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Responses of Vegetation and Livestock to Grazing Method and Combinations of Animals on Utah Summer Range Prepared by James E. Bowns and John C. Malechek

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Responses of Vegetation and Livestock to Grazing Method and Combinations of Animals on Utah Summer Range Prepared by James Bowns

Professor of Biology, Southern Utah University Extension Rangelands Specialist, Utah State University

John Malechek

Professor USU Department of Wildland Resources

Supported by the Utah Agricultural Experiment Station,

4810 Old Main Hill, Utah State University, Logan, Utah 84322-4810

Mention of a trademark name or proprietary product does not constitute endorsement by USU and does not imply its approval to the exclusion of other products that may also be suitable. Utah Agricultural Experiment Station Research Report #214 iii


Table of Contents

Introduction .....................................................................................................................1 Need for Research...........................................................................................................2 Experimental Treatments................................................................................................3 The Research Site............................................................................................................6 Methods and Procedures................................................................................................9 Results............................................................................................................................14 Conclusions and Implications: Range Response........................................................36 Conclusions and Implications: Livestock Response...................................................43 Management Implications............................................................................................45 Literature Cited.............................................................................................................. 47

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Figure 1. Relict pasture with a tall forb community that probably represents the original pre-settlement vegetation on Cedar Mountain.

Responses of Vegetation and Livestock to Grazing Method and Combinations of Animals on Utah Summer Range James E. Bowns and John C. Malechek

Introduction Mormon pioneers entered what is now Utah in 1847 and colonization soon spread throughout the area. Cedar City was settled in 1851, and livestock production, a significant part of the agrarian society, was the main source of income from meat, milk, butter, cheese, hides, and wool. By the late 1860s, the fear of Indians and wild animals had subsided, and the local residents took up homesteads in the nearby mountains. The first agriculture activity was dairying. Women and children moved to the mountains for the summer and set up dairies while the men and older boys remained in the valley and farmed. Thus, dairy cows were the first livestock to utilize these mountain ranges. Milk 1


was used mainly for making butter and cheese, which was taken to town each week or two and sold or traded for needed items. McConnell (1962) described the “top of the mountain (in 1869) as a sylvan paradise and everywhere grass and wild barley, waist high, browse and vivid wild flowers carpeted the meadows and hillsides. Compared to the arid valley below, such untouched beauty and bounteous feed were overwhelming.� Today, only a few areas resemble McConnell’s description. In approximately 1890, some prominent Cedar City cattlemen went into the sheep business by purchasing a herd of sheep from Colorado. These early sheep men built up their herds by keeping as many ewe lambs as they could and selling only the 2- or 3-year-old wethers that were driven on foot or horseback to market in Chicago or Kansas City (Jones and Jones 1972). Livestock men soon realized that sheep were ideally suited to southern Utah ranges, especially the mountain summer ranges where larkspur (Delphinium barbeyi) was common. This plant is highly toxic to cattle but is well tolerated by sheep and is considered valuable forage for them. Even today despite the declining numbers of sheep in the West, sheep are still the dominant livestock species on Cedar Mountain.

Need for Research There is little doubt that excessive sheep grazing in the early part of the 20th century and continued sheep grazing to the present time has had a dramatic impact on these Cedar Mountain ranges, as described by Bowns and Bagley (1986). Landscapes once dominated by a mix of tall native forb species now support predominantly grasses, especially in those areas now categorized as grasslands or parklands. The range livestock industry has changed, as well. Many traditional sheep operations have converted to cattle over the past 30 years for a variety of social and economic reasons. On public rangelands, the very idea of livestock grazing of any kind is often challenged on the purported basis that grazing by domestic livestock is detrimental to the ecological health of the land. Thus, the need has never been greater for range and livestock management practices that assist the rancher in surviving difficult economic times and that have the potential for, at least, minimizing potential damage to the land, or, at best, improving the ecological condition of the land while producing a valuable product. At the urging of local southern Utah ranchers and range managers, a comprehensive research program was initiated in 1979, with the overall goal of providing assistance for meeting these needs. It was a joint effort by the Utah Agricultural Experiment Station, the Departments of Range Science and Animal, Dairy and Veterinary Sciences at Utah State University, and Southern Utah University, with the cooperation of two prominent southern Utah ranching families who would provide the land for the 2


research. The research was designed to focus on two management schemes thought to have potential for the area: 1) dual-use grazing of both cattle and sheep on common land, rather than the traditional cattle-only or sheep-only style of management; and 2) deferred grazing management, rather than the season-long grazing scheme traditionally practiced in the area. Responses to the two new management practices would be measured in terms of changes in livestock production and changes in the condition of the range. The study was designed to be long-term (10 or more years duration) in order to include variation in climatic conditions, especially drought years.

The Experimental Treatments

Deferred Rotation Grazing A perceived problem with continuous grazing is that desirable plants are grazed excessively while the less-preferred plants are grazed less, or not at all, thereby creating a competitive imbalance among the various plant species present (Holechek et. al 2004). Over time, the less-palatable species dominate the vegetative community. The real problem with continuous grazing is that livestock have preferred areas for grazing, which are often the most productive parts of the range. Even under light stocking rates, these areas often receive excessive use and eventually come to be dominated by less palatable, less productive species. Dividing the range into smaller pastures and rotating the animals among them has been demonstrated elsewhere to even out distribution of grazing use over the landscape (Holechek et al. 2004). Deferred-rotation was the first specialized grazing system developed in the United States. This system was developed by Arthur Sampson in Oregon in the early 20th century (Sampson 1913). His system involved dividing the range into two pastures. Grazing on one of the pastures was deferred until seeds had matured on the primary forage species. The deferment was alternated between pastures in successive years. Research has shown that vegetation response under this system has been slightly to moderately better than continuous or season-long grazing on mountain coniferous forest ranges (Johnson 1965, Skovlin et. al 1976). Deferredrotation grazing provides a better opportunity than does continuous grazing for the preferred plants to maintain and gain vigor and for the preferred areas to recover from heavy use (Holechek et al. 2004). Despite the problems of continuous grazing, livestock production per acre of land often has been greater under that method than under various rotational schemes (Olson et. al 1999, Holechek et al. 2004, Foote et. al 1986). This is often explained by the fact that continuous grazing allows livestock to exhibit maximum forage selectivity 3


and minimizes livestock disturbance due to gathering, trailing, and rapid change in forage quality.

Dual Use Grazing by Cattle and Sheep Ranges throughout the West characteristically have been grazed by a single species of livestock, either cattle or sheep. Exceptions have been ranges in the Edwards Plateau region of Texas, where dual use grazing is the rule, rather than the exception. Research there has shown that a mix of grazers makes more efficient use of a complex plant community than a single species grazing alone, with the added benefit of increasing profitability (Merrill and Miller 1961). The fact that Texas rangelands are essentially all privately owned makes this practice more feasible than on public lands. In general, sheep and cattle prefer different forages and, where topography is a factor, use different parts of the range. Ruyle (1983) conducted a series of smallscale grazing trials on a sub-section of the study site used in the present research. He employed stocking rates considerably heavier than in the overall present study and concluded that sheep ate less grass and more forbs and shrubs than did cattle. Cattle showed a strong reluctance to browse snowberry even when the herbaceous vegetation was greatly reduced. He also found that the utilization of grasses, forbs, and shrubs in dual-use paddocks did not represent an average of the utilization by cattle and sheep each grazing alone. Cattle and sheep grazing together used more forage, especially snowberry, than calculated from single-use averages. Schlundt (1980), using similar small paddocks, quantified the disappearance of the current season’s forage biomass. He concluded that grasses disappeared in the 5:1 sheep:cow substitution ratio at the same stocking rate as the larger study and that cattle preferred grasses to forbs. He also found cattle made little use of snowberry, compared to sheep. These different dietary habits have led to the perception that grazing sheep and cattle in combination (common- or dual-use) can improve the use of some Utah ranges (Cook 1954, Bowns 1989, Bowns and Matthews 1983). Schlundt (1980) also concluded that small increases in grazing capacity could be realized by mixing the two livestock species. Cedar Mountain is predominantly private land, and sheep grazing has been the predominant livestock use since approximately the 1890s (Jones and Jones 1972). Individual land ownerships have traditionally been fenced and most have been subdivided into separate pastures. Unherded sheep have been allowed free access to these pastures and little, if any, herding has taken place for the past several decades. Cattle use on some of Utah’s high-elevation ranges has historically been restricted because of the prevalence of larkspur. However many such areas in the state are largely free of larkspur and can be productively grazed by cattle. Such is the case for the study area, so cattle grazing was considered a viable option. 4


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The Research Site The study site was located approximately 15 miles east of Cedar City, Utah, at about 8,500 feet elevation and consists of 3,236 acres of privately owned land. Soils are described as Argic Pachic Cryoborolls, fine montorillontic faim clay loam, 2-15% slope (Natural Resources Conservation Service, Draft Iron–Washington Survey Area). The geology is upper Cretaceous or the Kaiparowits formation (Hintze 1993). The study site was fenced into 18 separate pastures in order to evaluate the comparison of the traditional season-long continuous grazing with a deferred-rotation (or switchback) grazing method, and the addition of cattle, either alone, or in common with sheep. Figure 2 is a map of the pastures and treatment assignments. Figure 3 is a map of the same area showing the major vegetation types and their locations in the experimental pastures. Figure 2. Map of study site illustrating pasture layouts, grazing treatments and major roads. Arrows indicate livestock movements between the respective deferred-rotation pastures.

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Created by Clint Stonecipher May 10, 2010


Figure 3. Vegetation map for the study site.

