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Circular No. 925

Increasing Forage Yields
and
Sheep Production
on

Intermountain Winter Ranges

SELAR S. HUTCHINGS and GEORGE STEWART, Range Conservationists

Forest Service

UNITED STATES DEPARTMENT OF AGRICULTURE
WASHINGTON, D. C., September 1953

Czrcular No. 925

September 1953 * Washington, D. C.

UNITED STATES DEPARTMENT OF AGRICULTURE

Increasing Forage Yields and Sheep
Production on Intermountain
Winter Ranges

By SELAR 8. HuTcHInes, range conservationist, and GEORGE STEWART, formerly range
conservationist, Intermountain Forest and Range Experiment Station, Forest Service

CONTENTS
Page Page
iT brOdUCtION= ss SS 1 Black sagebrush subtypes__-_-____- 35
Methods*otstudiy2 22822 <2 co 4| Winterfat subtype containing Rus-
Winter range vegetation. ________-- 7 siah=thistle 7. ee i ee 39
Horage utilization =" 2 ee 12) Influence of grazing intensity on
Utilization of individual species__._ 12 sheep production_____________- 40
Periodic trends in utilization______ 14| Sheep production on range pastures 41
Influence of relative production of Sheep production on range allot-
Pherspe cies ar oh as ae 16 MMCNtSe see Oe ee 44
Influence of grazing intensity _ _ ___ 18 | Guides for increasing forage and sheep
Precipitation and its influence on production 2 (e722 As: 53
vegetatlOone 2: oars 19| Judging range condition_-_-_-_--__-___ 53
Precipitation records___-.______-- 1OJEe wWtihzation standards. 32229. o2 =. 54
Influence of precipitation on pro- Stockme rates. 2: soe es 55
CGNUIC GUO) ates Se Ss ae as ie ee 23 Management practices____-___-_-_- a7
Influence of grazing intensity on SUMIMATY ses Sis Sse eee 58
VER CUMIONe 88 ok eet Se. Zia atenatune. cited 2) es ae Ses 61
Shadscale and winterfat subtypes. 28|Common and botanical names of
Shadscale-Indian ricegrass subtype 33 species mentioned____________- 62
INTRODUCTION

The 65 million acres of winter range in the Intermountain region
supports only a sparse stand of vegetation, yet it furnishes forage for
approximately 4 to 5 million sheep each winter for a period of 4 to 6
months, from November to April. Since the early days of the sheep
industry in the West, the drier portions of the region have been used

2 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

for winter grazing. These semiarid ranges are well suited for such use
because the forage is composed of grasses and low shrubs that grow
during the spring and early summer, then dry and cure on the stem
before grazing begins. Light snowfalls, usually only 3 to 5 inches deep,
furnish water where permanent watering places are few and scattered.
This combination of well-cured herbage and easily available snow for
water generally provides favorable grazing conditions (fig. 1).

a i ; " — al

F—440852

FiGuRE |.—Sheep grazing winter range in western Utah. The soft snow, 2 to 3 inches
deep, and well-exposed plants provide ideal conditions for winter grazing. Vegeta-
tion is primarily winterfat and shadscale, with some bud sagebrush.

Winter ranges of the Intermountain region are located in eastern and
western Utah, Nevada, southwestern Wyoming, and southern Idaho
(fig. 2). Similar ranges extend into adjacent States. These ranges lie
in great blocks, often several million acres in size and usually at. con-
siderable distances from spring-fall and summer range lands.

In October most of the sheep within the region are trailed 50 to 200
miles from the spring-fall ranges to the winter ranges, returning over
the same trails in April and May (7).!. They are moved to the higher
mountains for summer grazing and are brought back to the spring-fall
ranges at the end of the summer period.

During the early development of the western livestock industry,
grazing on the vast areas of winter range was largely a matter of shifting
animals to new ranges. As those already in use became crowded, sheep
and cattle were moved into new areas more remote from centers of
civilization (1). More than 50 years ago, however, almost every part
of the West suitable for livestock was fully grazed and expansion into
new territory became impossible. Numbers of animals continued to
increase even after this and as a result, many winter ranges were seri-
ously overgrazed. Excessive use of the grazing resources brought about
reduction of vegetation and loss of soil through increased wind and

1 Italic numbers in parentheses refer to Literature Cited, p. 61.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 3

water erosion. Extremes in weather conditions and prolonged droughts
accentuated the seriousness of range depletion. Free use of winter
ranges in the Intermountain region ended when they were put under
management following passage of the Taylor Grazing Act of 1934.

