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<br />,tf;;" <br />~.f) <br /> <br />f' <br />;~..;: ~: <br /> <br />environments, and is closely related to flood-related disturbances. Stevens and Ayers (1993) <br />concluded that wetland vegetation sites floored with silty soils change rapidly from an annual <br />Gnapha/ium chilenselAs/er subula/us association in the first year, to clonal TyphalPhragmi/es <br />association in silt-rich., high-inundation sites, or to woody TamllrixlSalix association in sandy, <br />low-inundation sites. The direction of the successional processes following a flooding event will <br />thus be highly dependent on scour and depositional patterns, and local velocities during the <br />flooding. <br /> <br />" <br />I <br />I <br /> <br />HYJ)Oth~ <br />The planned flood flow from Glen Canyon Dam is expected to alter the existing dynamic <br />condition of wetland and riparian vegetation downstream Colorado River fluvial ecosystem. The <br />following hypotheses will be tested by this experiment <br /> <br />" <br />,. <br /> <br />Null hypothesis 1- <br />HO 1: A planned flood flow from Glen Canyon Dam will not alter the existing dynamic <br />relationships between riverine geomorphology and wetland and riparian vegetation downstream <br />Colorado River fluvial ecosystem. <br /> <br />" <br />/1 <br /> <br />~ <br />~~ <br />"; <br /> <br />, <br /> <br />Secondary-Null Irypotheses- <br /> <br />". <br /> <br />.' <br /> <br />HO la: System-wide reach geomorphology will not influence wetland and riparian <br />vegetation area, patch distribution, structure, composition, or standing crop. <br /> <br />;:1 <br /> <br />" <br />.< <br />.:. <br /> <br />HO Ib: Geomorphologic attributes of specific sites will not interact influence wetland <br />and riparian vegetation area, patch distribution, structure, composition, or standing crop. <br /> <br />;.; <br /> <br />., <br /> <br />AI/emotive Irypothesis- <br />HI: Wetland and riparian vegetation will be significantly altered by the flood flOW; <br />however, recovery of wetland vegetation will proceed rapidly as a function of extent of scour, <br />inundation frequency, grain size, microsite slope, and propagule availability. <br /> <br />'/ <br />. <br />;.~ <br /> <br />Nulllrypo/hesis 2- <br />H02: A planned flood in early spring will not result in significant increases in non- <br />native plant populations in the Colorado River riparian corridor. <br /> <br />" <br />j <br />~!. <br />" <br />< <br />i <br />; <br />~ <br />j <br />~ <br /> <br />, <br />.,,. <br /> <br />AI/emotive hypothesis- <br />H2: The timing of the flooding event will encourage the establishment of non-native <br />wetland and riparian plant species along the Colorado River corridor. <br /> <br />f <br /> <br />Methods <br />This experimental program will investigate three components of flooding effects on <br />riparian/wetland vegetation: (1) before and after surveys of system-wide effects; (2) observation <br />and measurement of flood-related scour of riparian vegetation at sand-bar sites; and (3) model <br /> <br />15 <br />