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Water Supply Reserve Account -Grant Application Form <br />Form Revised May 2007 <br />7. Please provide a brief narrative of any related or relevant previous studies. <br />Little is known about the effects of insect outbreaks on water yield. This lack of information <br />should alarm water users and land managers who share concerns about peak discharge, <br />streamflow amount and water quality. The 1940s spruce beetle outbreak in the White River <br />National Forest provides some local insight about how northern Colorado basins may <br />respond to current beetle outbreaks. The flow from both the White and Yampa Rivers <br />increased during the decades after beetles killed 30 to 80% of the overstory across much of <br />the forested portions of these basins (Love 1955). However, because of extreme year to <br />year variability in snowfall, the influence of canopy mortality on streamflow was uncertain <br />during the first decade after the outbreak (Bethlahmy 1973). The greatest change in <br />streamflow occurred 15 years after the outbreak (25% increase), and flows remained 10% <br />higher than the pre-outbreak record for an additional decade (Love 1955; Bethlahmy 1973). <br />In Montana lodgepole pine forests, the timing of peak runoff was advanced by two weeks <br />after 35% canopy mortality from bark beetles (Potts 1984). Reduced nutrient uptake and <br />increased soil temperature and moisture in beetle gaps created conditions that favored <br />nitrate leaching from Wyoming lodgepole (Parsons et al. 1986) and other conifer forest types <br />(Huber 2005). These studies suggest that the hydrologic responses after beetle outbreak <br />may be comparable to the effects of logging in Rocky Mountain pine forests (Troendle and <br />King 1985; Reuss et al. 1997), yet large uncertainties about local watershed responses and <br />the consequences of post-beetle salvage activities remain. <br />10