Today the ‘‘frontier”’ of the livestock industry les in the application
of management practices which will restore and maintain ranges at their
maximum production of both forage and livestock. This is particularly
true of the winter ranges of the Intermountain region.

The Desert Experimental Range, a unit of the Intermountain Forest
and Range Experiment Station, maintained by the Forest Service, was
established in 1933 to study the major phases of winter-range manage-

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Figure 2.—Winter sheep ranges of the Intermountain region.

4 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

ment. Fifty-five thousand acres of representative winter range in the
salt-desert shrub areas of western Millard County, Utah, were selected
and fenced into allotments and experimental pastures. This circular
presents the results of studies extending over a 13-year period, 1935-47.
The chief objectives of the studies were to determine: (1) The utilization
of forage species by sheep; (2) the influence of precipitation on herbage
production and plant density; (3) the effects of grazing intensity on
forage yields; and (4) the effects of grazing intensity on sheep and wool
production. Results from these studies will be generally applicable to
the salt-desert shrub areas which comprise approximately 66 percent of
the winter ranges in the Intermountain region.

METHODS OF STUDY

For the purposes of the studies the Desert Experimental Range was
divided into range pastures and large range allotments (fig. 3). Most
of the herbage production and forage utilization data were obtained
from the experimental range pastures. Data obtained from the pastures
were supplemented with information on forage utilization from the
moderately grazed range allotments. An evaluation of the species which
make up the forage was obtained from the moderately grazed pastures,
by multiplying the average herbage yields of individual species by the
average percentage of its herbage that was eaten.

The effect of the precipitation on total herbage production was
determined by correlating the yearly precipitation, October 1 to Sep-
tember 30, obtained at the Desert Experimental Range headquarters
with the average herbage yields measured the following October on all
range pastures.

To evaluate the effects of grazing intensity on herbage yields data
were obtained from three sources—the experimental range pastures,
moderately and heavily grazed range allotments, and protected enclo-
sures. Herbage yields recorded each year on the lightly, moderately,
and heavily grazed range pastures were compared and yield trends were
computed for the total herbage as well as for individual species.

Most of the information on effects of grazing intensity on herbage
production was obtained from a series of 20 fenced range pastures (fig. 4).
Sixteen of these were 320 acres in area and four were 240 acres. Six of
the 20 pastures were grazed lightly, six moderately, and six heavily
during either one or a combination of two grazing periods of the winter
grazing season, as follows: Early, middle, late; early and middle; early
and late; and middle and late winter. These periods were arbitrarily
established by dividing the winter grazing season into three equal
periods of about 50 days. Early winter included the period November
15 to January 3; middle winter, January 4 to February 23; and late
winter, February 24 to April 10.

The other two pastures were grazed in the middle winter period, one
moderately and one at a heavy intensity similar to that on much of
the general winter range. This was somewhat heavier than the grazing
in the other heavily grazed pastures.

The desired intensity of grazing in each pasture was obtained by
varying the number of sheep grazed. The numbers grazed were ad-
justed each year to compensate for fluctuations in herbage yield. The
sheep placed in each pasture were weighed at the beginning of each

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 5)

LEGEND
m= EXPERIMENTAL RANGE BOUNDARY
—-—=— ALLOTMENT BOUNDARY
—--— UNIT BOUNDARY We
——— IMPROVED ROAD d
===== UNIMPROVED ROAD
— RESERVOIR
RAZ RIDGE

NO. 1

MIOWINTER

an =
~-s

‘i

* UNIT NO. 2

EARLY WINTER OR LATE
WINTER IN ALTERNATE YEARS
Y

UNIT/NO.2

Sa . 7
Besar ll

N) MIOWINTER OR LATE WINTER
( IN ALTERNATE YEARS

OVER FLOW / UNIT IN (

0.1
VARIABLE GRAZING Y EARLY WINTER EVERY OTHER \\

|)
Cw, cee
RANGE i y piece

PASTURES ee (—

MIDWINTER OR LATE WINTER
IN ALTERNATE YEARS

UNIT NO. 2

EARLY WINTER (t

Y UNIT NO|2 <->

MIDWINTER ak x

eee sees (e
ALLOTMENT NO. 4

| UNIT. NO./1 | UNIT] NO. 1
RLY WINTEROR MIDWINTER |

x
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(IN ALTERNATE YEARS | ( ) a) UNGRAZED i \. \
ae > i ) he EXERIMENTAL 0 SH
4 ‘ (y s RANGE SN Il
( )/ ( HEADQUARTERS |
4 Sy |

