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<br />00281 <br /> <br />. <br /> <br />. <br /> <br />Zon emphasized the need to distinguish clearly between total annual <br />discharge of a river 'and the actual behavior of the stream during the <br /> <br />different seasons of the year. It is possible for total annual discharge <br /> <br />to remain unchanged yet for stream regimen to be so changed that utility <br />of the water is greatly reduced. <br /> <br />It has been clearly demonstrated that some changes in forest cover <br /> <br />have caused differences in total evapotranspiration losses. <br /> <br />The experiments that show significant differences in total evapo- <br /> <br />transpiration are those in which natural forest cover was cut in various <br /> <br />degrees. Nearly all the reported experiments are of this type. Only <br /> <br />three tests have been reported where trees were planted on watersheds. <br /> <br />Unfortunately none of these are set up to give particularly precise tests <br /> <br />of the change in total evapotranspiration. <br /> <br />On the watersheds where forest cover has been reduced results have <br /> <br />agreed fairly well with Zon's statement that more water would be consumed <br /> <br />on a wooded watershed. However, his expectation that the effect might <br /> <br />be the greatest in a semiarid region has not been realized. The greatest <br /> <br />changes in total evapotranspiration have, so far, been reported for extremely <br /> <br />wet humid areas. This is not yet definite because there have been few <br /> <br />careful tests in the drier areas. Yet, it appears logical because only <br /> <br />in the wetter regions can vegetation develop to use a maximum amount <br /> <br />of water and only there is there sufficient water to completely prime <br /> <br />watersheds so that the full effect of a change in vegetation can be <br /> <br />realized. The possibility that elimination of trees bordering streams <br /> <br />- 6 - <br /> <br />