. 1985; Ballinger 1980; Cochnar and Jenson 1981; Ratcliffe 1981; Davis and Vohs 1993). Many of these organisms depend on aquatic moisture regllnes, or seasonally moist or saturated soils for all or part of their life cycle. Currier and Henszey (1996) provide a description of Platte River bottomland grassland biology, ecology, and hydrology. 2.8 HABITAT RESTORATION EFFORTS Most of the habitat restoration projects to date have focused on clearing of woody vegetation from islands in order to create an unobstructed river corridor suitable for roosting by sandhill and whooping cranes. Other projects in the Central Platte River Valley have included creation of nesting islands for least terns and piping plovers and restoration of wet meadows. A summary of habitat restoration efforts through 1997 is provided in Table 2-5. As of the end of 1997, approximately 22 miles of river channel have been cleared, five nesting islands have been created, and 1,107 acres of cropland have been turned into bottomland grassland/wet meadow complexes (FWS 1998; Trust 1998). River channel clearing was begun by the Trust in 1982; most of the clearing to date has been conducted by the Trust, on its own or in cooperation with other parties. The Trust uses a Kershaw "Klearway" for river clearing activities. The Klearway has two 400 pound flywheels, each with two-inch blades on a front-mounted, articulated cutting head. The machine is driven through the vegetation and chips trees and shrubs up to eight inches in diameter. A tractor- driven two-way disc follows the Klearway and uproots the remaining vegetation. Clearing BIftiDer Wt1tItIrmrI CIJdI f<<IeQ/ SIll . . 68F00S1728BOQ1r1.doc 6Q!1999(9:S2AM)nJRSGWCFS/2 2-11