FicurE 3.—Location of range pastures and allotments at the Desert Experimental
Range. All allotments were grazed at moderate intensity.

grazing period and at the end of the winter grazing season. The grazing
intensities and the method of stocking the pastures are described in
more detail in the section, Influence of Grazing Intensity, page 18.
Data on herbage yields, plant density, and forage utilization were
recorded each year. Plant density and herbage production estimates
were made on a series of circular 200-square-foot plots established within
each pasture—64 in the large pastures and 48 in the small pastures.
Plant density, estimated by the square-foot-density method (20) in
October or early November, was recorded each year from 1935 to 1945
and in 1947. Herbage yields were determined by the weight-estimate

6 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

x XxX x x x

it
MIDDLE | EARLY ** EARLY * EARLY : i)
LATE | MIDDLE ,, MIDDLE , LATE | mipbLE | mippeE |! t
WINTER | WINTER || WINTER | WINTER | WINTER | WINTER
Sete ee se Oe ie oe See eee ee
MODERATE | MODERATE ’* LIGHT { LIGHT * MODERATES HEAVY ** }
k 4k ‘ ! k 1 !
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ee eS SS =
|| .
* MIDDLE ¥f i | EARLY 7
MIDDLE , LATE ji MIDDLE , EARLY { MIDDLE | LATE
WINTER WINTER || WINTER WINTER | WINTER WINTER

Hoe N08 Oe eee

‘MODERATE’ HEAVY * HEAVY 7% LIGHT

LIGHT | LIGHT

MIDWINTER

12 Uy 18
HEAVY

HE AVY
EARLY, LATE |

\ WINTER i LATE WINTER

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MODERATE | MODERATE

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MIDDLE LATE iE
WINTER EARLY WINTER *

14
HEAVY

EARLY, LATE
WINTER

EARLY WINTER
16

| 15
| MODERATE | HEAVY
bee ieee @ eee
Figure 4.—Fenced range pastures at the Desert Experimental Range. Intensities

of grazing in the pastures were light, moderate, or heavy during the various grazing
periods, as indicated.

method (12) for the same period with the exception of the first 3 years,
1935-37, for which they were determined from the density estimates,
using the calculated relation (regression) of density and yield for the
period 1938-47.

Estimates of herbage utilization were made at the end of grazing
periods on the same plots that were used for obtaining plant density
and herbage yield. Percentage utilization of individual shrubs and
grasses was determined by the ocular-by-plot method described by
Pechanec and Pickford (1/1). Percentage utilization of the current
herbage of each species was obtained by averaging the estimates made
on the plots. The weight of herbage utilized was computed by multi-
plying the total yield of each species by the average percentage utiliza-
tion.

Herbage yields obtained at varying periods on the moderately and
heavily grazed range and on the protected enclosures and heavily
grazed range were compared and used to supplement information
obtained in the experimental range pastures.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES a

To compare the effects of moderate and heavy grazing on sheep
and wool production two typical winter range allotments were selected
and grazed by full winter bands of 2,500 to 3,000 sheep.” In 1935
both allotments were similar with respect to topography, vegetation,
and range condition. One allotment was fenced, divided into units,
and moderately grazed. The other. allotment was heavily grazed.
The two herds selected were essentially similar with respect to breeding
history as well as summer and winter range operations. Sheep in
both herds were range-bred Rambouillets of good quality.

The two herds were alternated from year to year between the two
range allotments. This was done to eliminate as far as possible the
effects of any difference between the two herds.

Data obtained each year in wool yields, lamb crops, death losses,
sheep weights, and income were used to evaluate the effects of moderate
and heavy grazing intensity on sheep production. Management prac-
tices used for the two herds differed as well as intens'ty of grazing.
These are explained in detail in the section, Sheep Production on Range
Allotments, page 44.

WINTER RANGE VEGETATION

Vegetation used for winter grazing grows mainly on the broad semi-
arid valley lands, and on the low-lying hills and foothills within the
Intermountain region. The characteristic mixture of grasses and low
shrubs is sparse, and there are open spaces between the plants. As
estimated by the square-foot-density method, plant density varies
usually between 2 and 8 percent of the ground surface.

Four major plant formations are found on the winter ranges ae the
Intermountain region. The salt-desert shrub formation (fig. 5, A)
covers about 43 million acres, sagebrush-grass (fig. 5, B) 13 million
acres, pinyon-juniper woodland (fig. 5, C) about 8 million acres, and
the southern-desert shrub about 1 million acres. These plant forma-
tions are referred to as major range types in ‘‘The Western Range’”’
(21) and the Agriculture Yearbook for 1948 (14).

