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~ 21 <br />ti ~^ii~rd~~ ~Yd"t~ ~i~ti' a'b~~rer'~f~ ~~"~~ irt•:+Nl~' ~' <br />,,.,: ; <br />t1~MtF- ~ -b~~ nr~ necessarily scrs~tb~tnla~ <br />This zone is rarely, if ever, inundated during the spring higher water <br />period, but species within it depend on the constant soil moisture supply <br />provided by lateral seepage from the river. Species used as indicators of <br />this zone included boxelder (Acer negundo), squawbush (Rhus trilobata, <br />cottonwood (Populus wislizeni), and large individuals of tamarisk or <br />salt-cedar (Tamarix pentandra). <br />~t~aria~ per ~s~grrti~e~ tii~ ~''~°~. <br />This zone is continuous with the vegetation of the canyon slopes. The <br />species of this zone do not depend upon the river for survival, although <br />they exhibit increased vigor near the floodline. Dominant species included <br />Utah juniper (Juniperus utahensis), big sagebrush (Artemisia tridentata), Mormon <br />tea (Ephedra viridis), others. <br />The width of these zones varied between locations. In places, the <br />upland zone extended to the floodline, eliminating any recognizable <br />riparian zone. <br />The Park Service has made an effort to maintain vegetation in <br />natural condition since 1938, limiting cultural disturbance to visitor use. <br />A secondary source of disturbance are occasional cattle which stray in from <br />surrounding ranches. However, the vegetation along the river corridors can <br />not be described as being in pristine condition, i.e., as it appeared prior <br />to European settlement. <br />----,,_ <br />Severer ~"'~`" <br />,#`{ <br />K ..~ <br />~~~ 4 <br />a ?``~amarisk is well established along both <br />