EIS Arapahoe & Roosevelt National Forest, Pawnee National Grassland

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medium to large west, and spruce-fir very large. These were the only regimes ? which would be affected by timber haxveat in the first five decades. Only the effects of clearcutting were estimated using the WRSNSS procedure. \ The effects of partial cutting were estimated by proportioning the water yield from clearcutting by the percent of basal area (SA) removed by the partial cut (e.g. a partial cut removing 30k of the basal area will produce 30k of the water yield of a clear cut), ae suggested by Chuck Troendle. The original WRENSS procedure indicated that the relationship between basal area removed and water yield was not 1:1 (e.g. a partial cut removing 30V of the basal area would be expected to produce less than 30t of the water yield of a clear cut). This has not been borne out by more recent research. The FORPLAN model for the Arapaho-Roosevelt produced a harvest category called "special cuts". This was primarily harvest that would be done to benefit other functions, although it would be accomplished through commercial timber haxvest. After consultation with the forest silviculturist and wildlife biologist about the kind of treatments which could be expected, lodgepole pine special cuts were treated as clearcuts, spruce-fir special cuts as first step shelterwood treatments, and ponderosa pine special cuts as if they would produce no water yield increase because of the lightness of the treatment. Water yield was only be modeled for the first five decades. Regulations require that the FORPLAN model be run for an entire rotation, but that is primarily to ensure that ASQ is sustainable. Five decades is long enough to show trends in changes in water yield from proposed management, and it is also the time period used for analysis of most other resources. ? Two of the input parameters required by the WRENSS model are pre-treatment and post-treatment basal areas. Post-treatment basal area was always zero because we were simulating the effects of clear cuts (see a.bove). We had initially intended to estimate pre-treatment basal area by simply averaging the basal area of the suitable-scheduled stands. Rudy King (RMS biometrician) pointed out that the relationship of water yield to change in basal area was not linear, and that averaging the basal areas to produce an average water yield was incorrect. He suggested that predicting water yield for a number of classes of basal areas for each species and averaging the results would be more robust. However, after examining the results of the FVS modeling and experimenting with WRENSS, it appears that change in water yield is insensitive to the limited range of pre-treatment basal areas predicted by FVS for the first five decades. We modeled the water yield produced by simulating clearcutting of the smallest and greatest pre-treatment basal areas predicted by FVS for the five decades of treatment. There was no difference in water yield between the two for any vegetation regime. The following is a block by block discussion of the data required to drive WRENSS. Area - We selected 100 acres. Because the model delivers results in depth, rather than volume, and because we desired unit water yield, area is not particularly important. However, we wanted a unit large enough so that we didn't experience the logical inconsistency of having windward widths or harvest block areas that were bigger than the unit areas (although it doesn't { appear to matter to the model). Harvest of the entire unit was simulated. ?