Created by Clint Stonecipher May 10, 2010

Major Vegetation Types Vegetation types discussed in this section refer to those shown in Figure 3. Aspen (Populus tremuloides) occupies the mesic sites and may have snowberry (Symphoricarpos oreophilus) and/or a variety of grasses and forbs in the understory. Low sagebrush (Artemisia arbuscula) occupies the xeric southwest facing aspects or sites where the snow is blown off by the prevailing southwest winds during the winter. These warmer and drier sites appear to favor the xerophytic sagebrush. Oak brush (Quercus gambelii) is scattered throughout the research area and occupies habitats intermediate between aspen and sagebrush. The open parklands or grasslands are dominated by Letterman needlegrass (Stipa lettermanii) and Kentucky bluegrass (Poa pratensis) in association with numerous other perennial grasses and forbs. 7


This range had been grazed by sheep for about 80 years before cattle were added in 1979. This long history of exclusive sheep grazing had a major impact on the present-day vegetation. Bowns and Bagley (1986) compared a similar, near-by range that had been grazed by sheep with an adjacent one that had been fenced in the 1920s and sheep excluded since that time. The difference between the two areas is obvious and dramatic, even today (Figure 1). The pasture that had not been grazed by sheep is dominated by tall forbs with a mixture of grasses and a small amount of snowberry. In contrast, the area that had been grazed by sheep since about the turn of the last century is dominated by Letterman needlegrass and tarweed (Madia glomerata). The needlegrass receives light use by sheep and increases in abundance on sheep ranges. Tarweed is the least desirable plant on these ranges. It receives little or no use by either sheep or cattle and has been reported to have allelopathic effects on other plants (Carnahan and Hull 1962). The conversion of the communities from tall forbs to needlegrass–tarweed domination appears to be permanent for all practical purposes, with little or no chance that tall forbs will ever regain their historic dominance. This appears to represent the transition from a historic stable state to a new, disturbance-induced stable state, following the multiple stable states concept of Westoby et al. (1989). Some might think that the low sagebrush communities are a result of past overgrazing by sheep and that this shrub has increased as a result. However, it appears that this particular species of sagebrush occurs as the result of its topographic position on the south and southwest exposures and its tolerance of the xeric conditions that exist there. Large, dense stands of Arizona mules-ear (Wyethia arizonica) are found on heavy clay soils in the area, a phenomenon long recognized by USDA (Range Plant Handbook 1937). These stands often are closely correlated to the locations of old sheep bedgrounds and often are found along ridge tops. Sheep bedgrounds usually are devoid of perennial vegetation other than mules-ear and tarweed, and accelerated erosion may have removed the topsoil and left the B or clay horizon on the surface. However, USDA (1937) states, “Its [mules-ear’s] occurrence in distinct patches seems to be thoroughly normal due to its aggressiveness under certain soil conditions, and not at all necessarily attributable to overgrazing as many believe.” Mules-ear is now a prominent part of the landscape, and where it exists, few of the more desirable forage species are found. The most valuable shrub on the study site is snowberry. While it is not a preferred forage for cattle (Ruyle and Bowns 1985, Schlundt 1980), it is particularly palatable to sheep. When the monsoon rains arrive in late summer, sheep, in particular, increase their consumption of snowberry while reducing consumption of forbs and grasses. The local sheepmen call snowberry “hard feed.” Personal observations indicate that this shrub also provides excellent watershed ground cover, nesting cover for birds, ideal nest sites for hornets and habitat for small mammals. Aspen is the most desired vegetation type for both aesthetics and its understory plants. Grasses and forbs under the aspen canopy remain green longer into the 8


summer and appear more palatable than those in the unshaded areas. Aspen stands can be conveniently sub-classified by whether there is an herbaceous or snowberry understory. Aspen on the study site is not replaced in ecological succession by spruce-fir like the aspen at higher elevations. Rather, it is considered to be the climax vegetation type for the site. This phenomenon may be due to a shortage of effective precipitation, because on the mesic north-facing slopes, at similar elevations and on other areas off the study site, aspen is seral to spruce-fir. In recent years many aspen clones in the area have been dying and are not being replaced by suckers, the typical means of reproduction (Ohms 2003). This phenomenon is accelerating at a rapid pace. The result of this die-off is less overall aspen and more grassland or parkland on the landscape.

Methods and Procedures The study was conducted between 1979 and 1992. The first year (1979) was used to construct fences for the 18 pastures, develop permanent water sources in each pasture, construct livestock handling facilities, construct seven livestock exclosures, and establish permanently located vegetation transects for assessing vegetation change (termed trend or range trend) in each pasture and exclosure.

Treatments Grazing treatments, initiated in 1980, included sheep grazed alone, cattle grazed alone, and sheep and cattle grazed together. Each of these animal treatments was grazed under a continuous and a deferred-rotation grazing method. There were two replications of each treatment combination, yielding a total of 12 treatment/replication combinations. The rotation grazing treatments required that two pastures be grazed each year, one early in the grazing season and one late in the season. Therefore, a total of 18 separate pastures were required for the study. Timing of the rotation each year was determined by ocular evaluation of forage utilization in the initial pasture. The pasture layout, treatment assignments and the rotation scheme are illustrated in Figure 2.

Setting Stocking Rates At the beginning of this study an advisory committee consisting of the heads of the USU Departments of Animal Science and Range Science, the director of the Agricultural Experiment Station (UAES), and the UAES statistician was constituted. This committee recommended that all pastures should be stocked at levels that would result 9


in uniform grazing pressure. The initial stocking rates were then determined through consultations with local range managers from the U.S. Forest Service, the Natural Resources Conservation Service (NRCS), and local ranchers recognized for their good range management practices and conservative stocking rates (Tom Williams, personal communication 1980). Utilization of grasses on the study site was then measured during the initial year of grazing (1980) and during the subsequent 5 years (1981 through 1985). The 1980 utilization data indicated that the initial stocking rates were overly conservative and stocking rates were subsequently increased. Adjustments were also made for the inherent differences in individual pastures’ grazing capacities and for the drought of 1989-90. The ratio of sheep to cattle (five ewes with lambs equivalent to a cow and her calf) were determined through consultations of project leaders and published values in the literature (Stoddart, Smith and Box, 1975) and were subsequently verified by findings from a separate sub-study (Schlundt 1980) on the same research site.

Precipitation Precipitation data were obtained from a rain gauge located at the Southern Utah University Mountain Center. This gauge is located at nearly the same elevation (8,135 feet), and while it is 6 air miles north of the study site, it is accessible year round. Winter and spring access to the study site is precluded, first, by deep snow and, then, by muddy impassable roads, typically from December to June.

Key Species To evaluate changes in plant composition and trends in range condition, six plant species were selected as key species and monitored in alternate years for the duration of the study. These six species (four grasses and two forbs) were selected because of their value or lack of value as forage, their wide distribution, and the hypothesis that they would increase or decrease over time due to the treatment effects. Following are descriptions of these six key species and the rationale for their selection. Kentucky bluegrass (Poa pratensis) is a long-lived rhizomatous perennial considered to be entirely a European introduction by many botanists. However, its occurrence on remote meadows in areas like the Uinta Mountains of Utah and numerous other areas suggest that it must be a native species (Cronquist et al. 1977). It is highly palatable and nutritious for all classes of livestock as well as for elk and deer (Welsh et al. 2003). It is one of the first plants to green-up following summer rains and provides high quality forage late into the growing season. Kentucky bluegrass plays an important role on these ranges, and an increase in its abundance is considered desirable. 10


Letterman needlegrass (Stipa lettermanii) is an aggressive native perennial bunchgrass with very fine, tough leaves (Parker et al. 1979). It increases on ranges heavily grazed by sheep and is dominant on sheep ranges (Ellison 1954), but is a minor component on Cedar Mountain ranges where sheep have been excluded (Bowns and Bagley 1986). On this study site a decrease in this grass is considered desirable. Slender wheatgrass (Agropyron trachycaulum) is a perennial bunchgrass that grows to a height of 2.5 feet. Its forage value is good, and it is considered a high seral species and a decreaser on all range sites (Parker et al. 1979). It is considered an excellent forage species for cattle, horses, sheep, elk and deer and provides valuable cover and feed for small mammals and birds. Letterman needlegrass withstands grazing use reasonably well and serves as a good indicator of trend (Parker et al. 1979). An increase in this species is considered desirable. Mountain brome (Bromus carinatus) is a high seral, short-lived, erect, perennial bunchgrass of medium height (2 to 3 feet). It is a valuable native grass of most mountainous Utah ranges (Parker et al. 1979) and is excellent forage for cattle, horses, and elk and fair forage for deer and sheep. An increase in this grass is considered desirable. American vetch (Vicia Americana) is a highly desirable, native perennial forb that may be low growing, trailing or climbing. It is not usually very abundant, but it is highly palatable, nutritious and probably contributes to nitrogen fixation (Range Plant Handbook 1937). An increase in this species is considered very desirable. Tarweed (Madia glomerata) is a very undesirable native annual forb that secretes a sticky exudate and emits a highly objectionable tar-like odor. On the Wasatch Plateau, it was probably scarce or absent in the original vegetation and became abundant following overgrazing (Ellison 1954). It is considered an invader and has little or no forage value. There is some evidence that it produces a natural inhibitor (allelopathy), which reduces or inhibits the growth of associated desirable species (Carnahan and Hull 1962). Bowns and Bagley (1986) found that it was the most abundant forb on some sheep ranges but was scarce in the native ungrazed vegetation. A decrease in this plant is considered desirable.

Exclosures Seven small paddocks (exclosures), approximately 0.75 acres each, were fenced to exclude livestock grazing. One exclosure was placed in each of the seven vegetation types presented in Figure 3. However, three of these representing the vegetation types sagebrush, snowberry and aspen/grass were later deemed to be atypical of the areas where the majority of the trend transects were located. Therefore, in the final analysis, data from only the remaining four exclosures were used to assess species changes where livestock grazing was not a factor. 11


Vegetation Measurements Fifty-six trend transects were permanently marked with steel fence posts, and frequency of occurrence data (Hironaka 1985) were recorded for the six indicator species every second year (beginning in 1980). One hundred permanent 30 x 30-cm plots spaced regularly along each transect were read for the frequency information. Similar trend data also were collected along permanent transects within the exclosures. For analysis, the frequency data were combined by treatment. Data from the four remaining exclosures were not analyzed statistically, due to extreme variation among them with respect to their initial vegetative makeup. Above ground forage biomass (also known as standing crop) was measured as an indicator of annual forage production. Data were collected every other year but on alternate years from trend data. This was done by double sampling techniques (Pehanec and Pickford 1937) on 30 x 60 cm rectangular plots. One hundred plots were read along pace transects that ran parallel to but approximately 50 ft. distant from the permanent frequency transects. Measurements were taken after plants had achieved peak biomass. Pastures being grazed were measured first, so as to minimize effects of utilization. On the relatively few sample plots where grazing was apparent, biomass estimates were adjusted ocularly. Data are presented on a dry weight basis. Utilization was measured annually in all treatments from 1981 to 1985 and again during the drought year of 1989. Measurements were limited to perennial grasses because most perennial grass species were present in all pastures and grass is the main forage class for both cattle and sheep. The height-weight method (Cook and Stubbendieck 1986) was used. Briefly, this involved cutting representative samples of each grass species into 1- or 2-inch segments, determining the weight of each segment and then developing height-weight relationships for each species. Once these height-weight relationships were established, it was only necessary to measure stubble heights of both grazed plants and ungrazed plants on the ground. Utilization percentage was then calculated as the difference (in weight) between grazed and ungrazed plants. Heights of both grazed and ungrazed plants were measured on all perennial grass species present in thirty 15x30-cm randomly located plots in each treatment pasture. These measurements were taken at the end of grazing in a rotation pasture or at the end of the grazing season for the season-long pastures. Plots were located in “key areas� (Bonham 1989) and the same key areas were sampled each year. During 1983, 1984, 1985, and 1989 utilization was also estimated by the percentage of grazed plants method (Stoddart 1935), and the two methods were compared.

