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<br />istorical Range of Variabtility in Water Yiele! <br /> <br />In the first analysis of the historical impacts of forest management activities on water <br />yield from the North Platte River Basin, the data for the stand polygons for the respective <br />national forests were aggregated based on similarities in aspect, elevation, species, and so <br />forth. This process reduced the 23,000-polygon database to a manageable number of <br />aggregates (Troendle and Nankervis 2000). For the later analysis of the North Platte <br />River Basin (Troendle et al. 2003), data were assembled on a geographic information <br />system (GIS) platform by Andrew Peavy (GIS analyst, Forest Service Ecosystem <br />Management Unit, Fort Collins, CO). Stand polygon layers provided by each forest were <br />merged into a composite for all NFS land in the North Platte River Basin. The individual <br />stand polygons were then intersected with Oregon State climatic maps for either <br />Colorado or Wyoming to obtain an estimate of the average monthly precipitation for each <br />of the individual forest stand polygons. For this assessment of the South Platte River <br />Basin, each Forest provided similar polygon information for lands within the watershed <br />boundary. Data compilation was done similarly to the earlier analyses. As part of this <br />effort, Steve Johnson (Renewable Resources Staff, R2, Lakewood, CO) served as the <br />liaison with the Pike-San Isabel (PSI), Arapaho-Roosevelt (AR), and the Medicine Bow- <br />Routt (MBR) National Forests to obtain the vegetation descriptions and disturbance data. <br />The result was the development of a GIS database containing stand-level information <br />characterizing specie composition, age class, aspect, elevation, monthly precipitation, and <br />some post-1997 disturbance activity. The relative location of NFS lands within the North <br />and South Platte River Basins is depicted on Figure 2. Less than 1 percent of the NFS <br />land in the South Platte River Basin is on the MBR National Forest while 53 percent is on <br />the PSI National Forest and 47 percent is on the AR National Forest. <br />Platte River Basin Watersheds <br />and <br />National Forests <br />q.io2p 45p BpMdes <br />q ?o ap op wiometa?s USDA <br />Figure 2. Schematic of the North and South Platte River Basins showing the location of <br />NFS land. <br />4 <br />Legend <br />National Forests (Proclaimed) <br />Arapaho-Roosereit <br />Metlicine Bow-Roun <br />Pike-San IsaLel <br />Watershed <br />Onober 7006 ? South Platle <br />- Map produced hyAndy Peavy <br />, <br />" ForastSers ice j I PI'ane <br />F on Callms,CO ---"-"-""2/2/2007 <br />