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<br />increase during the spring period whil~ warm season grasses <br />may be adversely affected. An initial increase in weed growth <br />and infestations may occur, but will be strongly influenced <br />by managerial practices (1). <br /> <br />Summer cumulus precipitation augmentation is expected <br />to have no impact on forest vegetation. Widespread, or prolonged <br />winter snowpack augmentation is expected to improve conditions <br />for spruce and fir to replace aspen and pine along the borders <br />of thei~ ranges and on disturbed sites. However, the effects <br />of slope, exposure, disturbance from fire, insects, etc., <br />are more critical and it is not known if a discernible change <br />in forest vegetation will occur (18). <br /> <br />2.4 Effects of Silver Iodide <br /> <br />Although many methods of precipitation management are <br />being attempted throughout the world, the most popular method <br />is seeding with artificial ice nucleating agents, primarily <br />silver iodide. Silver iodide is released from ground generators <br />as a smoke produced by burning a solution ~f silver iodide <br />complexed with either sodium iodide or ammonium iodide in <br />acetone using propane as a fuel. Pyrotechnic devices, usually <br />called flares, are also used from either ground sites or aircraft. <br />The flares contain silver iodate and a fuel similar to solid <br />rocket propellants. When burned, the silver iodate releases <br />oxygen which combines with the fuel to produce a gaseous com- <br />bustion product. After combustion, a silver iodide smoke <br />remains. <br /> <br />An investigation of the effects of silver iodide in terres- <br />trial ecosystems found that: <br /> <br />2-14 <br />