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Statistical Analysis1 For analysis, frequency data were summarized across plots on transects to construct a proportion of occupied plots for each key plant species in each year within each pasture. The effects of grazer (cattle, sheep or both) and grazing method (continuous or rotational grazing) through time on plant frequency were assessed using a generalized linear mixed model using a beta distribution with a logit link with maximum likelihood estimation implemented by the Laplace method (Smithson and Verkuilen, 2006). Pastures were the experimental units for the categorical fixed-effects factors of grazer, method and the interaction of grazer and method. Repeated measures on each pasture through time were the experimental units associated with the categorical fixed-effects factor of year. Interactions of year with all other fixed-effects terms were included. The covariance structure for the repeated measures was modeled using a first-order autoregressive structure. Each key species was analyzed separately. Data analyses used the GLIMMIX procedure in SAS/STAT, Version 9.2 in the SAS System for Windows (Copyright Š 2002-2008, SAS Institute Inc.). Data from the four pertinent exclosures were not analyzed statistically due to extreme variation among them with respect to their initial vegetative makeup.

Results Precipitation Precipitation is the driving variable for virtually all rangeland ecosystems in the West. That is to say, precipitation, or the lack thereof, largely determines production responses of the plant communities and the livestock that depend on them. It also plays a major role in the long-term trends of vegetation change or range trend (Holechek et al. 2004). The annual precipitation pattern for Cedar Mountain is presented in Fig. 4. March is typically the wettest month with an average 4.3 inches or 15% of the annual total, followed closely by February with 3.2 inches or 11.3% of the annual total. These two wet months contribute over 26% of the average annual precipitation. Summer precipitation, locally known as the monsoons, occurs in July with an average of 2.1 inches, August with 2.4 inches, and September with 1.7 inches. These three months contributed 21% of the average precipitation for the years of the study. Within that period, the average precipitation for the years of the study (1979-1992) was 30 inches, or about 6% more than the longer 22-year period. The period from 1970 until the beginning of the study (1979) was included in order to illustrate the precipitation pattern just prior to this study. Nineteen seventy-three was a very wet year (38.3 inches) followed by a very dry year in 1974 (18.2 inches). The pattern from 1970 through 1978 was more erratic than 14

This section was contributed by Ms. Susan L. Durham, Programmer/Analyst, Utah State University Ecology Center. Ms. Durham conducted the statistical analyses.

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Figure 4. Average annual precipitation (water year basis) at SUU Ranch (8,135 feet elevation). Solid horizontal line is the 1970-1992 Figure 4 average (28.3 inches). Dashed horizontal line denotes the annual average for the period of the study (1979-1992).

Precipitation (inches)

Precipitation (inches)

40 40

30 30

20 20

10 10

SUU SUURanch Ranch 1970 Average 1970– 1992 - 1992 Average 1979 Average 1979– 1992 - 1992 Average

00

1970 1970

1974 1974

1978 1978

1982 1982

1986 1986

1990 1990

1994 1994

the slightly higher and more consistent period of 1979-1988. Serious drought years of 1974 and 1977 were followed consecutively by years with greater than average precipitation. The dry period of the study (1989-1991) was more severe, but of similar duration to the 1970-1972 periods (Fig. 2). The wettest year was 1983 when 40.8 inches were recorded. This was 144% above average for the 1970 to 1992 period and 136% above the average for the study period. The driest years were 1974 (18.2 inches) and 1989 (18.8 inches). Winter precipitation, primarily as snow, results from frontal storm patterns having a southwesterly flow, while summer moisture results from high intensity convectional storms, which often cause overland water flow and soil movement. One benefit of these high intensity storms is the runoff that replenishes water in stock watering ponds.

Precipitation and Forage Biomass Variability in annual precipitation is the major factor responsible for fluctuating plant production from year to year. Table 1 illustrates the variability in aboveground forage biomass (pounds per acre, air dry) by water year (October 1 through September 30) precipitation. Average forage biomass yield was 976 pounds per acre over the seven sampling periods (Table 1). The most productive year was 1983 when biomass was 1,821 pounds per acre or 187% of the average. In contrast, the lowest production was 527 pounds of biomass per acre or 54% of average during the driest year of 1989. 15


Table 1. Forage biomass (lbs/acre) in relation to precipitation for three multi-month periods from 1979 to 1991: October – September (water year); October – May; and January – May.

Inches of Precipitation Year

Oct – Sep.

Oct – May

Jan – May

Forage Biomass (lbs/acre)

1979

37.5

34.1

18.6

1085

1981

29.0

21.9

16.9

722

1983

40.8

32.0

20.7

1821

1985

30.2

22.4

11.6

828

1987

24.9

18.9

15.0

976

1989

18.8

12.1

7.45

527

1991

20.9

16.6

11.5

866

Average

29.0

22.6

14.5

976

r

0.81

0.75

0.78

r

0.66

0.56

0.61

2

Table 2. Stocking rates in acres per animal unit month (A/AUM) rounded to the nearest acre. Year and treatment averages are carried to the nearest decimal.

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Year

Cattle Rotation

Cattle Continuous

Sheep Rotation

Sheep Continuous

Cattle/Sheep Rotation

Cattle/Sheep Continuous

Average

1980

4

4

5

4

4

4

4.2

1981

3

3

4

3

3

3

3.2

1982

3

3

4

3

3

3

3.2

1983

4

3

4

4

4

3

3.7

1984

3

3

3

3

3

2

2.8

1985

3

3

3

3

3

2

2.8

1986

3

3

3

3

3

2

2.8

1987

3

3

4

3

3

3

3.2

1988

3

3

3

3

3

2

2.8

1989

3

3

3

3

3

2

2.8

1990

4

4

4

4

4

3

3.8

1991

3

3

3

3

3

2

2.8

Average

3.2

3.2

3.6

3.2

3.2

2.6

3.2


A regression analysis relating precipitation (the independent variable) to forage biomass (the dependent variable) yielded a coefficient of determination (r2) of 0.66 when precipitation for the entire water year was considered. This finding indicates that 66% of the variability in annual forage production was attributable to amount of precipitation. Unfortunately, there is no predictive value in using October-throughSeptember (i.e., the water year) precipitation to estimate biomass production for that year because the grazing season is over before the data are available. However, it may be possible to use other time periods for predicting forage available for grazing. 75% of the precipitation occurs between October 1 and May 31, the period immediately prior to the summer growing season (and the livestock grazing season). The coefficient of determination (r2) for this period is 0.56. Similarly, 49% of the precipitation occurs between January 1 and May 31. The r2 value for this period is 0.61, a slightly better relationship than for the October through May period and nearly as good as for the entire water year. The purpose in demonstrating these relationships is to encourage a range manager with access to precipitation data to investigate similar possibilities for using linear regression equations to estimate forage biomass and, potentially, stocking rates for ranges under his/her management. It should be noted that such calculations apply only to fairly local areas and location-specific data need to be developed for specific areas, recognizing that usefully accurate predictions will not be possible for all areas.

Stocking Rates As reported in the methods section, stocking rates were adjusted after the first year of the study and again in 1990 due to the drought that began in 1989. Actual stocking rates achieved are presented in Table 2. The sheep rotation treatment had the lightest stocking rate. This light rate was mainly a result of one pasture (Pasture 9) in that treatment being vegetated predominantly by low sagebrush (see Fig. 2) with very little palatable herbaceous understory forage. Low sagebrush is unpalatable to sheep during the summer. Prior to developing pastures for this study, this location was rarely used by sheep. Another reason for this low stocking rate was that Pasture 13, also used in the sheep-rotation treatment, had vegetation predominated by grasses and very little snowberry. Snowberry is a shrub that produces large amounts of palatable forage for sheep. As indicated above, in 1990 pastures were stocked at a lower rate than in previous years because it was the second year of a significant drought. The effects of the drought had subsided somewhat by 1991, and the stocking rate was re-set to the previous levels. In 1983, pastures were stocked with the same number of animals as in 1982, but the grazing season was shortened by about one month because late snow melt prevented access to the study site until later in the summer. 17


In terms of individual pastures, the Cattle/Sheep Continuous pastures sustained a stocking rate approximately 23% greater than the mean for all pastures, reflecting a potential advantage of mixed-species grazing and somewhat more favorable forage conditions there. Other than these exceptions, stocking rate was quite uniform across most treatments and years.

Utilization The data presented in Table 3 represent utilization by weight and by percentage of plants grazed for combined perennial grasses in each pasture. For all years and all treatments the average utilization (by weight) was 59%. The highest utilization value was 66% during both 1983 and 1989. Ironically these were the wettest and driest years, respectively, for the entire period of the study. The lightest utilization was 51% in 1982. Compared to the overall average of 59%, the high of 66% was only 7 percentage units above the average and the low of 51% was only 8 percentage units lower than the average. These data, when viewed in light of the stocking rates (Table 2) suggest that grazing pressure was generally uniform among treatments and years.

Table 3. Utilization levels of all perennial grasses by percent of weight removed (% W) and percentage of plants grazed (% P).

Year

18

Cattle Rotation

Cattle Continuous

Sheep Rotation

Sheep Continuous

Cattle/ Sheep Rotation

Cattle/ Sheep Continuous

Means

%W %P

%W %P

%W %P

%W %P

%W %P

%W %P

%W %P

1981

63

54

61

66

61

55

60

1982

52

57

48

54

47

50

51

1983

59

61

73

66

65

63

71

63

59

59

66

72

66

65

1984

51

72

55

76

53

57

56

57

52

73

58

67

54

67

1985

65

64

63

64

55

60

58

52

60

65

56

54

60

61

1989

65

79

68

91

69

81

63

78

66

89

66

86

66

84

Means

59

69

62

74

58

65

61

64

58

72

58

70

59

69


Comparison of Utilization Measurement Methods Considerable work has been devoted to developing relationships between the percentage of plants grazed and utilization. The percentage of plants grazed method is simple to use in the field, once the basic relationship is determined, since all that is required is to classify each plant as grazed or ungrazed (Holecheck et al. 2004). At the utilization levels measured in this study and during the years the two methods were employed, there is a reasonably good relationship between percent utilization and percent of grazed plants. The overall relationship is 59% utilization compared to 69% of grazed plants (Table 3). The poorest agreement between the two methods was during the severe drought year of 1989 when utilization was 66% but the percentage of grazed plants was 84%. Most likely, individual plants were smaller in stature as a result of the poor growing conditions and more individual plants were grazed. Overall, however, using the grazed plant method would have produced adequate utilization estimates in most years, and measurements could have been accomplished with considerably less time and expense.

