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?:. . <br />Summary of Data Set <br />Data provided to us, by the U.S. Forest Service, described approxiinately <br />23,000 polygons, or homog;ene;ous units of area, that; in aggregate represent <br />the total U.S. Forest Servicf; ovvnership in the North Platte River Basin. For <br />each polygon, the manageme;nt class, cover type (including: specie <br />composition, size class, ba:>al area, age, and cover density, when <br />appropriate), aspect, and elevation, were provided. For each polygon, data <br />are also available to estimate mean monthly precipitation. When simulating <br />hydrologic response, the polygons, or unit areas, expressing similar characteristics were aggregateci to reduce the number of computer runs. In <br />anticipation of the alternati.ves that would be simulated, and the questions <br />that might arise, we interrogated the distribution of the polygons with <br />respect to certain characteristirs. We found, for example, little difference <br />exists in the percentage of U.,_3. Forest Service ownership that falls in the <br />saw log size class, by management class. Wilderness areas do not appear to <br />be any more dominated by larger (older) stands than areas designated as <br />Suitable for Harvest. Althoug;h the largest polygons, or unit areas, are as <br />large as 3000 acres, more than 95 percent of the total forested area, <br />regardless of management cla;ss, is characterized by polygons less than 1 <br />square mile, or 640 acres in si:ze with the majority of the units less than 60 <br />acres. Because of the reAatively small size of the units, on-the-g-round <br />management opportunities will be influenced by the dispersal of the units as <br />well as availability of access to them. The alternatives we will propose will <br />not address that problem but e;xperience with Coon Creek tells us that the <br />real r timber hai-vest and therefore water yield augmentation <br />will not be as great as anticip;ated or simu ate . Appendix p the <br />current database, less the annual precipitarion data. <br />HISTORICAL TRENDS 7IN'WATER YIELD <br />As noted earlier, there are c:urri-Intly 1,107,593 acres of forested land, owned <br />by the U.S. Forest Servic;e, in the North Platte River Basin. Species <br />composition is predominantly 1.odgepole pine and spruce fir (table 2). There <br />are significant amounts of ponderosa pine and aspen with lesser amounts of <br />douglas fir and limber pine; (ta.ble 2). Fifty-five percent of all stands are in <br />the sawtimber class with the rnajority of the balance in the pole size class. <br />27