Cattle In The Cold Desert, Expanded Edition

Notes

264 The Land Answers deserts have always been considered free of wildWres, and catastrophic Wres were thus not viewed as a form of stand renewal in such habitats. It is a principle of plant ecology that the way an existing plant community isrenewed—orinthecaseofwildWres,destroyed—determinesthecharacteristics of the next community that occupies the site. The introduction of cheatgrass to the salt deserts of the Great Basin brought Wre as a stand-renewal process and set oV a complicated series of actions and interactions that no one yet fully understands. Virtuallynooneaskswhycheatgrasssuddenlyspreadintotheupperportion of the salt desert environments. Was a new type of supercompetitive cheatgrassaccidentallyintroducedintoNorthAmerica?Didthecheatgrass already established in the higher-environmental-potential sagebrush zonehybridizeandthroughnaturalselectionevolveanewformadapted to the aridity of the salt deserts? Perhaps the invasion was the result of climaticchangetoosubtletobereadilyapparentinweatherrecords.The reduction of the range sheep industry that formerly wintered on the salt desertrangesmayhavecontributedtothismulti-million-acreinvasion. ThenativeperennialgrassesvaryintheirresponsestowildWres.Before cheatgrass was introduced, such stands burned late in the summer orearlyfall,whenthegrasseshadmaturedanddriedsuYcientlytocarry a Wre. Under those conditions, probably none of the perennial grasses were injured by the wildWres. The Wres served to eliminate woody species and favored the grasses. Cheatgrass matures in early summer, advancingtheWreseasonintotheperiodwhenthenativeperennialgrasses are still growing. Some species are more susceptible to wildWre damage thanothersundertheseconditions.Themostdestructivethingthatcan happentotheperennialgrassesburnedinawildWreistohavetheirherbageheavilygrazedtheWrstseasonafterburning .Domesticandwildherbivores are attracted to the lush herbaceous vegetation that sprouts in burnsbecauseofreducedcompetitionandmoreavailablenitrogen.The nitrogen may result in a higher protein content of the herbage, which alsoattractstheherbivores.Iftheburnedareaisgrazed,thenativeper264 Epilogue Passing of the Old Guard 265 ennialgrassesneverhaveachancetotakeadvantageofthereducedcompetitionandavailablenitrogen .Ifthegrazingoccursafterthethinstand of postburn cheatgrass is mature, animals will selectively graze every green perennial grass. Federal land management agencies have therefore decreed that domestic livestock may not graze areas burned in wildWres for two years after the Wre. This means the rancher has to Wnd alternativeforagefortwoyearsorsellatleastaportionofhisbroodstock. The impact of such conservation-designed policy is directly related to the extent and distribution of the area burned. The 500,000 acres of rangelandthatwentoutofuseaftertheWresnearWinnemucca,Nevada, in 1985 had a signiWcant negative inXuence on the local agricultural economy. Generally, the area aVected is larger than the actual area burned. If 2,000 acres in a 6,000-acre pasture burn, the entire 6,000 acres is oV-limits for grazing for the two-year period. It is seldom economically feasible to temporarily fence oV the burned acreage from the remaining unburned area. This is especially true if essential resources for livestock, such as watering points, are located predominantly in the burned area. The policy of deferring grazing for two years after rangelands are burnedinwildWresisgenerallyveryunpopularwithranchers.Themore knowledgeable ranchers point out that some fragile range sites should be protected from grazing for perhaps Wve years after burning, but sites that are completely dominated by cheatgrass with few or no native perennialgrassesbecomeherbaceouswildWrefuelbombsduringatwo -year exclusion from grazing. This is an excellent example of the relentless application of an ecological principle in direct opposition to common sense. During the Wrst half of the twentieth century, cheatgrass on the Nevadarangelandswasbiologicallysuppressedbyexcessivegrazingandby theincreaseinsagebrushthatoccurredafterthenativeperennialgrasses were reduced. After World War II, a series of interacting events favored cheatgrass over the native perennials. The range sheep industry greatly Epilogue 265 266 The Land Answers declined for a variety of reasons. Federal land management agencies made a concerted eVort to improve the quality of range management. Community allotments were subdivided to single-permit allotments, making one permittee responsible for the range condition of his or her allotment. The number of livestock allowed on each allotment and its seasonofusewereadjustedtobringthenumbersoflivestockgrazedinto closer agreement with the carrying capacity of the ranges. All of these measures were well intentioned and theoretically conceived to help returnthenativeperennialspeciestodominance .Unfortunately,theecological threshold of Nevada rangelands is determined by a combination of the land’s environmental potential and its successional stage. If a givensiteisabovethisthresholdandthegrazingpressureandseasonof useareproperlyregulatedthroughmanagement,successionproceedsto perennialgrassdominance.Belowthethreshold,reducedgrazingpressureresultsinacyclic ,explosiveexpressionofcheatgrass.Oncecheatgrass dominancehasbeenexpressed,thewayisopenforcatastrophicwildWres that remove the sagebrush and accelerate cheatgrass dominance. ThewidespreadseedingofexoticperennialgrassesonNevadarangelandsafterWorldWarIIgreatlyincreasedtheharvestableforagebaseand reduced the grazing pressure on native perennial bunchgrass ranges. Again the ecological threshold came into play. Higher-potential sites that had a remnant stand of perennial grasses responded favorably. Lower-potential sites without a critical mass of perennials regressed to cheatgrass dominance. The complexity of ecological relations in sagebrush /bunchgrass communities is well illustrated in the exotic perennial grass seeding program. The original seeds faced competition from sagebrush. The rangeland plow was developed to destroy old-growth stands of big sagebrush that lacked a perennial grass understory. The technologies that were developed were very successful.3 About one million of the nineteen million acres of sagebrush/bunchgrass potential rangelands were converted to transitory...