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J. Range Manage.57:161-168 March 2004

Can spring cattle grazing among young bitterbrushstimulate shrub growth?DAVE GANSKOPP, TONY SVEJCAR, FRED TAYLOR, AND JERRY FARSTVEDT

Authors are Range Scientists, USDA-ARS, Eastern Ore. Agr. Res. Ctr., 67826-A Hwy. 205, Burns, Ore. 97720; Wildlife Biologist, USDI-BLM, 28910 Hwy.20 W., Hines, Ore. 97738; Habitat Biologist (retired), Oregon Dept. Fish and Wildlife, Box 8, Hines, Ore. 97738.

Abstract

Due to its palatability nd forage quality, antelope bitterbrush(Purshia ridentata ursh DC) is a desirable hrub across westernUS rangelands. Because ittle information s available regardinggrazing management of young bitterbrush, a study was under-taken to explore stocking pressure thresholds and quantifyeffects of light and heavy spring cattle grazing on shrub growth.Rates of browsing and trampling and forage availability were

monitored over 3 years in southeast Oregon. Across years, 29%of bitterbrush endured trampling in light-grazing treatments,and 55% experienced trampling under heavy grazing. Linearmodels relating ime and cattle density successfully xplained r2= 0.84-0.86) probabilities f bitterbrush being trampled. Forageutilization averaged 32% and 59% in lightly and heavily grazedunits, and 14 and 62% of bitterbrush were browsed n lightly andheavily-grazed pastures, respectively. Cattle began browsingwhen herbaceous standing crop declined to 100-150 kg ha-'.Browsing n heavily-grazed astures reduced diameters of bitter-brush by 4.5 to 9.5 cm in 1998 and 1999, but shrub height wasunaffected. Lightly-grazed stands exhibited a 50% greaterincrease n bitterbrush diameter, 30% greater height ncrement,and 8% longer twigs than shrubs in ungrazed pastures. At theend of the 1997 and 1998 growing easons, bitterbrush n heavily-grazed pastures were 11 cm greater n diameter han ungrazedcontrols and equal to shrubs n lightly-grazed astures. To stimu-late bitterbrush growth, young stands can be lightly-grazed 30to 40% utilization of herbaceous orage) by cattle when bitter-brush s flowering and accompanying rasses are in vegetative olate-boot tages of phenology.

Key Words: Purshia ridentata, ivestock, big game, winter range,wildlife, habitat, browse

Antelope bitterbrush (Purshia tridentata Pursh DC) is animportant shrub for mule deer (Odocoileus hemionus hemionus),pronghorn (Antilocarpa americana), and livestock on western

North America rangelands Kufeld et al. 1973, Vavra and Sneva1978, Neal 1981, Urness 1981, Kinuthia t al. 1992). With a sus-tained crude protein content above 8.0% (Hickman 1975 andKituku et al. 1992), bitterbrush an substantially nhance late-season diet quality of ruminants when nutritive value of herba-ceous forages has declined o sub-maintenance evels (Ganskoppand Bohnert 2001). Bitterbrush ccurs among numerous egeta-

Eastern Oregon Agricultural esearch Center s jointly operated y the OregonAgr. Exp. Sta. of Oregon State Univ. and the USDA-Agricultural ResearchService.

Manuscript ccepted 1 Jul. 03.

Resumen

Debido a su gustocidad y calidad de forraje el Antelope bit-terbrush Purshia ridentata ursh DC) es un arbusto deseableen los pastizales del oeste de U.S.A. Debido a que hay poca infor-macion disponible respecto al manejo del apacentamiento deplantas j6venes de Bitterbrush , e condujo un estudio paraexplorar os umbrales de la presion de apacentamiento cuan-tificar los efectos del apacentamiento igero y fuerte de ganado

en primavera obre el crecimiento del arbusto. Durante 3 aiiosen el sudeste de Oregon e monitorearon as tasas de ramoneo ypisoteo y la disponibilidad e forraje. A traves de los anlos, 9%del Bitterbrush olero el pisoteo en los tratamientos e apacen-tamiento igero y en los tratamientos de apacentamiento uerte55% del Bitterbrush ufrio el pisoteo. Modelos ineales rela-cionando iempo y densidad de ganado explicaron xitosamente(r2 = 0.84-0.86) las probabilidades del Bitterbrush de serpisoteado. La utilizacion del forraje promedio 32% y 59% en lasunidades apacentadas ligera y fuertemente y 14 y 62% del

