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<br />In total, 12 tree species are present on the 1,733,866 acres of forested NFS land in the
<br />South Platte watershed (Table 1). Of those 12, 6 species (aspen, bristlecone pine, Douglas
<br />fir, lodgepole pine, ponderosa pine, and spruce-fir) occupy 95 percent of the forested area
<br />and account for at least that proportion of the streamflow from NFS land. Lodgepole pine
<br />is the most dominant specie on the AR National Forest, occupying about 45 percent of
<br />the forested area. Ponderosa pine and spruce-fir occupy 22 and 21 percent of the area,
<br />respectively. In contrast, ponderosa pine is the predominant species on the PSI National
<br />Forest and occupies 33 percent of the forested area. Douglas fir and spruce-fir are the
<br />next two most prevalent species occupying 19 and 14 percent of the area, respectively.
<br />Lack of specie specific evapotranspiration relationships for the 6 less frequent species,
<br />lumped as other species in Table 1, required that they be combined hydrologically with
<br />the dominant species for simulation purposes. It is unlikely that this necessity altered the
<br />outcome of the analysis. Precipitation estimates for each forested polygon were
<br />calculated by intersecting the individual stand polygon with the Oregon State Climatic
<br />map for either Colorado or Wyoming. Although there was some aggregation of similar
<br />polygons for simulation purposes, this was not done until after all polygon attributes,
<br />including seasonal precipitation, were determined and polygons with identical
<br />characteristics could be identified.
<br />Table 1. Aerial extent (in acres) of all tree species on NFS lands in the South Platte
<br />River Basin. The total area of 1,733,866 acres does not include non-forested NFS lands
<br />(alpine, water, meadows, and so forth). Although 12 species are present, only the area
<br />for the 6 dominant species is presented with the balance of species represented as
<br />"other species".
<br />
<br />
<br />Species Arapaho-
<br />Roosevelt NF
<br />(acres) Medicine Bow-
<br />Routt NF
<br />(acres) Pike-San Isabel
<br />NF
<br />(acres)
<br />Total
<br />(acres)
<br />Aspen 12,147 3,421 127,583 143,152
<br />Bristlecone pine 16,322 0 65,582 81,903
<br />Douglas fir 6,379 1,387 175,413 183,178
<br />Lodgepole pine 362,826 3,930 89,550 456,306
<br />Ponderosa pine 179,113 2,702 304,032 485,847
<br />Spruce-fir 168,973 45 130,707 299,725
<br />Other species 63,411 0 20,344 83,755
<br />Total 809,171 11,486 913,209 1,733,866
<br />Similar to the earlier analyses, the first step was to characterize each polygon based on
<br />current forest stand conditions (species, basal area, aspect, and precipitation) and then
<br />project current stand condition backward in time, using 20-year increments, to the year
<br />1860. This step consisted primarily of identifying specie composition and defining the
<br />size class for each polygon. Five size classes were used to describe the forest cover for
<br />earlier studies on the North Platte River Basin. However, because of limited data for the
<br />PSI National Forest, only three size classes were used for this South Platte River Basin
<br />2/2/2007
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