Treatment Effects Arguably the most important aspect of this study was assessment of any changes in plant composition that occurred with different grazing animals and combinations of these animals, if deferred-rotation was, in any way, superior to continuous seasonlong grazing, and how changes occurred over time. Results of the statistical analysis of the various treatment combinations on the six key species are shown in Table 4. Values shown in bold face type were considered both statistically and biologically significant. It is quickly apparent from the table that every species was affected either singly by one of the three main experimental factors, or, more commonly, by the interaction of two or all three of the factors. Rotational vs. season-long grazing (Method) was not a sufficiently potent experimental factor, acting alone, to affect any key species, while the passage of time and all of its complications (Year) affected every species. Grazing by sheep vs. cattle was a statistically significant factor for three species (slender wheatgrass, Kentucky bluegrass and American vetch). With the lone exception of mountain brome, all of the other key species showed the influence of two or all three of the factors interacting together to elicit change. The following discussion of these sundry effects is organized on the basis of the six key species and is presented in the order in which they appear in Table 4.

19


Figure 6 

Table 4. 100 Significance levels for tests of fixed-effects factors.

Factor

Agtr

Brca

Magl

Popr

Stle

Viam

Grazing Method (M)

0.6760

0.24

0.02

0.48

0.25

0.21

Grazer (G)

Frequency (%)

80

Continuous Rotation

0.0540

0.66

0.25

0.05

0.01

0.11

M*G

0.69

0.71

0.84

0.14

0.12

0.13

<0.01

<0.01

<0.01

<0.01

<0.01

0.63

0.79

20

Year (Y)

<0.01

Y*M

0.09

0

0.411982

1980

<0.01 1986

1984

1988

Year

0.60 1990

1992

Y*G

0.76

0.22

0.50

0.30

0.27

0.82

Y*M*G

0.94

0.54

0.06

0.84

0.43

0.42

Figure 5.

Figure 5 

Frequency (%) of slender wheatgrass in pastures grazed by cattle alone, sheep alone, and by both species in combination. Bars with different letter superscripts differ statistically at P = 0.11.

100

Frequency (%)

100 80

Frequency (%)

80

60 60 40 40

a

ab

b

a

ab

b

20 20 00 Cattle Cattle

Figure 6.

Sheep Sheep

Both Both

Figure 6 

Frequency (%) of slender wheatgrass in continuously- vs. rotationally-grazed pastures over the

12-year study.

100

Continuous Continuous Rotation Rotation

100

80 Frequency (%)

Frequency (%)

80

Figure 7 

60

60

40

40

2020 00

20

1980

1982

1984

1986

1988

1990

1992

1980

1982

1984

1986 Year

1988

1990

1992

Year


Slender Wheatgrass (Agtr) This was one of the three species affected by Grazer acting alone. Less of it was found with cattle grazing than with either sheep alone or cattle and sheep combined (Fig. 5). This result is consistent with the dietary preferences of the two species of grazers; cattle, with their larger mouths and gut capacity are better able than sheep to utilize a tall-statured, somewhat stemmy species such as slender wheatgrass, thereby placing more grazing pressure on the plant and potentially leading to its diminished presence on the range. Slender wheatgrass was not a particularly abundant species (frequencies generally less than 30%), so such differences in animal dietary preference could lead to potentially large impacts on the plant. Additionally, slender wheatgrass (Agtr) appeared more variable over time under continuous grazing than under rotational grazing (Fig. 6), hence the significant Year x Method interaction (Table 4). Continuous grazing during the 1990 drought appeared to be especially hard on slender wheatgrass, even though it declined under rotational grazing as well, but to a lesser extent. The periodic rest from grazing afforded by the rotational scheme seemed to mitigate somewhat the impacts of drought.

Mountain brome (Brca) Mountain brome was affected only by the passage of time (“Year” in Table 4) and will be discussed in that context in a later section.

Tarweed (Magl) This undesirable species was affected by Method as that factor interacted with both Year and Grazer (Table 4). The response can best be interpreted by looking at the three-way interaction (Table 4 and Fig. 7). Continuous grazing by sheep appeared to increase tarweed, especially during the wet years of the mid-1980s, with frequencies approaching 50% (Fig. 7), while it remained remarkable stable and relatively low (< 20% frequency) under rotational sheep grazing. In contrast, continuous grazing by cattle appeared to penalize tarweed. Responses under the combined grazer treatment appeared to reflect, again, the influence of continuous sheep grazing (Fig. 7), but at lower levels than for sheep alone. The drought of 1990 (Fig. 4) played an unquestionable role in reducing tarweed’s presence on the range, especially in the two treatments (Sheep-Continuous and Both-Continuous) where it had become most abundant during the preceding wet years. Continuous grazing by either species impacted the plant in a major way during the drought of 1990, with frequencies falling to half (or less) of the levels seen during the preceding wet period. Tarweed is a very unpalatable plant and is 21


100

Continuous Rotation

Cattle

Frequency (%)

80

Figure 7.

60

Frequency (%) of tarweed under continuous vs. rotation grazing in pastures grazed by cattle alone, 100

Continuous Rotation

Cattle

sheep alone, and both species over the 12-year study. 40 Frequency (%)

80 20

60 Cattle 1980

Cattle1982

1984

1986

1988

Continuous Continuous 1990 1992 Rotation Rotation

1988

1990

1988 1988

Continuous 1990 1992 1990 1992 Rotation

Continuous Continuous Rotation Rotation

Year

80 80 20

Frequency (%)

Frequency (%)

0 100 100 40

60 60 0 40 40

1980

1982

1984

1986

1992

Year

20 20 00 100

Sheep 1980 1980

1982 1982

1984 1984

Year

80

Frequency (%)

1986 1986 Year

60

100 100 40

Sheep

Sheep

Frequency (%)

Frequency (%)

80 80 20

60 60 0 100 40 40

Sheep 1980

1982

1984

1986

1988

Continuous 1990 1992 Rotation

1988 1988

1990 1990

1988

Continuous Continuous 1990 1992 Rotation Rotation

Continuous Rotation

Year

Frequency (%)

80 20 20 60 00 40

1980 1980

1982 1982

1984 1984

1986 1986 Year

1992 1992

Year 20

0 100 100

Both 1980

Both

1982

1984

1986 Year

Frequency (%)

Frequency (%)

8080 6060

100

Both

4040

Frequency (%)

80 2020 60 00 100 40

1982 1982

1984 1984

1986 1986 Year

1988 1988

Continuous 1990 1992 Rotation1992 1990

1988

1990

Year

80 20

Frequency (%)

22

Both 1980 1980

60 0 40

1980

1982

1984

1986 Year

1992


rarely grazed by either sheep or cattle. Thus, the fluctuations in its frequency that we observed are probably related to how grazing (animal species and method) affected the plants that were tarweedâ&#x20AC;&#x2122;s competitors, rather than grazing impacts on tarweed per se.

Kentucky bluegrass (Popr) Kentucky bluegrass, a short-statured leafy plant, was one of the three species reflecting the main effect of Grazer (Table 4), and the nature of that response varied over time. As can be seen in Figure 8, sheep-only treatments had less Kentucky bluegrass than cattle-only treatments, with the combined-grazer treatments being intermediate. As with the case of slender wheatgrass discussed earlier, this is consistent with the grazing habits of the two species. Sheep, with their small, narrow mouths and preference for leafy, low-statured plants, were probably able to place heavier grazing pressure on the palatable Kentucky bluegrass than were cattle, although the species is definitely palatable to cattle. The statistically significant Grazer x Year interaction for Kentucky bluegrass (Table 4) is depicted graphically in Fig. 9. This important forage plant increased steadily in all treatments from the beginning to the mid-years of the study, especially in the Cattleonly treatments where it reached frequencies exceeding 90%. It thereafter leveled off in the Cattle-only and Both treatments but decreased somewhat in Sheep-only treatments. The rapid build-up in the early years corresponded to the run of favorable precipitation years (Fig. 4). Kentucky bluegrass was the most abundant of all the forage species and probably provided the bulk of the diet for both sheep and cattle.

Letterman needlegrass (Stle) Letterman needlegrass presented a change over time quite unlike any of the other key species. The second-most frequent species overall, it began the study at its peak levels, but declined substantially by 1988, well ahead of the drought of 1989-90. This decline was especially prominent under both methods of cattle grazing, as can be seen in the top panel of Figure 10. The drought appeared to halt the decline and even prompt a modest increase in the plantâ&#x20AC;&#x2122;s abundance. The species also declined under both methods of sheep grazing (middle panel, Fig. 10), but the scope of change was less than for cattle grazing. Where both livestock species grazed together (bottom panel, Fig. 10), the trend for rotationally-grazed pastures appeared to reflect the cattle pattern while the continuously grazed pastures tended to reflect the sheep pattern. Letterman needlegrass has very narrow, tightly in-rolled leaves forming a crowded tuft at the base of the slender wiry culms (U.S. Forest Service 1937). These morphological characteristics may provide it with adaptations for coping with water stress and give it a 23


competitive advantage during periods of drought. Overall, study-long reductions ranged from 30% to 60% of the original amounts with cattle-grazed treatments showing the greatest declines. Recall that one of the major vegetational changes resulting from the century-long history of intensive sheep grazing of these ranges was a shift from a tall-forb dominated community to one dominated by grasses, typically with an abundance of Letterman needlegrass. From that history, one might deduce that sheep do not place enough grazing pressure on the plant to affect its presence in the plant community, whereas the results of this study suggest that cattle have some capacity to reduce its abundance.

Figure 8 

Figure 8.

Figure 8 

Frequency (%) of Kentucky bluegrass in pastures grazed by cattle alone, sheep alone and by both

Frequency (%)

species in combination. Bars with different letter at P= 0.05. a superscripts b differ statistically ab 100 80

Frequency (%)

100 100

Frequency (%)

80 80 60 60 40 40

aa

bb

ab ab

60 40 20 0 Cattle

20 20

Sheep

Both

00 Cattle Cattle

Sheep Sheep

Both Both

Figure 9.

Figure 9  Frequency (%) of Kentucky bluegrass in pastures grazed by cattle alone, sheep alone and by both  

species in combination over the 12-year study.

Figure 9  100 100

Cattle Cattle Sheep Sheep Both Both

Frequency (%)

80

60

40

Frequency (%)

100

Frequency (%)

80 80 Cattle

Sheep 60 60 Both

40 40 20 20 00 1980

1980

20

24

1982

1982

1984

1986

1984

1986 Year

1988

1988

1990

1990

1992

1992

Year 0 1980

1982

1984

1986

1988

1990

1992

Year


American Vetch (Viam) American vetch frequencies were responsive to both the species of Grazer and to the interaction Method and Grazer (Table 4). The nature of these responses is best viewed through the graph of the interaction (Fig. 11). There it can be seen that continuous sheep grazing reduced the amount of vetch on the range compared to rotational grazing by sheep or to either method of grazing by cattle. Where both species grazed incommon, no difference between grazing methods was noted (Fig. 11). American vetch is palatable to both cattle and sheep, but its decumbent, twining growth habit probably makes it more accessible to sheep than to cattle. It was not a major component of the plant community (< 20% frequency) under any treatment.