Bitterbrush ue ramoneado en los potreros apacentados igeray fuertemente respectivamente. El ganado inicio el ramoneocuando a biomasa de las herba&ceas iminuyo a 100-150 kg ha-'.El ramoneo n los potreros con apacentamiento uerte redujo osdiametros del Bitterbrush e 4.5 a 9.5 cm en 1998 y 1999, perola altura del arbusto no fue afectada. Las poblaciones conapacentamiento igero mostraron un incremento del 50% en eldiametro del Bitterbrush , 0% ma's en la altura y las ramasfueron 8% mas largas que las de los arbustos en los potreros inapacentamiento. l final de las estaciones de crecimiento e 1997y 1998 el Bitterbrush e los potreros apacentados uertementefueron 11 cm ma's grandes en diametro que los arbustos de lospotreros control sin apacentamiento igual a los arbustos de lospotreros igeramente pacentados. Para estimular l crecimientodel Bitterbrush as poblaciones jovenes pueden ser ligera-mente apacentadas (30 a 40% de utilizacion del forraje her-baiceo) or el ganado cuando el Bitterbrush sta en floracion ylos zacates acompafiantes stin en las etapas onologicas de crec-imiento vegetativo fines de embuche.

tion types across approximately 140 million hectares (Hormay1943) from British Columbia o California nd east into Montanaand New Mexico (Cronquist t al. 1997).

Senescence, wildfires, a history of excessive herbivory, andlow recruitment ave, however, decreased bitterbrush bundanceacross much of its range Billings 1952, Tueller and Tower 1979,Winward nd Alderfer-Findley 983, Ayers et al. 1999, Clementsand Young 2001), and restoration efforts have frequently metwith limited success (Hubbard 1964, Kituku et al. 1995).

JOURNAL OF RANGE MANAGEMENT 57(2) March 2004 161

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Hubbard 1957) and Dealy (1970) showedthat competing vegetation m substantial-ly reduce establishment and subsequentstature of bitterbrush eedlings, and plantsmust reach an age of 60 to 75 years beforemaximum annual yield is realized(McConnel and Smith 1977). Burning yp-ically results n greater motalit of bitter-brush than does clipping or rotobeating

(Mueggler and Blaisdell 1958, Clark et al.1982), and heavy browsing may alsoreduce plant longevity (McConnel andSmith 1977). While young transplantsappear o benefit from grazing protection(Dealy 1970, Ferguson 1968), establishedbitterbrush generally responds well todefoliation, and grazed plants producemore and longer twigs than ungrazed on-trols (Tueller and Tower 1979, Billbroughand Richards 1993, Kituku et al. 1994).Ganskopp et al. (1999) found that cattleonly browsed bitterbrush ightly beforecompeting grasses entered anthesis, andthat shrubs n pastures ightly-grazed bycattle early in the growing season werelarger n stature han cohorts n ungrazedcontrols. Spring mowing of competingvegetation also stimulates twig growth(Kituku et al. 1994). Accelerated twiggrowth may not occur on less productivesites (Kituku et al. 1994), and in someyears annual production f twigs may alsobe affected by extremely ow temperatures(Jensen and Umess 1979) ador fluctua-tions in annual precipitation (Garrison1953, Kindschy 1982),

Most bitterbrush esearch has focusedon well-established tands or reclamationefforts, and there is little data regardinggrazing management of young stands.Given that light, early season cattle graz-ing stimulated growth of 3 to 5-year-oldbitterbrush Ganskopp t al. 1999), a studywas designed to evaluate bitterbrushresponses o even heavier grazing applica-tions restricted olely to the early growingseason. The objectives of this researchwere: 1) to determine he effects of lightand heavy early season cattle grazing onthe subsequent tature and twig growth of6-9 year old bitterbrush and 2) explorerelationships among indices of forageavailability and levels of browsing onshrubs to determine f stocking pressurethresholds or management f young bit-terbrush stands could be established,These were accomplished by monitoringrates of shrub use, trampling amage, or-age availabil:ity, nd sta re of young bit-terbrush n lightly, heav:ilyf nd ungrazedpastures.

