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responses. Potentially, the most significant hydrologic impact after fire is the increased <br />stornl response and elevated sediment production that can and did occur immediately <br />after the fire. Hydrophobic soils that develop as a result of fire limit infiltration of <br />rainfall, and sometimes snowmelt, into the soi] causing a greater amount of surface or <br />overland flow to occur. Surface flows carry more sediment and cause rapid responses in <br />streamflow. The hydrophobic soil condition often dissipates within a few years after even <br />the severest of fires and the capability of the soil to infiltrate precipitation quickly returns <br />to pre-fire conditions. Vegetation gradually reoccupies the site, and the burned area <br />begins hydrologic recovery. By 2020, 18 years after the burn, the area likely will be well <br />vegetated with grasses, forbs, shrubs, and trees. The severity and extent of the Hayman <br />Fire may retard reoccupation by woody vegetation, but woody vegetation will eventually <br />reoccupy the site. The burned area will likely recover hydrologically in 80 or 90 years. <br />Delays in seeding and regeneration could extend the recovery period while rapid re- <br />growth could shorten the recovery period. The limited age/basal area data for the PSI <br />National Forest and the species of interest suggest that on average it is a reasonable <br />assumption that hydrologic recovery will occur in 80 or 90 years after the fire. Since the <br />decline in water yield appears to occur most rapidly towards the end of the recovery <br />period, the simulated increases in water yield in estimated to occur in 2060, 58 years after <br />the fire, seem reasonable. In a study of the impacts of the 1988 Yellowstone fire on water <br />yield, Troendle and Bevenger (1996) found that water yield on the burned watershed <br />appeared to increase in proportion to the percentage of tree mortality and in similar <br />proportion to that observed elsewhere after timber harvest or insect mortality. Peak flows <br />after snowmelt did not appear to be increased; they may have decreased. The relative <br />magnitude of the increases in water yield observed after the Yellowstone fire are similar, <br />when adjusted for precipitation differences, to those simulated to occur after the Hayman <br />Fire. <br />The 108,112 acres of forest vegetation consumed by the Hayman Fire represents about 6 <br />percent of the 1,733,866 acres of NFS land in the South Platte River Basin. The increases <br />in water yield that are simulated to occur on site (Table 4) represent increases in water <br />yield of 0.21, 0.16, and 0.11 area inches from all NFS land in 2020, 2040, and 2060, <br />respectively. These increases would not be detectable at any existing stream gauge in the <br />basin, and the increases would not overshadow the 44,000 acre-foot decline (Table 3) in <br />water yield that will occur as the burned area recovers and the balance of the vegetation <br />on NFS land matures. <br />21 2/2/2007