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<br />Q007P <br /> <br />3.3 million <lUes. Less than oOH-third of the area is <br />under National Forest administration. Tht? Bureau <br />of I.and ~Ianagement administers much of the re- <br />mainder. with 1Il1delt~rmined acreagHs in slate. pri- <br />vale. and Indian ownership. Gambel oilk. mosll)' in <br />brush form. growing 2 to 12 feet high in clumps or <br />thickets. is the predominant sp,:cies. Associated <br />shrubs, which sometimes dominate the site. afe <br />chokecherry, serviceberry. snow berry , big sage- <br />brush. mounlainmahngallY. and olhN woody <br />species. Though somelimesclassified as chaparral. <br />and similar in appearance, the mountain brush <br />Iype differs in Ihal most of the speciils are decidu- <br />ous: thus Ihey are active only in lhe summer. The <br />type is common Iv found al 5.000 10 10,000 feet <br />elevation on relatf\'ely warm. dry expusures. Aver- <br />age annual precipitation ranges from 1fi to 24 <br />inches, less than one-half falling as snow. \\'aler <br />yield of 1 to 6 inches can be expl~cted. <br />There has not belm sufficient resflarch in the <br />mountain brush to accurately predict how treat- <br />ment will affect water rieh!. However, results from <br />plOI studies in Utah {Johnston t't al. 1969J suggesl <br />thai response to brush conversiun may be less than <br />in the chaparral. A rough estimate is 1 103 indws of <br />addilion,lI water from type conversion. If shrub <br />regrowth is not controlled, the increase will be <br />short-lived. probably about 3 to 5 years. It is dif- <br />fkult to estimate the amount of muuntain brush <br />that would or could eVlmtually be converted to <br /> <br />grass. in dew of other resource \'alues and social <br />and economic factors that should be considered in <br />resuurce manag(!rnent decisiuns. <br /> <br />Bi~ Sagebrush <br /> <br />Hig sagebrush (fig. 21) is fuund on some 26 <br />million acres in the Colorado River drainage area, <br />mostly on lands adrninisleTf~d by the Bureau of <br />Land ~1anagement. Only a small percentage of the <br />HI million acres in the Upper Rasin, and none in <br />the Lower Uasin are considered as having putential <br />for increasing water yield. Big sa~wbrush thrives <br />over a broad range in elevation and climate. It is <br />found at ele\'ations up to to.ooo feet. and is well <br />adapted to warm, dry growing seasons ilt lower <br />elevations. Precipitation varies from 8 to 20 inches; <br />only the \....ellest sitHs have potential for water yield <br />improvement by vegetation manipulation. \\'aler <br />yield is less than 1 inch 011 most sag('brush lands. <br />However. where precipitation exceeds 14 inches, <br />yield may he Kreater; it can reach 3 to -I inches on <br />the well est sites. The relocation of snow by winter <br />winds and the resulting watN luss by sublimation <br />are important features of this type. <br />The potenlidl for increasing water yield in big <br />sagebrush is poor1~' defined, although type convN- <br />sion on the most favurable sites Illi~ht increa.se <br />yield by 15%, or lip to one-half inch (Sturges 1975), <br /> <br /> <br />e '~.~,- c- <br />. "~'~T--. <br /> <br />';J <br /> <br />.5: <br />~. <br /> <br />>' <br /> <br />~ <br /> <br />~- ..... <br /> <br />. '- <br /> <br />Figure ZO.-Mounlain brush {moslly Gambel oak, U in Ihis pholo} covers some 3.3 million <br />acres 01 mount. in t.nds in lhe Upper Basin. <br /> <br />16 <br />