Changes Over Time: The Combined Effects of Climate, Grazing Treatments and Reduced Stocking Rate Biennial levels of the six key species, averaged over all treatment effects, is depicted in Figure 12. In addition to illustrating the significant Years effect for all species (Table 4), the figure also shows the relative abundance of the various species. Clearly, Kentucky bluegrass and Letterman needlegrass were, far-and-away, the most abundant species, and their relationship to each other changed remarkably over the course of the study. Mountain brome was the least abundant species, with the remaining three (tarweed, slender wheatgrass and American vetch) in an intermediate position. These amounts and changes are complicated to interpret because at least three major factors come into play. An obvious and large one is the variable effect of climate (mainly precipitation). The early years of the study (1979 to 1983) were abnormally wet while the latter years (especially1989-1991) were extremely dry (Fig. 4). Such extremes play a major role in vegetation structure and function (Holechek et al. 2004) Another factor is the accumulating effect of the particular grazing treatment on the vegetation over time. This might reflect a change in the species of grazer (i.e., converting from a history of sheep grazing to cattle grazing) or a change in the grazing method (i.e., converting from continuous to rotational grazing). Statistical analyses indicated that four of the six key species, namely; slender wheatgrass, tarweed, Kentucky bluegrass and Letterman needlegrass, were so-affected. This was indicated by 2- and/ or 3-way interactions of the factor(s) Method and/or Grazer with the factor Year. These responses were discussed for the individual species in the preceding section. A third factor to consider was an overall reduction in grazing intensity when the research was begun. Prior to the initiation of the study, the area has been stocked at 2.4 acres per AUM, but this was reduced to 4.2 acres per AUM in 1980, the first year of grazing under the project. This represents a 75% decrease in stocking rate in the first year. Stocking rate was subsequently increased to 3.2 acres per AUM, but even at 25


100

Continuous Rotation

Cattle

Frequency (%)

80

Figure 10.

60

Frequency (%) of Letterman needlegrass under continuous vs. rotation grazing in pastures grazed Continuous

100

Cattle by cattle alone, sheep alone, study. Rotation 40 and both species over the 12-year Frequency (%)

80 20

60 0 100 100 40

Cattle 1980 Cattle

1982

1984

1986

1988

1990 1992 Continuous Continuous Rotation Rotation

1988

1990

1988 1988

Continuous 1990 1992 Rotation 1990 1992

Continuous Continuous Rotation Rotation

Year

Frequency (%)

Frequency (%)

80 80 20 60 60 0 1980

1982

1984

40 40

1986

1992

Year

20 20 00 100

Sheep 1980 1980

1982 1982

1984 1984

Year

80

Frequency (%)

1986 1986 Year

Sheep

60 Sheep

80 80 20

Frequency (%)

Frequency (%)

100 100 40

60 60 0 100 40 40

Sheep 1980

1982

1984

1986

1988

1990 1992 Continuous Rotation

1988 1988

1990 1990

1988

Continuous Continuous 1990 1992 Rotation Rotation

Continuous Rotation

Year

Frequency (%)

80 20 20 60 00 40

1980 1980

1982 1982

1984 1984

1986 1986 Year

1992 1992

Year 20

0 100 100

Both Both 1980

1982

1984

1986 Year

Frequency (%)

Frequency (%)

8080 6060

100 4040

Both

Frequency (%)

80 2020 60 00 100 40

1982 1982

1984 1984

1986 1986 Year

1988 1988

1990 1992 Continuous 1990 Rotation1992

1988

1990

Year

80 20

Frequency (%)

26

1980 Both 1980

60 0 1980

1982

1984

1986

1992


that rate, pastures were still stocked 33% lighter than they had been under the history of continuous sheep grazing. Most likely, observed changes over time are the result of a complex combination of all of these factors, but the effect of stocking rate cannot be overlooked. Unfortunately, the design of the project did not allow for an independent analysis of stocking rate impact. However, rangeland research over a wide range of localities has consistently shown that it is one of the major factors relating to plant community response. In a review of 25 long-term grazing studies on a variety of western North American ranges, Holechek et al. (2004) reported that 92% of the studies reported a downward trend under “heavy” grazing intensity, but an upward trend in 52% of the studies under “moderate” grazing and in 78% of the studies under “light” grazing intensity. They emphatically stated: “Selection of the correct stocking rate is the most important of all grazing management decisions from the standpoint of vegetation, livestock, wildlife, and economic return.” Considering the individual key species’s responses over time, slender wheatgrass demonstrated only modest changes until the 1989 drought (Fig. 12). That event prompted a decline across all treatments to levels below the beginning 1980 average. A slight increase followed until 1992, but levels still remained at or below 1980 levels. Mountain brome was the least abundant species in all treatments (Fig. 12), with its frequency seldom more than 10% at any time. Slight annual increases were noted during the 1984-1988 period, but the 1989 drought caused declines back to the 1980 beginning levels where they remained until the end of the study. As noted previously, this species was unaffected by any of the treatments. Tarweed’s changes over the course of the 12-year study were previously discussed in relation to treatment effects. Here, by way of summary, it can be stated that when averaged over all treatments, tarweed increased from the beginning to midstudy and thereafter declined to return to initial levels (Fig. 12). These responses had strong climatic connotations: increases during wet periods and decreases during dry periods with the increases being augmented by continuous sheep grazing. Kentucky bluegrass was the most abundant of the six species studied and responded the most to the combined effects of treatments, grazing intensity, and the run of favorable precipitation years (Fig. 9). It increased steadily in frequency in all treatments until mid-study, 1986, when it leveled-off and where it remained until the end. It appeared little-affected by the 1989 drought that had reduced several of the other key species. All treatments ended the study with somewhat to substantially more Kentucky bluegrass than with which they began. In this study, Kentucky bluegrass behaved as the classic “decreaser” species (Dyksterhuis 1949), i.e., a plant species that is a component of the potential community for the area and that decreases in abundance under heavy grazing but then increases once the heavy grazing pressure is relaxed. The substantial reduction of stocking rate upon study initiation, along with the run of favorable years, apparently allowed this plant to respond according to classical range condition theory (Dyksterhuis 1949) across all treatments. 27


28


Letterman needlegrass, the second most frequent species (Fig. 12), changed over time in a manner that, like Kentucky bluegrass, suggests the overriding influence of stocking rate adjustment. It began the study in 1980 as the most abundant species (Fig. 12) but then declined (during favorable years) to a low in 1988, followed by a modest increase (during dry years) to the end of the study. These changes are consistent with the behavior of a classic “increaser” species (Dyksterhuis 1949), i.e., one that is a component of the potential plant community and that increases in abundance under heavy grazing. Increaser species usually decrease in abundance once grazing pressure is relaxed, often in concert with increases in decreaser species (e.g., Kentucky bluegrass). American vetch was generally unremarkable in its successional trajectories in the six treatments. A modest drought-induced decline was followed by an equally modest recovery, and, on average, all of the treatments ended the study with approximately the same amounts of vetch with which they began.

Changes in Range Trend Range trend is defined as the “direction of change in range condition” (Society for Range Management 1989). Measurement of range trend is a monitoring technique that is widely practiced on rangelands of the West. It can be a useful tool for judging the impact of management programs and changing weather conditions on the range resource. It is especially useful to ranchers and professional range managers who have neither the time nor resources to monitor plant community change on an annual or biennial basis as we did in this project. It, in effect, provides a series of ecological “snapshots” over time by which to monitor and judge change. Trend data tell the manager whether the range is improving in ecological condition (upward trend), declining in condition (downward trend), or is remaining static. We adapted those procedures for use in the current study to provide yet another way of viewing and interpreting project results that would perhaps be more familiar and useful to the applied range manager. Specifically, increases over time in the frequencies of the following four key species would indicate an improving (upward) range trend: slender wheatgrass, mountain brome, Kentucky bluegrass, and American vetch. Likewise, decreases over time in the following two species would also be indicative of improving range trend: tarweed and Letterman needlegrass. Ideally, trend assessments are conducted at regular points in time, generally at intervals of 5-10 years. For our purposes, we chose the mid-point (1986) and final (1992) years of the study as our time points to assess the combined effects of grazing treatments and climate on range trend. Changes in the amounts (frequencies) of our 6 key species over those two 6-year periods are summarized in Figs. 13 and 14. Clearly, all of the treatment regimes improved in range condition, some more 29


than others, and virtually all of that improvement occurred during the first half of the study (compare Figs. 13 and 14). Kentucky bluegrass increased remarkably from 1980 to 1986 in five of the six treatments (less so in SC) while Letterman needlegrass declined substantially in the two treatments (CC and CR) where cattle were the only grazer. On the negative side, the undesirable tarweed also increased in all treatments except BR, but, on-balance, a strong upward range trend was indicated, especially when considered in light of associated (though smaller) increases in most of the other desirable key species. We attribute this improvement to three interrelated factors: a reduction of stocking rate compared to the historical regime, likely improved animal Figure 11 

Figure 11.

Figure 11 

Frequency (%) of American vetch under continuous vs. rotation grazing in pastures grazed by 100

cattle alone, sheep alone and both species.

Continuous Rotation

Frequency (%)

80

60

100100

Continuous Continuous Rotation Rotation

40

Frequency (%)

Frequency (%)

80 80

20

60 600 Cattle

Sheep

Both

40 40 20 20

0 0

Figure 12 

Cattle Cattle

Sheep Sheep

Both Both

Figure 12. Frequencies (%) of six key species over the 12-year study period. The value for a particular species is the average of all treatments.

