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Currently, about 54 percent of the 1.7 million acres of NFS land in the South Platte River
<br />Basin is occupied by sawtimber while only 14 percent is non-stocked or occupied by
<br />seedlings and saplings (Table 2). The reverse appears to be true in the year 1900, for
<br />example, when only 14 percent of the area was occupied by sawtimber and the majority
<br />(62 percent) either non-stocked or occupied by seedlings and saplings. Intuitively, one
<br />would expect a larger sawtimber component in 1900 than was estimated using the
<br />procedure in this analysis to characterize historic stand condition. One factor that limits
<br />the area calculated to be sawtimber is a consequence of the fact the difference in age
<br />between poles and sawtimber is so short on the PSI National Forest that the 20-year
<br />increment exceeds the duration of that size class on the age/basal area relationship and to
<br />some extent, excludes it from selection. Although all stands are grouped into one of three
<br />discrete size classes, the actual basal areas associated with the stands represented in Table
<br />2 have a much more uniform distribution over time and it is the estimate of basal area
<br />that is used in the hydrologic simulations.
<br />Tabie 2. Summary of acreages on NFS land in the South Platte River Basin in the size
<br />classes S(non-stocked forest area and seedlings and saplings less than 4.9 inches
<br />DBH), M(pole stands 4.9 to 9.0 inches DBH), and L(sawtimber stands greater than 9.0
<br />inches DBH) for each 20-year increment from 1860 to the reference year (1997) and
<br />forward to 2060.
<br /> Size Class Acreages
<br />Year S M L Total
<br />1860 824,033 695,586 214,247 1,733,866
<br />1880 672,861 773,564 287,441 1,733,866
<br />1900 1,079,915 566,954 86,998 1,733,866
<br />1920 1,440,700 243,457 49,709 1,733,866
<br />1940 1,111,910 544,704 77,252 1,733,866
<br />1960 737,707 942,554 53,605 1,733,866
<br />1980 138,212 1,422,498 173,156 1,733,866
<br />2000 235,380 563,481 935,005 1,733,866
<br />2020 323,443 57,910 1,352,513 1,733,866
<br />2040 163,021 173,996 1,396,850 1,733,866
<br />2060 14,959 299,437 1,419,470 1,733,866
<br />After the vegetation polygons were characterized, the WRENSS Hydrologic Model was
<br />used to simulate average hydrologic response, by forest type, for the stand conditions
<br />characterized on each polygon for each time interval. Aspect and precipitation for each
<br />polygon was held constant for each time interval, only basal area was altered in the
<br />hydrologic simulation process. For hydrologic simulation purposes, all like polygons
<br />(similar species, basal area (size class), aspect, and precipitation) were lumped to reduce
<br />the number of calculations and shorten simulation run time.
<br />11 2/2/2007
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