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<br />5 <br /> <br />jackrabbits where grassland vegetation is already in generally good <br />condition. On severely overgrazed range. herbivores may hinder vegetation <br />responses .to increased rainfall. Big game populations on rangeland can <br />probably be somewhat increased by weather modification if proper live- <br />stock and wildlife management practices are followed (27). <br /> <br />~ <br /> <br />Tree growth and growth of associated native vegetation may be <br />somewhat stimulated through partial alleviation of summer water deficits. <br />The precise nature of the effect will depend on. when the artificial <br />rain is applied in relation to the progress of the seasons and within <br />the life cycle of individual species (42). <br /> <br />In regions receiving less than 12 inches of annual prec:ipitat:Lon, <br />an increase in rainfall- will probably be accompanied by an increas4~ in <br />sediment yield. Above about 12 inches. upland erosion should decrl~ase <br />with increased precipitation. Channel degradation and accelerated <br />sediment transport is likely from the lower reaches of rivers in S4~mi.- <br />arid areas as a result of weather modification (29). Changes in rain-- <br />fall intensity may occur as a result of cloud se~ding, and may altl~r <br />patterns of infiltration and erosion (29). Leaching and loss. of tn:Lneral <br />nutrients from the soil may be accelerated by precipitation increase, <br />particularly whe~e the normal vegetation has been severely deple.ted in the <br />past (46). '. . . . . <br /> <br />Wetlands will be affected by increased precipitation. The prE~cise <br />nature of the effect and its desirability or undesirability will dE~pend <br />- on the local situation.' Canprehensivestudies of, the hydrologic arId <br />ecological situation should be made in each specific area having slgni- <br />ficant wetland resources before weather modification is undertaken. . <br />This is especially pertinent with respect to coastal areas having salt <br />marshes that might be affected either directly by increased precipitation <br />or by runoff from adjacent larid. Artificial increase of precipitat.ion <br />could help somewhat to alleviate the critical ecological situationfacfng <br />Everglades National Parkin Florida as a result of land drainage and diversion <br />of flood waters away from the Park,. but this will be only of limited and <br />partial assistance. Reliance should not be placed on weather modification <br />to solve the Everglades problem (45). <br /> <br />. <br /> <br />In the face of anticipated future dema~ds for recreational fishing, <br />any enhancement of freshwater fisheries, as a direct obj ective or by- <br />product of weather modification, could be esthetically and economically <br />important. Conversely. any loss of productive waters would not only <br />be serious in its awn right, but would seriously complicate the task of <br />managing our remaining equatic recreational resources. Hydrologic changes <br />resulting from weather modification may improve the physical environment <br />for fish under one set of geologic and climatic conditions, and damage <br />it under another. No easy generalization about benefits or losses are <br />likely to be forthcoming. but it should be possible to predict the <br />consequences'of hydrologic change for individual streams or watersheds, <br />given an adequate data base (74). <br />