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30 The Open Land inganddigestingcoarsegrassesareallruminants.Andthatiswherethe problem with big sagebrush arises. The rumen is a modiWed digestion system that provides anaerobic (oxygen-free)sitesforthegrowthofmicroorganisms.Themicroorganisms break down the woody plant material into components that can be digestedbythehostanimal.Thevolatilefattyacidsthataretheendproductsofrumenbacterialfermentationaretheruminant ’smajorsourceof energy. Cattle can consume small amounts of big sagebrush with no problem. If big sagebrush herbage constitutes a relatively large portion of the diet, however, the activity of the rumen microXora is retarded or inhibited.20 The same is true for mule deer and elk, although these nativebiggameanimalscanconsumemoresagebrushthancattle .Theonly nativelargeherbivorethatmakesbigsagebrushalargeportionofitsdiet is the pronghorn. The inhibition of rumen microXora has been linked to the essential oils in the sagebrush herbage. These volatile oils are composed of terpenecompoundsandtheirderivatives .21 Theamountofvolatileoilsthat individual big sagebrush plants contain depends on the season, the site where the plant is growing, the environmental stress to which the plant issubjected,andthesubspeciesinvolved.Mountainbigsagebrushgenerallyhasalowercontentofvolatileoilsthanbasinbigsagebrush .There are probably inherent diVerences in the quantity of volatile oils among strains of big sagebrush as well, which raises the possibility that plant breederscouldproduceabigsagebrushthatdoesnotinhibitthemicroXora of cattle and mule deer.22 The volatile oils found in big sagebrush mayaVectbrowsersevenbeforetheplantiseaten.Manylargeherbivores apparentlybasetheirforageselectiononsmell.Apparently,thestrongsmelling essential oils in the herbage inhibit browsing.23 Once big sagebrush plants become established, they occupy a site for a very long period. There is a poor correlation between the size of sagebrushplantsandtheirage .Bigsagebrushplantswithmorethantwohundred annual growth rings have been reported. The huge, treelike big Gray Ocean of Sagebrush 31 sagebrush plants that are occasionally found along drainage ways growing on old meadow soils are seldom more than seventy or eighty years old. Their age probably reXects the time when the overgrazed meadows were desiccated by deepening channels, and brush species invaded.24 Not all of the sagebrush found in sagebrush/grasslands is big sagebrush . In the western United States, there are about 422,200 square miles of sagebrush. Of this area, approximately 226,370 square miles is big sagebrush. The next most important species is silver sagebrush, 53,200squaremiles;followedbyblacksagebrush,43,300squaremiles; and low sagebrush, 39,100 square miles. In the Humboldt Basin of northern Nevada, 45 percent of the landscape is dominated by species ofsagebrush:40percentisbigsagebrushand5percentislowsagebrush. Sagebrush species may be successional dominants in pinyon/juniper, mountain brush, and mountain conifer communities in addition to the 45percentofthelandscapethatistruesagebrush/grasslands.InnortheasternCalifornia ,thesagebrush/grasslandsareroughly50percentlow sagebrush and 50 percent big sagebrush.25 Silver sagebrush is often associated in the Intermountain area with the Wne-textured soils and seasonal Xooding of old lake basins. Silver sageisrestrictedtotheeastsideoftheSierraNevadaandeasternOregon and does not extend down into the highly saline/alkaline soils in the depths of the Intermountain deserts. Silver sagebrush does sprout after the aerial portion of the shrub is removed; however, because of the nature of the habitat it occupies, it is seldom burned in wildWres. The various subspecies of silver sagebrush are widely represented in the northern Rocky Mountains and the major river valleys on the eastern slope of the Rocky Mountains. Black sagebrush and low sagebrush are the major components of the groupofsagebrushspeciesaptlynamed“lowsagebrush.”Thesespecies areusuallyone-thirdtheheightofbigsagebrush.Althoughsimilartobig sagebrush in appearance, they often occupy very diVerent landforms. Low sagebrush is usually on the oldest landform in a given landscape 32 The Open Land wheresoilshaveawell-developedclayhorizonclosetothesurface.Clay soilstakeupwaterveryslowly,andlowsagebrushXatsareextremelywet andstickyinthespring.Conversely,whendry,thesoilsarebakedbrickhard .26 Lowsagebrushishighlypreferredoverbigsagebrushbybiggameand domesticanimals.Sheeppreferblacksagebrushfortheirwinterbrowse. OnthemarginsoftheCarsonDesertinwesternNevadathereareextensive stands of black sagebrush. After a century of winter use by sheep, thesemonospeciWccommunitieslookliketheyweretendedbyahostof LouisXVgardeners.Eachshrubisperfectlymoldedinaground-hugging exotic shape. Oftenonlytwelvetoeighteenincheshigh,lowsagebrushspreadsover the landscape in a tidy gray Wlm quite unlike the uneven texture of big sagebrush landscapes. Because they are old landforms, low sagebrush Xats often have biscuit-and-swale topography. The biscuits have shallow ,moundedsoilproWles,andtheswalesmaybedevoidofsoilwithonly stringers of frost-sorted rocks present. Plant communities called “balds” occur on high, exposed ridges. These communities are dominated by low sagebrush shrubs scarcely four inches tall that are shaped by winter gales. Throughout the range of the sagebrush/grasslands there are a series ofplantcommunitiesdelineatedbythedominantshrubspeciesandthe understory grass species. To those unfamiliar with them, this network of species may appear to be a bewildering array of variability. In fact, however, the plant communities are repetitive and easily identiWable. Recognizing them is important because they are phytometers, or living measurements,ofagivenlocalecosystemcomposedofsoil,topography, climate, animals, and the plants themselves. The best-known big sagebrush community is big sagebrush/bluebunchwheatgrass ,whichdominatesintheColumbiaBasin,easternOregon , much of Idaho, and extends down the higher elevations into the Great Basin. This is a bunchgrass community in which the dominant Gray Ocean of Sagebrush 33 grass occurs in distinct bunches as opposed to a continuous carpet. In a bunchgrasscommunity,muchofthesoilsurfaceisexposed;only20–30 percent of the area is...


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