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CONCEPTUAL ECOLOGICAL MODELS Integrated Models 1. Habitat Complexes - The Platte River Management Joint Study (PRMJS) initially developed a conceptual model that describes features thought to be efficient and biologically effective as a long-term land conservation and management strategy for the Platte. This model is based on conservation and recovery goals for the target bird species, their interpretation of the available scientific and ecological information on the targeted species for the Platte, principles and concepts of landscape ecology, and selected professional and expert opinion. The model proposes a"block and segment" land conservation concept the Service believes to be the most efficient and effective in achieving conservation objectives. It includes physical and biological characteristics, and the general size, shape, composition, juxtaposition, and distribution and location of conservation lands, together labeled a"habitat complex." A habitat complex consists of wet meadows, channel areas, and buffers. "Channel area" is the portion of the river that conducts flow and is bounded on either side by stable banks or permanent islands with vegetation that obstructs view. At low flows it includes interconnected small channels and exposed sand or gravel bars and non- permanent islands. "Wet meadows" are areas with a generally level or low-lying undulating surface consisting of a mosaic of swales with wetland soils and vegetation and ridges with upland native or restored grasslands. "Buffer" is used to shield wet meadow or channel habitat areas from potential disturbances. Thus, a habitat complex has a land and water component. 2. Non-Complex Habitat - The states and water users have more recently developed an alternative conceptual landscape model for the target bird species called non- complex habitat. This model is also based on a review of the literature for the target bird species and a consideration of data collected by Districts on the central Platte River. The model proposes an alternative to the habitat. Non-complex habitats for the target bird species in the central Platte include palustrine wetlands and sandpits. Palustrine wetlands provide alternative roosting and feeding habitats for Whooping Crane while sandpits provide alternative nesting and brood rearing habitat for terns and plovers Physical Models 1. Sediment/Vegetation Model - The Sed/Veg Model predicts how changes in river flow and sediment transport into the Central Platte River will affect the geometry of the river channel, channel vegetation, and important habitat characteristics for the target species. The model is based empirical data from 37 surveyed river cross-sections including daily river flow and sediment transport into the Central Platte, mechanical sediment inputs within the Central Platte, and mechanical modifications to the channel itsel£ Functional relationships within the model are based on equations for river hydraulics, sediment erosion, deposition and transport, vegetation establishment, growth, burial and scouring, and ice formation and scouring. Model outputs include daily changes in: l. channel geometry at 37 surveyed cross-sections 2. extent and height of vegetation along each transect