Vegetation on the Desert Experimental Range is representative of
the salt-desert shrub formation, which covers 66 percent of the entire
winter range. This formation includes a large number of plant associa-
tions or types which are usually composed of a mixture of shrubs and
grasses dominated by one or two species. These types are normally
quite distinct, but sometimes they merge imperceptibly into one an-
other (fig. 6). Many occupy large parts of a single valley and their
ageregate over the winter range may be several million acres. The
various types show preference for soil with certain characteristics with
regard to soil salts or to surface drainage, similar to those described in
Tooele, Escalante, Pine, and Wah Wah Valleys in Utah (9, 17, 19).

Shadscale is the most extensive plant on the general winter
range. It forms large almost pure stands on the deep, well-drained
soils in the valley bottoms. On the higher valley slopes and low hills,

2 Special appreciation is expressed to George C., Elray, Edwin, Alvin L., and
William D. Jackson, owners of the experimental herds, for their wholehearted co-
operation in the experimental grazing studies. Appreciation is also expressed to
John Bayless, Jess Guymon, Clarence Ingram, Walter James (deceased), Junius
Metcalf, and Harry Sperry; and to the Fountain Green Wool Growers and Fairview
Cooperative Sheepmen, who at various times participated in the experiments.

8 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

F—468713, 330794, 415770

Figure 5.—A, Typical shadscale-winterfat-grass subtype of the salt-desert shrub
formation; B, sagebrush-grass formation containing big sagebrush and galleta;

C, pinyon-juniper woodland formation with an understory of big sagebrush, win-
terfat, and Indian ricegrass.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 9

shadscale is mixed with grasses and other shrubs. Wherever grazing
has been excessive, on mixed shadscale-winterfat-grass ranges, the
palatable grasses and winterfat (‘‘whitesage”’) have often been sup-
planted by shadscale, which is protected from excessive grazing by
sharp thorns.

F-260665
Figure 6.—Small rabbitbrush type (left) merging into winterfat type (right). Plant
types are usually dominated by one or two plants, and lines of demarcation between
them are often distinct.

Two subtypes containing shadscale cover almost half of the Desert
Experimental Range. The shadscale-grass subtype occupies 14,276
acres and the shadscale-winterfat-grass is found on 12,687 acres (fig. 7).
When the grass within the subtype is primarily a single species, it is
listed in the subtype designation. For example, where Indian rice-
grass is a major species, the shadscale-grass subtype is often called the
shadscale-Indian ricegrass subtype. Shadscale in pure stands occupies
areas on the experimental range too small to map, although it is ex-
tensive on the general winter range.

The type dominated by winterfat is probably the second most ex-
tensive found on the winter range. Subtypes of almost pure winterfat
exist on the deep, fine, alluvial soils near the valley bottoms and in the
broad, fairly level drainages where runoff from summer storms ac-
cumulates. On the higher valley slopes, winterfat grows in mixture
with other species. These mixed subtypes furnish excellent forage for
sheep, especially if the associated species include Indian ricegrass or
black sagebrush. The winterfat type is represented on the experimental
range by two subtypes: Winterfat-small rabbitbrush-grass, 5,132 acres;
and pure winterfat, 3,949 acres.

Plant types dominated by mat and Gardner saltbushes are not widely
distributed within the Intermountain region; but on localized areas in
eastern Utah and southwestern Wyoming they are extensive enough to
be important. They are usually found in almost pure stands on the
lower valley slopes and level soils of the valley bottoms, which oc-
casionally receive runoff from melting snows or summer storms. Types
containing these saltbushes furnish excellent winter forage for sheep.

CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

LEGEND

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GRAY SUMMERCYPRESS-
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JUNIPER OVERSTORY

PASTURE AREA

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BARREN AND MISCELLANEOUS
MINOR SUBTYPES

4 MILES

SCALE

pes of the Desert Experimental Range as mapped and classi-

—Plant subty

FIGURE

fied in 1934.

tal Range in one

xperimen

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tely 3 million acres on the general
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INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 11

grows in almost pure stands on a few small sandy areas but for the most
part it occurs as a component in subtypes with winterfat, black sage-
brush, and shadscale. Other rabbitbrushes grow in sparse stands
along one or two of the larger drainage channels.

