EIS Arapahoe & Roosevelt National Forest, Pawnee National Grassland

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water yield when stand harveat wae eimulated. We entered the greatest basal area predicted for the first five decadee. Area Cut - For IINIMPACTFD, we entered "zero". For IMPACTfiD, we entered 100 acres. Because the intent was to estimate the unit water yield per acre harvested, it was important that the entire stand be harvested. Fsntering a value for AREA C[7T that is smaller than the stand AREA will reduce the predicted water yield proportionately. BA in Cut - For IINIMPACTfiD, we entered the same baeal area as in BA, aee above. For INPACTFD, we entered zero. Entering a value greater than zero allows the user to use the WRSNSS procedure to estimate the effects of partial harvests. As discussed above, we used the method suggested by Troendle to estimate the water yield of partial harvest based on the predicted water yield of clearcuts. Roughness Height - The model is insensitive to this, if Wind Speed is set to zero as suggested. Default value is set to 1, we left it at that. Windward Width - As discussed above, windward width of clearcut units affecta snow deposition and snow scour. Because we manually adjusted precipitation is adjusted as discussed above, windward width was set to zero to turn off the models adjustment of precipitation. Block Area - If, and only if, WINDWARD WIDTH is entered as zero, the program takes the value entered into BLOCK AREA, assumes a rectangular opening and calculates the length of one side. This value is automatically entered into WINDWARD WIDTH. We set this to zero in order to turn off the models adjustments to precipitation. That ends input into the program. The result is a list of water yield increase values. Three values were produced for every timber regime modeled by FVS, one for each aspect (North, South, and East-West). The three values were reduced to one by weighting them by the area occupied by a timber type on each aspect. The result was a mean weighted unit water yield for clearcuts expressed in terms of acre feet per acre harvested. Yields from shelterwood or other partial harvest treatments were calculated by determining the percentage basal area removal for each step in the shelterwood harvest (as compared to the basal area before the first treatment) and multiplying the clearcut unit water yield by the percent basal area removal to reduce the water yield accordingly. Results from FORPLAN provided the average annual acres harvested for each vegetation regime by each treatment type for each decade. Multiplying the unit water yield increase for each vegetation regime and treatment type (eg. clearcut, lst_step shelterwood, 2nd step shelterwood, etc.) by the average annual acres harvested for each regime and treatment produced an average annual water yield increase for each decade. Summing water yield increases for each vegetation regime and treatment produced a total average annual water yield increase for the decade. Increases in water yield produced by vegetation management persist for many years after the initial treatment as trees regenerate and grow. The water yield declines as the trees grow. To account for persistence in water yield increase, we used the linear 80 year recovezy curve suggested by Troendle and