Methods

Study site history and descriptionIn 1990, wildfire charred about 30,000

ha of Bureau of Land Management(BLM), United States Forest Service, anddeeded propety north and west of Bums,Ore. Much of the area consisted of pine-forest/sagebrush-steppe-transition ange

which had historically been graed by cat-tle and was important winter range formule deer and elk (Cervus elaphusnelsoni). Revegetation efforts beganimmediately, and BLM properties wereseeded with 'Secar' Snake River wheat-grass (Elymus lanceolatus (Scribner &J.G. Smith) Gould) at 9 kg ha, and n aeaswhere it had prviously existed, antelopebitterbrush as included at a rate of 2.2 kgha. The bitterbrush seed was acquiredcommercially, ut ts collection ocale wasunknown.

Soil in the ea (43 37'N 119024'W, le-

vation 1,584 m) was a fine, montmoril-lonitic, rigid Typic Argixeroll. Vegetationprior o the fire included a scattered ver-story dominated by western juniper(Juniperus occidentalis Hook.), a shrublayer characterized y mountain big sage-brush (Artemisia tridentata subspp.vaseyana Rydb.) Beetle) with a minor bit-terbrush omponent, nd herbaceous ege-tation dominated y bluebunch wheatgrass(Agropyroi spicatum (Pursh) Scribn. &Smith) and bottlebrush squirreltail(Sitanion ystrix (Nutt.) Smith).

In the absence of competing woody veg-

etation, surviving herbaceous plants andemerging seedlings responded well in thegrowing seasons following the fire.Bureau of Land Management samplingdetected 8,450 bitterbmsh eedlings ha-' n1991 and 3,410 ha' in 1992. Crop-yearprecipitation September-June), which ishighly correlated with annual orage pro-duction in the region (Sneva 1982), was91 and 86% of the long term mean (255mm, n = 40) for the 1991 and 1992 grow-ing seasons, respectively (NOAA 1990-1999, Squaw Butte Station 43029'N119043'W). n accordance with BLM poli-cy, livestock grazing was not allowed in1991 and 1992 to aid recovery of vegeta-tion, and the charred remains of smalltrees and shrubs provided the only evi-dence of the fire fter 2 growing easons.

Pastures and grazing schedulesProject design was a randomized om-

plete block having 3 replications and 3treatments with individual pastures N=9) serving as experimental units.Treatments ncluded pastures hat were: 1)

lightly-grazed y cattle, 2) heavily-grazedby cattle, and 3) ungrazed controls.Treatments were not randomized n suc-ceeding years, so findings reflect cumula-tive effects applied across 3 consecutivegrowing seasons. Also, teatment designa-tions reflect cattle applications nly, eventhough ummering ronghom Antilocarpaamerican) and wintering eer and elk hadfree access to all pastures.

Size of grazed pastures anged rom 0.6to 0.9 ha and ungrazed controls werebetween 1.4 and 1.6 ha. In 1997 grazedpastures were stocked on 5 May with year-ling Hereford x Angus bulls weighingfrom 317 to 363 kg. Lightly-grazed pas-tures supported I animal, heavily-grazedpastures upported , and grazing contin-ued for 20 days. Given our desire to con-fine grazing reatments o the boot stage ofphenology or the grasses and remove cat-tle bfore rapid elongation of bitterbrushtwigs, we doubled he ninti stocking ratesfor the next 2 grazing seasons. In 1998lightly-grazed pastures supported 2 cowsand heavily-grazed pastures supported 4cows with the trial beginning on 21 Mayand lasting for 12 days. Dry Hereford xAngus cows with a mea weight of 453 kg(SE = 26) were used. In 1999, 18 cowswere drawn rom a group of dry animalsscheduled or culling, and mean weight wasslightly heavier (V= 567 kg, SE = 14.5).Pastures were stocked on 4 June and graz-ing continued or 10 days in 1999. Giventhe increase in stock numbers between1997 and 1998, and he use of successivelylarger animals as the trials

progressed,effective stocking rate (AU ha-') progres-sively increased ach yea

Shrub and vegetation amplingEndpoints of 91-m line transects were

marked with metal staes in each pastureand the position along the tape and dis-tance left or fight of the tape recorded for25 randomly-selected itterbrush n eachpasture. Throughout he trials, any bitter-brush ost to complete defoliation or mor-tality was replaced with the nearest avail-able neighbor. Prior to each grazing ses-

sion, the dimensions (greatest diameterand height) of bitterbrush were measuredin all pastures, nd the ends of any recent-ly defoliated wigs maked with black inkto facilitate detection of subsequentbrowsing. To index mass of standing rop,all herbage was clipped from ten, 1-miplots in each pasture ust before stockingoven dried at 40C, and subsequentlyweighed

