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Table 3: Estimated Area (Acres) in the Four Major Size Classes for the
<br />Period 1860 to 2000.
<br />Year
<br />Size Class (Acres)
<br />Total Forest
<br />Acres
<br />Non - Stocked
<br />Seedlings/
<br />Saplings
<br />Poles
<br />Sawtimber
<br />1860
<br />397,930
<br />378,594
<br />297,357
<br />33,712
<br />1,107,593
<br />1880
<br />55,385
<br />697,522
<br />92,137
<br />262,548
<br />1,107,593
<br />1900
<br />285,731
<br />654,913
<br />156,462
<br />10,488
<br />1,107,593
<br />1920
<br />35,860
<br />833,308
<br />238,424
<br />-
<br />1,107,593
<br />1940
<br />-
<br />365,292
<br />709,189
<br />33,111
<br />1,107,593
<br />1960
<br />33,057
<br />193,146
<br />789,152
<br />92,238
<br />1,107,593
<br />1980
<br />133,461
<br />132
<br />952,339
<br />21,661
<br />1,107,593
<br />2000
<br />15,567
<br />133,593
<br />339,430
<br />1 619,002
<br />1 1,107,593
<br />The water balance for current stand conditions was then simulated using
<br />WRENSS (Troendle and Leaf, 1980) modified to account for reductions in
<br />interception loss rather than redistribution, for stands reduced in density.
<br />Based on the research, referenced earlier an adjusted set of snow -pack
<br />modifier coefficients were used for lodgepole pine (figure 13), spruce -fir
<br />(figure 14), and aspen (figure 15). The function for aspen was derived from
<br />Rocky Mountain Research Station file data collected in numerous clear cuts
<br />and surrounding forest on Stoner Mesa in southern Colorado and from
<br />thinned aspen stands on the Fraser Experimental Forest. No adjustment in
<br />interception savings is made for aspect in aspen stands. The winter
<br />interception function for lodgepole pine and spruce -fir is that published by
<br />Troendle (1987) adjusted for aspect differences. The aspect adjustment
<br />represents a composite based on more recent research by Troendle, Schmidt,
<br />and others (Troendle 1987; Schmidt and Troendle 1989; Troendle et al.
<br />1993; Troendle and Reuss 1997; Wheeler 1984; Meiman 1987). The winter
<br />precipitation was adjusted by the modifier coefficient appropriate to the
<br />residual basal area in the polygon, as a percentage of basal area maximum
<br />for the specie (100 percent on the x axis equals the basal area at complete
<br />hydrologic utilization). Basal area maximum for spruce -fir is 150 ft2acre'
<br />while it is 120 ft2acre -' for lodgepole pine, and 110 ft2acre' for douglas fir,
<br />ponderosa pine, aspen, and limber pine. The historical water yield,
<br />simulated using WRENSS, along with the estimated area of each size class
<br />is presented in table 4 for each 20 -year increment from 1860 to 2000. A bar
<br />graph (figure 16) presenting area, in acres, in each size class (Y1) and water
<br />yield (Y2) are plotted over year (x) for the 140 -year period from 1860 to
<br />present. The bar graph demonstrates the general shift from a high degree of
<br />less developed stands in 1860 and the gradual progression to presumably
<br />denser sawtimber stands by the year 2000. The simulated reduction in
<br />30
<br />t
<br />F1
<br />1
<br />J
<br />1
<br />P
<br />1
<br />
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