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<br />--I1AR~~2 FRI -15:05 <br /> <br />.......... ~.. .,.. -~.. <br /> <br />F,04 <br /> <br />I)" 138 <br /> <br />e~pecially in t~e latt~r parts of the growing season, on undivcrted reaches, it <br />13 presuned that the increase in evaporatIve cooling (transpiration) Is <br />re3ponsiole far the Increase~ te~p~rature differences. <br /> <br />Vapor pre3.Sur'e difference is an indIcator of the moisture stress that a plant <br />is experiencing. Plants at low-flow sites developed lower vapor pressure <br />differences, Le.. higher Doisture stress, in llIid- to late 5UJ:lller, while no <br />such respon:ie was evident on und!verted reaches (Smith et al. 1991). Juvenile <br />plants are likely more prone to mortality at 10.... levels of water potent.lal. <br /> <br />Environmental isotope analysis of deuterium concentrations led Srn.ith et a1. <br />(1991) to suggest that these three woody species utilized solI water in sp~ing, <br />surface wate~ In sut;1me~ afte~ the soils dried out a:1d while streanflow was <br />still high, and groundwater in fall aftel"' surface flows subsided and so11 <br />colsture was virtually absent. <br /> <br />The effect of all these changes is that plants on diverted sites are more apt <br />to be pt;.:5hed to the limit.s of their wat~r stre.ss tolerance. Immaturt;l life <br />stages are likely to not survi....e under these artificial extreme conditions <br />(F~nner et 31. 1985). The probable net result wIll be ch~nges i~ the riparian <br />community In terms of extent. and/or structure. Smith et a1. (1991) con~lude <br />"that t.he integrity of riparian communities Is in jeopardy as a result of <br />strear.: diversion." <br /> <br />The effect.s of strea!'Jflow diversion on cottonwood grow~h rates in Bishop Creck <br />have als~ been studied. Regression equations predicting diameter growth of two <br />cottonwood species wel"e developed from en'viroomental attributes. The models <br />expla:ned 74J or more of the annual var-lance in dianeter growth rates, with <br />growing seaSt)n flow lJolur.1e, previous year's ring width, and average m3.xir:!.u:'iI <br />growing S€'as.;m ter.pe['awre -- in order of sigr.ificance (Stromberg and Patten <br />1990 ar.d 1991), Oth€l" grcwth paraneters are flow rel3~~j, such as the vigor or <br />health of the cfincpy, <br /> <br />Haintenance streulRfL:... is the qt.:ar;tity of wa~er :"eqJired tc l:1a~ntain the <br />exist1.1g cO"lf':a.mity. A ~:'l,;rji C:'l '1c:'lrby RlI.5h Cl'~,:;i< suggests that a large <br />p.;rcen':..'\ge of lh.; ~,:l~~lJral f:,1\o is :-':::j,:lirej fol"' nainten;l.:1ce of cotton~ood <br />pcpu:';,.l!.O=-" (Stl'.:rt:<:!!.~ vJ "l,:\~;.~r ~;.90)" .he ~tl..ay at. Blsh:Jp Creel,: concl'Jded. <br />