Durnug razing ri 5 werturned evey2 days, relocated ach bittrush, and abl

162 JOURNAL OF RANGE MANAGEMENT 7(2) March 004



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lied evidence of recent defoliation or tram-pling. Defoliation signs included twigsdisplaying a clipped appearance with newyellow wood on the ends or bark skinnedfrom the last few millimeters f the termi-nal by a cow's biting and pulling motions.Broken stems and twigs or recently dis-placed bark hat revealed bare wood wereconsidered signs of trampling. Stockingwas terminated in all pastures when atleast 50% of the herbaceous forage hadbeen utilized or 80+ % of the sampledshrubs exhibited some sign of utilizationin the heavily-grazed reatment.

After cattle were removed, tanding ropwas sampled by clipping ten, 1-m2 plotsper pasture o estimate forage utilization,and the greatest diameter and height ofeach shrub was recorded to facilitatebefore and after grazing comparisons ofbitterbrush tature. Finally, shrub dimen-sions were measured a third time in lateAugust to assess spring treatment ffectson subsequent summer growth. Again,greatest height and diameter were recordedfor each shrub. n addition, ength of cur-rent season's twig growth was tallied or 2randomly-selected wigs on each plant.

Statistical proceduresA repeated measures analysis of vari-

ance was used to evaluate reatment N =3), year (N = 3), date (N = 3), and 2-way(4 df) and 3-way (8 df) interaction ffectson shrub diameter and height. Repeatedfactors were years and dates within years.Analyses incorporated a first order,

autoregressive ovariance tructure mongrepeated measures. This is an alternativeto adjusting he degrees of freedom or thelack of independence mong dates as sug-gested by Milliken and Johnson 1984). Alog transformation elped stabilize vari-ances among treatments, years and datesfor diameter measures, but transformationwas unnecessary or shrub height. Singledegree of freedom contrasts were used formean separations etween treatments n agiven date. Within treatments, paired -test (2 df) was used to test for changes nshrub dimensions between adjacent dates(Snedecor nd Cochran 1967).

For response variables monitored n anannual basis (i.e., measures of standingcrop, twig length, evels of forage utiliza-tion, and cumulative number of shrubsgrazed or trampled), a split-plot analysisof variance was used to evaluate treat-ment, year, and interaction effects.Treatments 2 df) served as whole plots,with the block x treatment nteraction 4df) serving as error term 1. Years were

subplots with year (2 df) and the treatmentx year interaction (4 df) tested with theresidual error erm (12 df). This approachwas used because year effects cannot berandomized, and one is forced into aninadvertent split-plot (Cody and Smith1997). Again, f effects were significant nanalyses of variance, ingle degree of free-dom contrasts were used for mean separa-tions

Regression analyses were used toexplore and quantify relationships mongthe number of shrubs grazed or trampled(dependent ariables) nd several ndepen-dent variables. Independent variablesincluded expressions quantifying passageof time, forage availability, numbers ofcattle, pasture size, and several combina-tions of these [i.e., days grazed, AU days,area available (ha), forage available (kgand kg ha-'), stocking rates (AU ha-', AUdays ha-'), and stocking pressure kg for-age AU-', kg forage ha-' AU-', and kg for-

age AU-' day-')]. Scattergrams relatingnumbers of bitterbrush rampled o pas-sage of time suggested linear modelsmight suffice. Depictions of bitterbrushgrazed and passage of time suggested acurvilinear unction might be required.

Given a high degree of variability inherbage production mong pastures, tatis-tical significance or analyses of standingcrop and forage utilization was accepted atP < 0.10. Statistical significance in allother analyses and for mean separationswas accepted at P < 0.05. Throughout hemanuscript, umbers ollowing a + sym-

bol are standard rrors SE) of the mean.

Results

Precipitation patternsSneva (1982) established hat crop-year

forage accumulation in the region wasmost closely correlated with precipitationtotals for the previous Sept.-June period.The weather tation with the longest con-tinuous record near our study site was onthe Northern Great Basin Experimental

Range (referenced as the Squaw ButteExperiment Station in N.O.A.A. (2001)documents) some 29 km southwest and161 m lower than our study site. Meancrop-year precipitation (n = 64) for theExperimental ange s 26.1 cm, and accu-mulations for the 1997-1999 crop-yearswere 132, 196, and 106 percent of aver-age, respectively. Given the disparities nelevation and vegetation between theExperimental ange and our study site, weestimate our research plots receive about

10 cm more precipitation annually thanthe Experimental ange.

