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<br />e <br /> <br />e <br /> <br />little change in growth would be expected. Significant <br />alteration in growth would result only if precipitation <br />management were to delay snowmelt into the period of active <br />growth." [2, p. 3-111J <br /> <br />Two Sierra Ecology Project Workshops examined the effects of precipita- <br />tion increases on vegetation. Workshop I, "An Evaluation of Possible <br />Effects of Weather Modification Upon Forest Insect and Diseases in the <br />AAierican River Basin, California," noted the impacts of a spectrum of <br />events or activities upon the forest. These were similar to those <br />considered in the Medicine Bow and San Juan studies, and included <br />fire, grazing, logging, mining, recreation, and other water management <br />activities. Assuming that cloud seeding would occur during years of <br />below- and near-normal snowfall and produce a 10 to 15 percent increase <br />in precipitation, WorkShOp I reached the following conclusions regarding <br />potential impacts on the forest: <br /> <br />"In normal years, cloud seeding will probably result in: <br />(1) soil moisture equal to or greater than that in un augmented <br />years, (2) snowpacks of longer duration, and (3) a total <br />increase in precipitation that is very small compared to the <br />total for the area over any decade. <br /> <br />"Forest ecosystems at upper elevations are already adapted <br />to handle more 'normal I wet winters than would presumably <br />occur during weather modification. Therefore, an increased <br />snowpack during 'dry' years probably will not induce 'abnormal' <br />changes and might even result in an overall net benefit to <br />forest stands. <br /> <br />~.. <br /> <br />"However, special circumstances should also be considerea. <br />Subnormal precipitation years serve to 'weed out' root <br />diseased trees, suppressed trees, and trees marginally <br />adapted to given sites. If the periOdic "thinning" function <br />resulting from. subnormal precipitation years is el iminated, <br />overstocking and insect/disease problems associated with <br />overstocking or with drought might ocur. However, localized <br />sites which are understocked because of shallow, rocky soils <br />may be benefitted by an increase in stock. <br /> <br />"Some major specific effects can be expected to materialize. <br />However, because of the complex nature of the environmental <br />matrix of soils, moisture, vegetation, yearly climate, <br />cycles of climatic change, and pathogens and insects, it is <br />not expected that conclusive data will De developed from a <br />5- to 7-year pilot program. The effects are: <br /> <br />"l. Since trees grow faster with a plentiful water <br />supply, it is expected that less severe attacks and less <br />mortality from pathogens such as dwarf mistletoe and <br />cytospora canker will occur under augmented condition <br />than under drought conditions. <br /> <br />15 <br /> <br />