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<br />4 <br /> <br />Insect populations, and perhaps ,other pests, are likely to show <br />the greatest effect five to ten years after weather modification starts <br />(depending on the length of life cycle of the organisms and their hosts). <br />Plant biomass will build up first because of increased precipitation, <br />leadin~ to establishment of a new host-insect or host-disease equilibrium. <br />A severe test of the stability of this equi~ibrium will come at times <br />of drought (inevitable even with weather modification) following 5 to 10 <br />years of increased precipi tat ion . <br /> <br />!; <br /> <br />Increases in weed abundance will probably be roughly proportional <br />to the change in mean precipitation. Explosive multiplication of noxious <br />weeds is unlikely as a consequence of weather modification. There may <br />be exceptions to this statement, just as with insects or plant diseases, <br />but the exceptions will be essentially unpredictable (62). <br /> <br />Large mammals, at least in North America, are unlikely to become <br />exti~ct either. totally or within a moderately large region as a consequence <br />-of .weather modification. The number of large and small mammals could be <br />red~ced in some areas by loss of food or habitat or by increase. of winter <br />snow, but land management agencies would be able to provide habitat mani- <br />pulation procedures adequate to maintain at least some members of the <br />species even under ~ltered weather. Such assurance cannot necessarily <br />be given if weather modification is unwisely combined with other environ- <br />mental changes, however(120). <br /> <br />Big game,populations could be adversely affected if artificial <br />increase of snowpack further reduces winter range, whicll is already <br />critically short in many localities. Most contemplated snow pac~ modi- <br />. ficationprograms will conc;:entrate on the zones of deep snow abandoned <br />by large animals during winter, but adequate control may not be attain- <br />able. In any case, there are grounds for b.elieving that the first major <br />ecological effect of weather modification likely to be detected, at least <br />by the general public, is a change in wildlife population structure in <br />certain critical localities. It is perhaps even more likely that <br />weather modification will be widely blamed for real or imagined fluct- <br />uations in wildlife numbers, whatever their cause (34). <br /> <br />EcoZogicaZ Change in Relation to Land Management <br /> <br />Moderately disturbed plant and animal communities will be more <br />sensitive to weather modification than either essentially undisturbed <br />stable communities or continuously disrupted areas such as cultivated <br />fields and home gardens (115). Specifically, if precipitation is arti- <br />ficially increased over range lands, the effect on vegetation compo- <br />sition will be great~r on lightly to moderately grazed range than on <br />range that is either heavily grazed or not grazed at all (25). <br /> <br />.! <br /> <br />Precipitation increaSe .will change the species composition of <br />grasslands primarily through increase in abundance of species formerly <br />confined to wetter sites (23). A moderate increase in precipitation <br />may bring about some decrease in populations of small mammals such as <br />