Herbaceous standing crop and for-age util zation

Herbaceous tanding crop before graz-ing averaged 652 kg ha-' and varied (P =0.05) among years but not treatments P =0.28). For the 1997-1999 sampling peri-

ods, mean herbage production was 777 (?68), 596 (? 45), and 583 (? 47) kg ha-',respectively, n early May. Given a historyof light spring use in our grazed pastures,our samples contained a substantialamount of cured material from previousgrowing seasons for our initial 1997 har-vest. Materials were not sorted, however,so we can not quantitatively addresslive:dead atios.

Grazing reatment P = 0.01) and year (P= 0.06) effects were significant or levelsof forage utilization y cattle, but the treat-ment x year nteraction was not (P = 0.34).

Mean forage utilization was 32 (? 7)% inlightly-grazed pastures and 59 (? 9)% inheavily-grazed units. Across treatments,herbage utilization y cattle averaged 5 +7, 37 + 8, and 65 + 14% or the 1997-1999trials, respectively.

Defoliation and trampling of shrubsby cattle

The number of bitterbrush rowsed bycattle during the trials differed amongtreatments (P = 0.002) and years (P =0.04), but no treatment year interaction(P = 0.11) occurred. When trials ended,an average of 14 (? 5)% of the bitterbrushwere browsed by cattle n the light-grazingtreatment, nd 62 (? 9)% were browsed nheavily-grazed astures P = 0.05). No bit-terbrush were defoliated in the ungrazedcontrols when cattle were on site (data notshown). Cattle did not initially forage onbitterbrush, ut began browsing he plantsabout days 5-6 in the heavily-grazed reat-ment and about day 8 in the lightly-grazedpastures Fig.1).

Among regressions elating he cumula-tive number of shrubs grazed (dependentvariable) o the passage of time and

vari-ous expressions of herbaceous standingcrop or stocking pressure, best fit (r2 =0.63, P < 0.001) was obtained with anexponential decay function Fig. 2) wherestocking pressure, xpressed as kg forageha-' AU-' at the close of the trials, servedas the independent variable. Approx-imately half the bitterbrush ere browsedby cattle when standing rop was reducedto about 75 kg ha-' AU-I. The rate ofbrowsing on bitterbrush lso appeared o

JOURNAL OF RANGE MANAGEMENT 57(2) March 2004 163



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90 -_ __l

~ 19970-e Light grazing0 + Heavy grazing

60

40

30

220CO) 10

0 7772 4 6 8 10 12 14 16 18 2090 -

870- 199870-

*60 -60

o-eX Light grazingA2 40 - -/ Heavy grazing

2201C,,'

2 4 6 8 10 12 14 16 18 20

90T~~~1999

60

500O 4 e0- Light grazing

430-

+ Heavy grazing~3012201

(01

2 4 6 8 10 12 14 16 18 20

Days of grazing

Fig. 1. The percent (? SE, N = 3) of bitter-brush browsed by cattle in lightly- andheavily-stocked pastures as grazing trialsprogressed in the spring of 1997-1999 onbig game winter range in southeastOregon.

25

z 20 y=aebx

e ~~~~~~a23.315 b =0.0082

2\ r2=0.63

,, 10 se est. = 5.1

.0

* .0 0

0 100 200 300 400 500

Kg forage ha-1 AU-1

Fig. 2. The relationship between the numberof bitterbrush grazed by cattle (out of atotal of 25 monitored shrubs) in lightly-and heavily-stocked pastures in southeastOregon and kg forage ha'l AU 1 duringspring stocking periods of 1997-1999.

increase when standing crop went belowthe 75 kg ha-' evel.

Grazing reatment nd year effects weresignificant P < 0.01) for trampling dam-age, but treatments responded similarlyamong years (P = 0.07). Across years, 29(? 4)% of the shrubs were trampled inlight-grazing treatments, and 55 (? 5)%were trampled under heavy-grazing. Notrampling effects were noted in controlpastures. For individual ears across the 2grazed treatments, percentages of shrubstrampled were 28 + 5, 49 + 7, and 49 +7%, from 1997-1999, respectively.

Rates of trampling damage to shrubswere well correlated with expressions ofstocking rate (AU ha-')) and time (days).With linear models and cumulative cattledays ha-' regressed against the number ofshrubs trampled, coefficients of determi-nation (r2) ranged between 0.84 and 0.86(Fig. 3). Slopes of the regression modelsdiffered (P < 0.01) among years and

increased slightly as the study advancedfrom 1997 through 1999. Only I shrub,located where the cattle frequently bed-ded, died from trampling amage.