100 100

Frequency (%)

Figure 12 

Frequency (%)

80 80 60 60

Popr Stle Magl Magl Agtr Agtr Viam Viam Brca Brca Popr Stle

40 40 20 20

requency (%)

100 0

0

80

30

60

1980 1980

1982 1982

1984 1984

1986 1986

1988 1988

1990 1990

1992 1992

Year Year

Popr Stle


distribution due to smaller pastures, and a multi-year run of favorable precipitation that began in 1978 and extended to 1987 (Fig. 4). In terms of individual treatments, improvement in the Sheep Continuous treatment was disappointing, considering that tarweed apparently increased more than Kentucky bluegrass and that Letterman needlegrass decreased only slightly. There was an increase in slender wheatgrass, but this species is a relatively small contributor to the overall forage base on Cedar Mountain. The latter half of the study presented a markedly different picture of range trend than did the first half (Fig. 13), a picture doubtlessly darkened by a run of dry years (including a significant drought) that was almost the figurative opposite of the first half in terms of precipitation (Fig. 4). While one or both of two desirable key species, slender wheatgrass and mountain brome, indicated declines in all treatments, the two undesirable key species, tarweed and Letterman needlegrass, also showed declines. Kentucky bluegrass and American vetch also suggested declines, but these were generally so small as to be practically unimportant. Changes less than +/- 5 frequency units are probably not meaningful in the practical sense. Therefore, viewed in the context of the large changes that occurred in the first half of the study, the scale and nature of changes during the second half suggest to us a period of relatively stable range trend for all treatments, even though two or three of the desirable species appeared to decline somewhat. Interpretation of range trend data must be considered in a fairly broad and subjective light. For a variety of reasons, plant species do not typically act in concert with our attributions of “desirable” or “undesirable” status. Desirable key species may increase under favorable conditions, suggesting improving trend, but these same conditions may also favor the undesirable species, as well (e.g., increases of both Kentucky bluegrass and tarweed during the 1980-1986 period). Likewise, undesirable species may decrease for various reasons, but often the desirable species decrease as well (e.g., decreases of mountain brome and slender wheatgrass, along with decreases of tarweed and Letterman needlegrass during the 1986-1992 period). Moreover, assignment of cause and effect due to some treatment is always complicated by the overlay of variable climatic conditions, as we saw in the two halves of this study (an abnormally wet period followed by an abnormally dry period). The picture is further complicated by the historically contingent nature of plant communities (Swetnam and Betancourt 1998). What we see today is always partly the result of what happened 1, 2, 5 years, or even decades ago. Therefore, the proper application and interpretation of range trend as a monitoring tool must include an element of the “art” as well as the science of range management. Having stated these qualifications, we are nonetheless confident in asserting that all treatments experienced a significant improvement in range condition (upward range trend) over the course of the 12-year study. This can be seen in Figure 15, which shows the difference in frequency values between the first (1980) and last (1996) years of the study. The continuously grazed sheep treatment showed the least improvement. 31


Figure 13. Range trend (change in frequency values) during the first half of the study (1980 to 1986). Figure 13 Range Trend, 1980-1986 40

Change in Frequency Values

30 20 10 0 -10

SC

SR

CC

CR

BC

BR

Agtr Brca Magl Popr Stle Viam

-20 -30 -40

Grazing Treatments

Figure 14. Range trend (change in frequency values) during the second half of the study (1986 to 1992). Figure 14 Range Trend, 1986-1992

Change in Frequency Values

40 30 20 10 0 -10 -20

SC

SR

CC

CR

-30 -40

32

Grazing Treatments

BC

BR

Agtr Brca Magl Popr Stle Viam


Figure 15. Range trend (change in frequency values) over the entire study period (1980-1992). Figure 15 Range Trend, 1980-1992

Change in Frequency Values

40 30 20 10 0 SC

SR

CC

CR

-10

BC

BR

Agtr Brca Magl Popr Stle Viam

-20 -30 -40 Grazing Treatments

Specifically, it showed the smallest increase in Kentucky bluegrass, one of the least reductions of Letterman needlegrass, the largest remaining amount of tarweed, and suggestions of a reduction in American vetch. It showed no change in mountain brome or slender wheatgrass. Other than a 33% lower stocking rate and smaller pastures, this is the treatment that most resembled the way sheep were managed on the site for approximately 80 years prior to the study. It is much less clear which of the remaining five treatments showed the most improvement in range condition. As discussed earlier, the relative changes in plant species abundance do not move in concert with our ideas of their desirability. The treatments that elicited the greatest increase in Kentucky bluegrass (e.g. CR) and the greatest decrease in Letterman needlegrass (e.g., CC) deserve attention, considering that these were, by far, the most abundant species on the range and the most and next-to-least valuable, respectively, from the grazing value point of view. Yet, all species considered, these differed so little from the remaining three treatments, no compelling argument for â&#x20AC;&#x153;best treatmentâ&#x20AC;? can be made in terms of improved range condition. Mountain brome effectively ended the study at the same level of frequency where it began in 1980 in all treatments. Considering this, along with its relative rarity in the plant community, it would not be an appropriate key species for future studies nor for use as a trend indicator in applied management situations. 33


American vetch tended to decrease in treatments grazed only by sheep, and, excepting the CR treatment, increase in cattle-grazed and cattle-sheep-grazed treatments. These changes were small (< 10 frequency units), however. Finally, slender wheatgrass decreased in all but the SC treatment, but, again, these changes were small.

Exclosures Exclosures are typically used in grazing studies as a point of reference for comparison of grazed treatments to the ungrazed situation. Often, as in the case of this study, they represent a release from grazing instead of a historically ungrazed situation. This is because most grazing studies are implemented on rangelands that have a history of some kind and amount of livestock grazing up to the point of research initiation. This considered, their interpretive value is limited. Figure 16 shows the successional pathways of the six key species within four separate exclosures that were located in representative areas of the treatment pastures. Clearly, there were major differences among the four exclosures in the beginning amounts of all key species except mountain brome. This precluded using them as replicates and pooling their data for discussion purposes and also nullified any meaningful statistical analysis of them. Therefore, the following interpretation is subjective, but it offers some insights into how the key species responded to climatic changes over the course of the study. Two species, Kentucky bluegrass and Letterman needlegrass, exhibited roughly similar trends among the exclosures and patterns that were generally reflective of how the two species behaved in the treatment pastures. Kentucky bluegrass initially increased sharply in the three exclosures where its beginning frequency was less than 80%, and the smaller the initial amount, the greater the ensuing increase. This was likely in response to the combined effects of release from grazing and favorable precipitation. It then plateaued and remained at a high level (>90%) of frequency (despite the drought) throughout the remaining years of the study, similar to the treatment pastures. Letterman needlegrass exhibited quite the opposite response, declining at an increasing rate until the 1989-1991 drought period, when it rebounded and increased until the studyâ&#x20AC;&#x2122;s conclusion. As discussed in the previous section on changes in key species over time, this plant species has morphological characteristics that probably contribute to its drought hardiness, and without the grazing pressure (especially by cattle) it experienced in the treatment pastures, it was able to increase during the dry period that extended from 1989-1992. Mountain brome was notable for its lack of response to any environmental or treatment variable. It began and finished the study at very low levels of frequency with essentially no change in between. 34


Figure 16. Frequencies (%) of the six key species in four grazing exclosures over the study period (1980-1992). Agtr designates slender wheatgrass; Brca, mountain brome; Magl, tarweed; Popr, Kentucky bluegrass; Stle, Letterman needlegrass; and Viam, American vetch.

Figure 16

Figure 16

Brca

Agtr

Frequency (%)

Frequency (%)

80 75

1 2 3a 3a 6

Agtr

75

40 50

50

50 50

25

25 25

0

0 0

20 25

00

00

Magl Brca Magl

1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992

Frequency (%)

Frequency (%)

75

Popr

75 50

80 1983 1986 1989 1992 80 1983 Year 1986 1989 1992 Year

50 25 25 25

Stle

100 100

Stle Viam

Popr 75 75

50

50 50

25 25 25

25 25

20

80 75 Frequency (%)

Magl

40 50

0 0 0 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 Stle Year 100 100 Stle 100 Viam

Popr

1980 1983 1986 1989 199 1980 1983 1986 1989 199

50

40 50

0

Stle

80 75

Brca Magl

Popr

75

20

80 1983 1986 1989 1992 80 1983 1986 1989 1992

100 100 100 100

Frequency (%)

75

80 75

100 100 75 75

40 50

20 25

100 100 100 100

Agtr Brca

Agtr Brca

80 75

1980 1983 1986 1989 1992 1980 1983 1986 1989 1992

1 2 3a 6

1 2 3a 6

Frequency (%)

100 100

100 100 100

0 0 0 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 Year 1989 1992 Viam Year 100 100 Viam 0

0 0

1980 1983 1986 1989 199 1980 1983 1986 Year 1989 199 Year

80 75

75 40 50

40 50

50 20 25

20 25

25 00

0

0 0 1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 1980 1983 1986 Year Year 1989 1992 Year

1980 1983 1986 1989 1992 1980 1983 1986 1989 1992 Year Year

35


Tarweed varied extremely in presence in the four exclosures (Fig. 16). In the two where it was initially abundant (>50% frequency), the prevailing trend was one of major decrease in frequency from mid-study until the end. This roughly corresponded to the climatically dry part of the study period (Fig. 4). In contrast, in the two exclosures where it was relatively infrequent (<10%) initially, it persisted throughout the 12 years in a low but steady amount. These successional changes are consistent with the classification of tarweed as an invader species in the high elevation aspen-tall forb plant community (Ellison 1954). With protection from grazing or under properly managed grazing (e.g., correct stocking levels, rotational grazing), it declines in abundance. American vetch also varied greatly in its initial amounts (Fig. 16), ranging from rare (approximately 3% frequency) in two of the exclosures to a high of almost 50% in one of the others. Recall that this species averaged about 12% initial frequency in the treatment pastures (see Fig. 12). The only consistent pattern among the four exclosures was a decline in response to the 1989-1991 drought, followed by an increase in 1992 when precipitation was nearer normal. The extent of the various changes over time appeared roughly related to the amounts of American vetch present, with the largest fluctuations occurring in the exclosures with the most of that species. Slender wheatgrass exhibited no obvious pattern in any of the four exclosures, although it varied more over time in two of the exclosures than did mountain brome, the other non-responsive species. This species appears more subject to influence by cattle grazing than by other factors. Recall that there was statistically less slender wheatgrass in Cattle-grazed treatments than Sheep-grazed treatments, i.e., a significant effect for Grazer in the treatment pasture data analysis (Table 4). Moreover, there was not the release-from-grazing response in the exclosures that would have been expected had the historical heavy sheep grazing been suppressing the species. Curiously, in only one of the exclosures did slender wheatgrass show the characteristic decline due to the1989 drought.

Conclusions and Implication: Range Response

36

1. Desirable changes in range trend where cattle grazed ranges traditionally grazed by sheep indicated that changing from a sheep to a cattle operation is feasible from the range improvement standpoint. 2. Grazing cattle in combination with sheep is also a viable option on this kind of rangeland where there is a diversity of vegetation and range sites. Such multi-species grazing better utilizes all three functional groups of plants (grasses, forbs, and shrubs) and all parts of the range (Cook 1954, Bowns and Matthews 1983, Ruyle and Bowns 1985). 3. Rotational grazing for either sheep or cattle grazed alone is probably not a justifiable means of improving range condition when the additional costs of fencing, water development, etc. are considered.


4. Continuous grazing by sheep (alone or with cattle) seems to favor tarweed. Otherwise, the plantâ&#x20AC;&#x2122;s abundance on the range appears to be largely a function of climate, being favored by wet years. 5. Letterman needlegrass appears highly responsive to stocking rate, species of grazer, and climatic factors. It will decline under no grazing and under proper stocking of either species of grazer, but especially under properly stocked cattle grazing. It appears to be favored by dry years.

