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Bulletin American Meteorological Society run, avalanches occur under rare conditions of recog- nizably high avalanche danger, when cloud seeding would be suspended under accepted procedures. In areas of high avalanche frequency, such as many chutes in the Red Mountain Pass area of the San Juan Moun- tains, many avalanches run during nearly every major storm, and successful forecast and warning procedures have been developed, at least partially under the spur of prospective precipitation management. The occur- rence of delayed avalanches, after the storm has passed, is related partly to the augmented part of the snow load and mostly to features of snow stratigraphy and meta- morphosis not affected by precipitation management. To the extent that precipitation management focuses at- tention on avalanche warnings and countermeasures, it will tend to reduce, not increase, the hazard. 3) GEOMORPHIC PROCESSES In its effect on geomorphic processes of soil erosion, mudflow activity, and transport of dissolved solutes, snowpack works through processes at a secondary level, through indirect links with vegetation and small mam- mals. Soil erosion occurs mostly in summer and where vegetative protection is lacking, and it tends to be greater at the margins of late-lying snowbanks where vegetation is sparse. Thus, an increase in the extent of late-lying snowbanks would likely have a discernible but highly localized effect on soil erosion. In the San Juan Mountains it was concluded that "other forms of man-induced erosion usually overwhelm the natural variability since they involve increases of orders of magnitude rather than a few tens of percent" (Caine, 1976). 4) STREAM RUNOFF Snowpack augmentation affects stream runoff and reo lated characteristics mostly in the headwaters portion of watercourses where regulation is usually absent. Simu. lation of particular sites under study has shown that precipitation management there would have no identi- fiable effect on the frequency and magnitude of flood flows. 5) ALPINE VEGETATION The impact of snowpack augmentation on alpine vege- tation has been investigated mostly by installing snow fences to increase local snow accumulation in a gross manner and then observing the subsequent vegetational changes. In the San Juan Mountains, Webber et al. (1976) found that a I-week delay in snowmelt would occasion only a small reduction in biomass productivity, becoming serious for a 4- to 5-week delay. They con- cluded that a 15-30% snowpack increase over several decades would cause both qualitative and quantitative changes in vegetation, minor in nature and affecting probably <10% of the alpine area, and that the inci- dence of rare species might increase as a result. "These conclusions," they said, "refute the popular notion that tundra is a fragile ecosystem." On the San Juan Ecology Project, several study plots were located in subalpine forests and adjacent grassy 495 parks. The distribution of tree species was found to be strongly related to snowmelt date, which, in turn, de- pended greatly on elevation and exposure, southern slopes in the forest zone often becoming snowfree be- tweeen storms during the winter. Spruce growth was independent of snowpack depth, the amount of growth being apparently genetically controlled, whereas aspen was more responsive to spring soil temperature. Seasonal growth of ponderosa pine was positively correlated with the precipitation of the previous December. Stable aspen stands give way to fir, then spruce, as one goes to sites with longer snow duration and lower temperatures (Dix and Richardson, 1976). The seedling stage is the most sensitive to increased snow duration, and the maximum density of seedlings would tend to shift to sites that now have earlier snowfree dates. Variations in wood production directly attributable to delay of snowfree date were not detected. In spruce and fir, wood production was found to be constant. Among the herbaceous plants, the timing of the earliest phases of seasonal development was found to vary directly with the snowfree date, but this depen- dency became less and less marked as the season pro- gressed, and all species completed their development within the growing season. Although precipitation man- agement might delay the phenological coming of spring, especially in pockets of snow accumulation, it was con- sidered unlikely to have a direct effect on herbaceous populations except perhaps to reduce biomass produc- tion somewhat. In oak brush, which in parts of the San Juan Moun- tains is an important browse for elk, production was found most closely related to the amount of the previous summer's precipitation and to be very little affected by snowpack. In the Medicine Bow Mountains, decomposition of litter was found to be unaffected by increased snowpack. Leaching of nutrients from the soil did not appear to be large, but adequate determination of it was not achieved because of premature termination of the study due to funding cuts (Knight, 1975). 6) ANIMAL POPULATIONS The relationship between snowpack augmentation and the winter range of elk was studied in the San Juan Mountains (Sweeney and Steinhoff, 1976). About 28% of the relevant elk winter range, as mapped by the Colorado Division of Wildlife, fell within the study area of the Skywater cloud seeding experiment, all of that range being within the portion of the study area desig- nated as upwind flank. It was found that a hoof penetrable snow depth of 40 cm initiated downslope migration, whereas a penetrable depth of 70 cm or more was avoided. In a model of winter range in the Mission- ary Ridge area, a 15% snowpack increase was found to correspond to a decrease in this part of the winter range varying from 0 to 20% depending largely upon ante- cedent snow conditions. Springtime upslope movement was regulated by the greening of vegetation rather than by retreat of snow line, and in each season there ap- peared to be ample habitat available for calving. The