Canopy diameter and height of bit-terbrush

With the exception of a grazing treat-ment x year interaction P = 0.33), all 3main effects (treatments, ears, and sam-pling dates), 2-way, and 3-way interac-tions had significant ffects (P < 0.05) oncanopy diameter. When the trials began n1997, bitterbrush in grazed treatmentswere approximately cm wider (P = 0.02)than bitterbrush n the ungrazed controls(Fig. 4). When cattle were removed romthe grazed pastures 20 days later, howev-er, diameters f shrubs were similar acrossall 3 treatments (P = 0.07). Subsequentspring/summer growth of shrubs in thegrazed pastures ncreased diameters by 7to 8 cm in 1997, while shrubs in theungrazed ontrols only expanded by about3 cm (P < 0.01). In both 1998 and 1999,browsing by cattle in the heavily-grazedpastures reduced (P < 0.01) the diameterof bitterbrush uch that hey were the samewidth as bitterbrush n the ungrazed on-trols. Compensatory growth occurred nthe heavily-grazed pastures n both 1998and 1999, however, and bitterbrush eregreater n diameter han ungrazed ontrols(P < 0.01) and equal to the lightly-grazedtreatment when fall dimensions wererecorded. Overwinter browsing by biggamne educed P = 0.05) shrub diametersin grazed pastures fter all 1997 measure-ments Fig. ), but big gamne adno affecton bittrbrush iameter hereafter.

Among analyses of shrub height, allmain effects (treatment, ears, and dates)were significant (P < 0.03) as were thetreatment x date and year x date interac-tions (P < 0.01). Bitterbrush eights weresimilar among treatments when the studybegan (Fig. 5), and unlike shrub diameters,browsing by cattle did not reduce heightsof bitterbrush during any of the grazingtrials. Fall and overwinter rowsing by biggame, however, did reduce (P < 0.05) theheight of bitterbrush n all treatments verthe 1997 and 1998 fall/winter periods.Light spring grazing among bitterbrushstimulated summer height growth com-pared to the other 2 treatments Fig. 5).Across years, shrubs n the lightly-grazedpastures were more than 4 cm taller (P 0.05). Means for a given treatment (column) sharing a common lower case letter betweenadjacent sampling periods are not significantly different (P > 0.05).




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Neal, D.L. 1981. Improvement f Great Basindeer winter range with livestock grazing, p.61-73. In: Proc. Wildlife-livestock elation-ships symposium. Forest, Wildlife & RangeExper. Sta., Univ. Idaho, Moscow, Ida.

Reiner, RJ. and PJ. Urness. 1982. Effect ofgrazing horses managed as manipulators fbig game winter range. J. Range. Manage.35:567-571.

Snedecor, G.W. and W.C. Cochran. 1967.Statistical methods. Iowa State Univ. Press.Ames, Iowa.

Sneva, F.A. 1982. Relation of precipitation ndtemperature ith yield of herbaceous plantsin eastern Oregon. Int. J. Biometeor.26:263-276.

Stuth, J.W. and A.H. Winward. 1977.Livestock-deer relations in the lodgepolepine-pumice region of central Oregon. J.Range Manage. 30:110-116.

Tueller, P.T. and J.D. Tower. 1979.Vegetation stagnation in three-phase biggame exclosures. J. Range Manage.32:258-263.

Urness, PJ. 1981. Livestock as tools for man-aging big game winter range in the inter-mountain west, p. 20-31. In: Proc. Wildlife-livestock relationships symposium. Forest,Wildlife & Range Exp. Sta., Univ. of Idaho,Moscow, Ida.

Vavra, M. and F. Sneva. 1978. Seasonal dietsof five ungulates grazing the cold desertbiome. In: D.N. Hyder (ed.), Proc. 1 Int.Rangeland Congress Soc. Range Manage.Denver, Colo.

Winward, A.H. and J. Alderfer-Findley.1983. Taxonomic variations of bitterbrush(Purshia ridentata) n Oregon, p. 25-30. In:Tiedemann, A.R. and K.L. Johnson comps.)Proc. Research and management of bitter-brush and cliffrose in western North

America. USDA-For. Serv., IntermountainForest and Range Exp. Sta. Gen. Tech. Rep.INT-152. Ogden, Ut.


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