Livestock Performance The livestock production part of the study was terminated in 1990, 2 years earlier than the vegetation response component of the project. However, the original grazing treatments and stocking regimes were continued through to 1992, as discussed earlier. Subsequently, the livestock production component of the project was published in a detailed scientific paper in 1999 (Olson et al. 1999). The highlights of that publication are summarized in the following pages in order to present a comprehensive overview of the entire project for this report. An oft-stated objective of specialized grazing methods, such as deferred rotation grazing, is to increase animal production (Stoddart, Smith and Box 1975). Likewise, concurrent grazing a single unit of land with more than one species of animal is expected to improve animal performance, carrying capacity, and range condition and productivity (Nolan & Connolly 1977, Walker 1994, 1997). However, the real livestock production benefits from either of these practices are far from certain. Considerable research effort has been expended over the past 60 or more years on various specialized grazing methods. Findings from these projects have been summarized periodically in comprehensive literature reviews (e.g. Driscoll 1967, Pieper 1980). They strongly indicate that these specialized grazing methods (including deferredrotation) decrease or have no effect on animal performance in the majority of cases, with relatively few instances of a specialized grazing method improving animal performance (Olson et al. 1999). Holechek et al. (2004), in a recent review, showed that specialized grazing methods generally give either modest (10% to 30%) or no increase in grazing capacity over season-long or continuous systems. An even more recent â&#x20AC;&#x153;synthesis paperâ&#x20AC;? that covered some of the same studies covered in the Holechek (2004) review, plus others, Briske et al. (2008) reported that plant production was equal or greater under continuous grazing compared to rotational grazing in 20 of 23 experiments they analyzed. Similarly, livestock production per head was equal or greater under continuous grazing in 35 of 38 cases, and, on a per-acre basis, in 27 of 32 cases. Much less research attention has been given to multi-species grazing, especially on western rangelands. Work done on cultivated pasture situations (e.g., Nolan and Connolly 1977) indicates that increased animal production is feasible by grazing two or more species of livestock together. The benefits would be expected to be even greater

37


on diverse rangeland landscapes, such as Cedar Mountain, where animal-specific differences in diet selection and grazing distribution can be exploited to obtain more uniform utilization of the entire pasture resources (Bake & Byington 1986). However, despite these real and hypothesized benefits, surprisingly little research has been done on this topic.

Methods Cooperating producers provided the livestock, and the same cow herd was used throughout the study. Cattle breeds were typical of commercial Intermountain ranch operations and included Herefords and crosses of other breeds, mainly Angus and Simmental, on Herefords. Calves were born in February or March and weaned after the livestock were removed from the study site, usually in mid-September. Sheep were provided initially by a Utah State University herd and by a local woolgrower later in the study. Lambs were born in April and weaned in mid-September. All livestock resided on desert rangeland or farmland when not on the study site, as is typical for ranching operations in this region (Olson et al. 1999). All animals (cows, calves, ewes, and lambs) were weighed individually at each yearâ&#x20AC;&#x2122;s initiation of grazing on the research site (mid-June), again at mid-season when animals were rotated between pastures in the rotational grazing scheme, and finally, upon termination of the grazing trials in mid-September.

Results Livestock production responses to the treatments are summarized in Table 5. Multi-species vs single-species grazing. Calf average daily gain (ADG) was statistically greater over the entire season when cattle were grazed alone rather than with sheep, although the difference was very small. This difference was due primarily to higher ADG by calves during the first half of the grazing season. Lambs, on the other hand, gained more per day when sheep grazed with cattle than when sheep grazed alone. This was the case for both mid-season and final weights. Cow ADG was not affected by species mixture. In contrast, ewe ADG was greater when grazed with cattle than when grazed alone. Ewes with cattle weighed more at both the mid-season and final weigh dates (Olson et al. 1999). These differences in performance response by sheep and cattle may be because of histori cal sheep grazing that had shifted the plant community from forb to grass dominance (Bowns and Bagley 1986). The relative decrease in sheep numbers per acre in the 38


39


multi-species treatment (compared to the Sheep-only treatment) resulted in decreased intra-specific competition for forage desired by sheep. This allowed the sheep grazing with cattle to graze more selectively (Olson et al. 1999) and, presumably, consume a more nutritious diet. Given the historic change in plant community make-up from forbs to grasses, the relative abundance of forage preferred by cattle was much greater in both treatments, so their ability to select a nutritious diet was not as greatly influenced by the animal species mixture. These results agree with the published literature, in that sheep performance is typically increased by grazing with cattle, but cattle responses, if any, have been mixed and usually smaller in magnitude than sheep responses (Nolan and Connolly 1977, Walker 1994, 1997). Walker (1994) also indicated that sheep appear to be more competitive than cattle in mixed herds because sheep are better able to select desired vegetation and can graze closer to the ground. The presence of snowberry, a sheeppreferred shrub, may have also contributed to the sheep advantage. Rotational versus season-long grazing. Overall, calves gained more under season-long rather than deferred-rotation grazing. Again, these differences were very small and are probably not biologically or economically important, despite their statistical significance. Lamb ADG, on the other hand, was not affected by grazing method. Lamb mid-season weights were greater under season-long grazing, but the difference disappeared by market time (Olson 1999). Cow weights were not affected at any time by grazing method. Season-long, ewes gained slightly less than one-tenth pound per day, and their total gain was unaffected by the grazing method. However, considerable, and probably important differences were observed when the two halves of the grazing were considered separately. Gains were relatively large (about one-third pound per day) and similar between the two treatments during the first half of the grazing season. During the second half, rate of gain was much reduced, but it was more than 2 times greater under deferred-rotation grazing (0.10 lbs/da) than under season-long grazing (0.04 lbs/da). Olson et al. (1999) assert that this late season difference may have important reproductive consequences. Improving nutritional status as evidenced by increasing body weight immediately before the breeding season can be important to increased fertility in ewes (Dunn and Moss 1992). Therefore, on the whole, instituting deferred-rotation grazing in a mixed-species system may benefit the sheep flock (improved ewe nutritional status at breeding) at the expense of the cattle herd (reduced calf weaning weights) (Olson et al. 1999). Extensive reviews of grazing methods comparisons by Driscoll (1967), Pieper (1980) and Briske et al. (2008) indicate that grazing methods have no effect or are detrimental to livestock performance in the majority of cases. Many range scientists (Launchbaugh et al. 1978, Pieper 1980, Kothmann 1980, among others) have acknowledged that most specialized grazing methods have been developed to improve range 40


Table 5. Livestock production per animal and per acre for two grazing methods and three livestock species assignments.

Grazing Method

Livestock Species

Production Variable (pounds)

Seasonlong

Deferredrotation

Multispecies

Cattleonly

Sheeponly

Calf ADG

2.3b

2.2a

2.2a

2.3b

Lamb ADG

0.53

0.53

0.55b

0.51a

Cow ADG

1.30

1.28

1.30

1.30

Ewe ADG

0.18

0.20

0.20b

0.18a

Progeny per acre

14.5

13.2

15.8b

10.0a

15.8b

Dams per acre

5.2

5.3

6.0b

5.7b

4.2a

Total (dams + progeny) per acre

19.7

18.6

21.8b

15.7a

20.2b

a,b

Within a row and ANOVA effect, means lacking a common superscript letter differ (P<0.05).

vegetation characteristics with little concern for the effect on animals. This study also provided mixed results. The net effect, however, was that there was neither a distinct advantage nor disadvantage across both species of livestock (Olson et al. 1999). Year Effects. Calf ADG increased across years during all weigh periods. This response may have partially been due to genetic improvement in the cowherd over time. However, statistical interactions indicated that it was modified by treatments. There was no trend across years under season-long grazing but a linear increase under deferred-rotation grazing. Calves gained slower under deferred-rotation in the early years but improved to be comparable to season-long grazing during the remainder of the study. Calf ADG increased over years both with and without sheep. Again, these differences are quite small and are probably unimportant in the practical sense, despite their statistical significance. Nutritional status (hence weight) of mature cows varied over years with forage conditions, as opposed to the increase in calf ADG over time. Cow ADG was particularly high in the record-setting wet year of 1983 and particularly low in 1990, the second consecutive year of severe drought (Olson et al. 1999). Lamb ADG also varied among years, but lamb performance did not show the same linear time-related increase as calf performance. Ewe performance also appeared to respond to precipitation conditions, but differences among wet and dry years were not as dramatic as with cows (Olson et al. 1999). 41


Production per unit of land. Multi-species grazing affected production per acre of progeny, dams, and combined progeny and dams, but in slightly different ways (Table 5). Production of progeny only and progeny plus dams was similar for multi-species and sheep alone at 16 pounds per acre for progeny and about 21 pounds per acre for progeny and dams combined. However, production was considerably less with cattle alone: 10 pounds per acre for calves and 15.7 for calves and cows combined. When dams alone were considered, production by ewes was considerably less at 4.2 pounds per acre compared to about 6 pounds per acre both for cows alone and cows plus ewes under multi-species grazing. Grazing method did not affect production per acre by any age group (Table 5) (Olson et al. 1999). Production per unit of land provides a measure of a systemâ&#x20AC;&#x2122;s economic and biological capability. Use of mixed species or sheep grazing should promote the greatest economic return to investment in land. In addition, the evaluation of biological productivity per unit land should include both progeny and dams. The two livestock species displayed different responses in terms of how forage nutrients were converted into weight gain by progeny versus dams. Sheep appear to partition a greater amount of forage nutrients into lamb growth through milk production by the ewe (Olson et al. 1999, Matthews et al. 1986) while cows partition a larger amount into their own body reserves. When the level of production by progeny and dams together is considered, the relatively large weight gains by cows was masked in the multi-species treatment by the high rate of lamb growth and the overall high level of growth of progeny compared to dams (Olson et al. 1999). Differences among years, primarily because of weather conditions, were large. For example, production by progeny (lbs/acre) was 60% greater in the best year than the poorest year (Olson et al. 1999). In this regard, results from this study re-confirm findings of many (indeed, most) other grazing studiesâ&#x20AC;&#x201D;the vagaries of weather often overshadow even the largest of treatment effects. This fact should be kept clearly in mind when viewing published results of short-term (e.g., less than 5 years) grazing studies.

42


Conclusions and Implications: Livestock Response Conversion of this rangeland type from historical sheep grazing to mixed species grazing would probably provide a small improvement in rate of weight gain by lambs and ewes. This would yield similar production per unit land of marketable product (progeny) but increased production per acre by dams (Olson et al. 1999). Other potential benefits might include reduced economic risk by diversification of enterprises and improved cash flow by marketing of multiple products (Walker 1994), reduced loss of sheep to predators because of cow presence, and reduced parasite loads (Baker and Byington 1986). However, total conversion from sheep to cattle does not appear advisable for this kind of rangeland. While cows and calves performed similarly or slightly better when alone, production per unit land was reduced with cattle only compared to sheep only or mixed species grazing. Tall larkspur is also common in this vegetation type, posing potential toxicity risk for cattle. However, because sheep are more resistant to larkspur poisoning, their grazing of larkspur under mixed species grazing may decrease cattle poisoning (Olson et al. 1999). Conversion from historical, continuous grazing to deferred-rotation grazing appeared appropriate for a sheep-only or mixed-species enterprise, primarily because of the improvement in ewe nutritional status shortly before breeding. This appeared to offset reduced calf ADG under deferred-rotation grazing using mixed species. However, if this resource were converted to a cattle enterprise, continuous grazing would be superior because it allowed greater calf performance (Olson et al. 1999).

