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? Y <br />l <br />Conifer <br />Dccic'uous Hardoo4dt§ftis:ed 'Hardwood <br />Scrub <br />20 40 60 80 100 <br />% Reduction in Cover <br />Figure 1 adequately reflect the nature and range of expected hydrologic changes in the <br />South Platte River Basin resulting from changes in forest density, regardless of whether <br />the changes reflect (1) an increase in forest density due to in-growth or (2) a reduction in <br />density resulting from timber harvest, fire, or mortality due to insect attack. <br />500 <br />E <br />E 400 <br />d <br />N <br />? <br />N <br />? <br />C 300 <br />3 <br />0 <br />? <br />R 200 <br />d <br />? <br />.. <br />CO) <br />? 100 <br />c <br />c <br />a <br />Figure 1. The relationship between reduction in vegetation cover and increased <br />streamflow for three vegetation types (redrawn from Bosch and Hewlett 1982). <br />jectiVes <br />The purpose of the project being reported was to conduct an analysis in the South Platte <br />River Basin that parallels the May 2003 report on the North Platte River Basin enritled: <br />"Impact of Forest Service Activities on the Stream Flow Regime in the Platte River" <br />(Troendle, Nankervis, and Porth 2003). Like its predecessor, this report addresses the <br />prediction, or modeling, of the historical range in variability of water yield and the <br />consequence of present and future Forest Service management activities and natural <br />disturbance from fire and insects on water yield from the South Platte River Basin. <br />Vegetation data, activity (management) data, and disturbance data were provided by staff <br />on the three national forests in the South Platte River Basin. Data acquisition was <br />coordinated by the Forest Service Rocky Mountain Regional Office (R2). The data are <br />assumed to represent the best characterization of current vegetative conditions on NFS <br />land in the South Platte River Basin. <br />Initially, the reference (1997) water yield was simulated using current or existing forest <br />condition. After reference, or baseline, conditions were defined and the hydrologic <br />response was simulated, other scenarios were superimposed on current stand conditions <br />and responses in water yield were simulated to reflect the following: <br />a) Historical stand conditions and attenclant water yield simulations for 1860 to <br />present: Stand projections for this and the other tasks followed the simplistic <br />, 2 <br /> <br />2/2/2007