General Summary and Conclusions A 12-year livestock grazing study on Cedar Mountain in southern Utah compared the following livestock species and combinations of species managed under both season-long and rotational grazing management schemes: 1) season-long grazing by sheep (the traditional grazing management approach for the area); 2) season-long grazing by cattle; 3) season-long grazing by sheep and cattle grazing together; 4) deferredrotation grazing by sheep; 5) deferred rotation grazing by cattle; and 6) deferred-rotation grazing by sheep and cattle grazing together. The time period covered by the research, 1980-1992, included average and above-average precipitation during the first 6 years and a major 3-year drought during the last 6 years. Responses to the treatments of both vegetation and livestock were measured.

43


Range Condition Range trend, measured as changes over time in six indicator plant species, improved under all treatments, as well as in ungrazed reference areas (exclosures). However, the least improvement was under season-long grazing by sheep, the treatment representing the traditional grazing practice for the area. Subtle differences were noted among the key species for the remaining five treatments, but no definitive advantage could be attributed to any single treatment as being superior for inducing range improvement. Essentially all of the range improvement occurred during the first 6 years, probably as the combined result of highly favorable soil moisture conditions, a 33% reduction in the historical stocking rate for the area, and, perhaps, fencing the range into smaller pastures thereby improving animal distribution. Even though range trend declined slightly in all treatments during the latter half of the study, undoubtedly a result of the drought, the overall, 12-year change in range condition was highly positive. Notable changes among the key species included substantial increases in the desirable Kentucky bluegrass in all treatments except season-long sheep grazing. It increased rapidly during the initial 6 years and then plateaued for the remainder of the study, remaining unaffected by the drought. A major and sustained decline in the undesirable Letterman needlegrass was seen in all treatments as well as in the ungrazed exclosures until the drought of 1989-1991 when it increased but still remained well below its initial levels of the early 1980s. It decreased the most in the two treatments where only cattle grazed. The undesirable tarweed initially increased, especially under continuous sheep grazing, and probably in response to favorable growing conditions during the 1980-1986 period. However, it subsequently declined with the onset of dry years. The remaining three key species were less abundant (< 20% frequency) and changed comparatively little in any treatment. However, all were noticeably reduced in abundance by the drought. Slender wheatgrass was reduced in frequency by cattle grazing and by continuous grazing during drought, but these changes were relatively small.

Livestock Production Several statistically significant, treatment-related effects were found for livestock production, but most were so small as to be biologically and economically unimportant. For example, calves gained faster when cattle grazed alone rather than in mixed herds with sheep, but in contrast, lambs gained faster in mixed herds than in sheep-only herds. Gains by both cows and ewes were unaffected by animal species combinations. Production expressed on a per-acre basis for progeny (calves and lambs) was measurably greater by grazing sheep alone (16 lbs/acre) or sheep with cattle (16 lbs/acre) than by cattle alone (10 lbs/acre). The same pattern held for total production, i.e., progeny plus dams. 44


Management Implications Several findings from this research can have immediate and practical application to livestock grazing management on high-elevation aspen parkland ranges in southern Utah and on similar lands in adjacent states. These may be summarized as follows: • Stocking rates approximating 3.2 acres per animal unit month should result in utilization levels of around 60% on the dominant forage (grass) species. These levels should result in an upward trend of range conditions dur- ing favorable precipitation years. Downward adjustments to around 4 acres per animal unit month may be necessary during severe drought years in order to maintain a stable trend through the drought. • Stocking at these levels should maintain stable plant communities dominated by Kentucky bluegrass, with lesser amounts of mountain brome, slender wheatgrass, American vetch, as well as the less desirable Letterman needlegrass and the undesirable tarweed. It is tempting to speculate that these plant communities have crossed an ecological threshold due to their long history of heavy sheep grazing and will not quickly revert to the pre-settlement state of tall native forb domination, even with total exclusion of livestock grazing. • From the standpoint of range improvement, the greatest gains can be expec ted from some grazing management approach other than season-long sheep grazing. However, economic factors must be considered in any such change. • Total conversion from sheep to cattle does not appear advisable from the live stock production point of view. • Multi-species grazing would be appropriate for both range improvement and optimal livestock production, but individual ranch objectives and agency constraints on public land permits must be considered. • Deferred-rotation grazing would be an acceptable practice for both range improvement and sheep performance, but, considering the cost factors involved (e.g., additional inputs of labor and capital improvements such as fencing and livestock water developments), a careful case-by-case analysis should be done before implementing the practice. First consider ation should be given to assurance of proper stocking rate.

45


46


Facing Page: Jim Bowns and John Malechek.

Literature Cited Baker, F.H. and E.K. Byington. 1986. Enhancing production of ruminant species through multispecies grazing systems. Prof. Anim. Sci. 2: 9-14. Bonham, C.D. 1989. Measurements for Terrestrial Vegetation. John Wiley & Sons. New York City, NY. 338 p. Bowns, J.E. 1989. Common use: better for cattle, sheep and rangelands. Utah Sci. 50: 116-123. Bowns, J.E. and C.F. Bagley. 1986. Vegetation responses to long-term sheep grazing on mountain ranges. J. Range Manage. 39(5): 431-434. Bowns, J.E. and D.H. Matthews. 1983. Cattle grazing with sheep: a plus for rangelands and production. Utah Sci. 44(2): 38-43. Briske, D.D., J.D. Derner, J.R. Brown, S.D. Fuhlendorf, W.R. Teague, K.M. Havstad, R.L. Gillen, A.J. Ash, and W.D. Willms. 2008. Rotational grazing on rangelands: reconciliation of perception and experimental evidence. Rangeland Ecology and Management 61: 3-17. Carnahan, G. and A.C. Hull. 1962. The inhibition of seeded plants by tarweed. Weeds. 10: 87-90. Cook, C.W. 1954. Common use of summer range by sheep and cattle. J. Range Manage. 7: 10-13. Cook, C.W., and J. Stubbendieck. 1986. Range research: basic problems and techniques. Society for Range Management, Denver, CO. 317p Cronquist, A., A.H. Holmgren, N.H. Holmgren, J.L. Reveal and P.K. Holmgren. 1977. Intermountain flora. Vascular Plants of the Intermountain West, U.S.A. Vol. 6. The Monocots, Columbia University Press. New York. 584 pp. 47


Driscoll, R.S. 1967. Managing public rangeland: effective livestock practices and systems for national forests and national grasslands. USDA AIB 315. Washington, DC. Dunn, T.G. and G.E. Moss. 1992. Effects of nutrient deficiencies and excesses on reproductive efficiency of livestock. J. Anim. Sci. 70: 1580-1593. Dyksterhuis, E.J. 1949. Condition and management of range land based on quantitative ecology. J. Range Manage. 2:104-115. Ellison, L. 1954. Subalpine vegetation of the Wasatch Plateau, Utah. Ecol. Monog. 24: 89-184. Hintze, L.F. 1993. Geologic history of Utah. A Field Guide to Utahâ&#x20AC;&#x2122;s Rocks. Brigham Young University. 202 pp. Provo, Utah. Hironaka, M. 1985. Frequency approaches to monitor rangeland vegetation. Symp. on use of frequency and for rangeland monitoring. W.C. Krueger, chairman. Proc. 38th Annual Meeting, Soc. for Range Manage., Salt Lake City, UT. 84-86. Holecheck, J.L., R.D. Pieper, and C.H. Herbel 2004. Range management principles and practices. 5th Ed. Pearson Prentice Hall. New Jersey. 607 pp. Johnson, W.M. 1965. Rotation, rest-rotation and season-long grazing on a mountain range in Wyoming. U.S. Dept. of Agric. For. Serv. Res. Pap. RM-14 Jones, Y.F., and E.K. Jones. 1972. Lehi Willard Jones 1854-1947. Woodruff Printing Co., Salt Lake City, Utah. Kothmann, M.M. 1980. Integrating livestock needs to the grazing system, P 65-83. In: K.C. McDaniel and C. Allison (eds). Proc. Grazing Management Systems for Southwest Rangelands Symp. Range Improvement Task Force. New Mexico State University, Las Cruces, N.M. Launchbaugh, J.L., C.E. Owensby, F.L. Schwartz, and L.R. Corah. 1978. Grazing management to meet nutritional and functional needs of livestock, p. 541-546. In: D.N. Hyder (ed), Proc. 1st Int. Rangeland Congr. Soc. Range Manage. Denver, Colorado.

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Matthews, D.H., W.C. Foote, R.L. Hurst and J.E. Bowns. 1986. Response of cattle and sheep under various grazing systems on high elevation summer ranges. The Prof. Animal Sci. 37: 252-254. McConnell, G. 1962. Pioneer dairying. Cedar City Public Library. 11 pages Mimeo. Merrill, L.B. and J.E. Miller. 1961. Economic analyses of year-long grazing rate studies on Substation No. 14, near Sonora. Tex. Agr. Exp. Sta. MP-484. Nolan, T. and J. Connolly. 1977. Mixed stocking by sheep and steers â&#x20AC;&#x201C; a review. Herb. Abstr. 47: 367-374. Ohms, S.R. 2003. Restoration of aspen in different stages of mortality in southern Utah. M.S. Thesis. Utah State University. Logan, Utah. 88 pp. Olson, K.C., R.D. Wiedmeier, J.E. Bowns, and R.L. Hurst, 1999. Livestock response to multispecies and deferred-rotation grazing on forested rangeland. J. Range Manage. 52:462-470. Parker, K.G., L.R. Mason, and J.F. Vallentine. 1979. Utah Grasses. Coop. Ext. Ser. Cir. 384. Utah State University, Logan. Pehanec, J.F. and G.D. Pickford. 1937. A weight estimate method for the determination of range or pasture production. J. American Soc. Agron. 29:894-905. Pieper, R.D. 1980. Impacts of grazing systems on livestock, p 133-151. In: K.C. Mc. Daniel and C. Allison (eds), Proc. Grazing Management Systems for Southwest Rangelands Symp. Range Improvement Task Force. New Mexico State University, Las Cruces, N.M. Ruyle, G.B. 1983. Sheep diets and feeding behavior in single and common use grazing trials on southwestern Utah summer range. P.h.D. dissertation. Utah State University, Logan. 111 pp. Ruyle, G.B. and J.E. Bowns. 1985. Forage use by cattle and sheep grazing separately and together on summer range in southwestern Utah. J. Range Manage. 38: 299-302.

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UAES Research Report 214 - Vegetation and Grazing on Utah Summer Range  

There is little doubt that excessive sheep grazing in the early part of the 20th century and continued sheep grazing to the present time has...

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