The sagebrush-grass formation covers approximately 13 million acres
or 20 percent of the winter range within the region. This plant forma-
tion consists largely of two plant associations or types, the big sage-
brush-grass, which occupies almost 10 million acres, and black sagebrush,
which covers about 3 million acres. The largest areas covered by the
big sagebrush type are found on deep alluvial soils along the foothills
and in the valleys of high elevation where annual precipitation is 10 to
15 inches, and the soil is well-drained and free from soil salts. On the
foothills the big sagebrush type often forms an understory with pinyon-
juniper, both often extending down the drainage channels into the black
sagebrush, winterfat, and shadscale types. It is also often found mixed
with shadscale or greasewood near the valley bottoms (9, 16, 17).
Most of the big sagebrush type is spring-fall range and only the low-
lying, more arid portions of the type are used for winter grazing.
While big sagebrush itself is only moderately palatable under normal
winter conditions, it is often heavily grazed during periods of deep
snow. The associated species in the big sagebrush type on winter
range furnish considerable forage, especially when they include desir-
able and palatable species like galleta, winterfat, or squirreltail.
Although the big sagebrush type covers large areas on the winter range
in the Intermountain region, it occurs only as scattered plants along
one or two of the drainages within the experimental area.

The black sagebrush type is one of the most productive and desirable
on the winter range. ‘This type grows on the rocky soils of the higher
valley lands and foothills where soil is well-drained and soil salts are
not excessive. Soils are usually much shallower than those where big
sagebrush grows because a caliche layer (crust of calcium carbonate)
is commonly formed 18 to 24 inches below the surface. Intermingled
species include Indian ricegrass, Salina wildrye, needle-and-thread,
galleta, bud sagebrush, and small rabbitbrush. Pinyon-juniper and
littleleaf mountain-mahogany sometimes form an overstory, either in
patches or open stands.

The black sagebrush type provides choice grazing for sheep. Besides
being productive, black sagebrush and most of the associated species
are highly palatable. Only two black sagebrush subtypes are found
on the experimental range. One, the black sagebrush-shadscale-grass
subtype, which covers 8,981 acres, is probably one of the most produc-
tive on the experimental range. In the other, black sagebrush and
grass occur as an understory within the scattered littleleaf mountain-
mahogany on 4,542 acres. In addition to these two subtypes, black
sagebrush is found on some areas mixed with winterfat and small
rabbitbrush.

The pinyon-juniper woodland formation extends over about 8 million
acres (12 percent) of the winter range. Most of the pinyon-juniper
grows in open stands, usually with big sagebrush and black sagebrush
in the understory. Dense stands of pinyon-juniper with little herba-
eeous or shrubby understory are found on considerable areas of the
winter range. On the experimental range Utah juniper and singleleaf
pinyon form an open, scattered overstory on 10,560 acres. The range

12 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

covered with pinyon and juniper has been classified on the basis of the
vegetation found growing in the understory.

Some vegetation of the southern-desert shrub formation, charac-
terized by shrubs of low grazing value such as creosotebush, yucca, and
mesquite, occurs in southwestern Utah and southern Nevada (24)
Only about 1 million acres of this area is used for winter grazing because
of scanty rainfall and consequent low, undependable forage production.
This plant formation does not occur on the experimental range.

At least four introduced annuals—Russian-thistle, cheatgrass and
foxtail bromes, and halogeton—have invaded large areas of the winter
range. Although these plants are not considered in this circular as
forming subtypes, they have considerable effect on grazing, since they
have supplanted the better native forage species on many winter ranges.
They therefore need careful consideration in any program designed to
improve winter ranges.

Russian-thistle, the oldest of these invaders, grows profusely in
depleted winterfat and big sagebrush subtypes whenever summer pre-
cipitation is ample. Cheatgrass and foxtail bromes have taken over
large parts of depleted shadscale and black sagebrush subtypes, in some
places making up more than half the vegetation. It is also prevalent
in the big sagebrush types where other grasses have been destroyed.
Halogeton, the most recent intruder, has spread over much winter
range land in Nevada, Idaho, and Utah, being well adapted to saline
soils. It grows mainly on overgrazed and depleted ranges, and along
road shoulders or on other land that has been disturbed, such as aban-
doned dry-farms or trampled areas. If eaten in quantity, this plant
is poisonous to sheep. Two of these species, Russian-thistle and
cheatgrass brome, occur on the experimental range in minor quantities

FORAGE UTILIZATION

Although several hundred plant species are found on the winter
range, only 30 are abundant and palatable enough to be classed as
important for forage. The importance of a plant as forage is deter-
mined largely by two factors—its relative abundance and the degree
to which it is utilized. These two factors are not independent of each
other, and must be considered together in assessing the importance of
the different species.

Most of the grazing on winter ranges, especially during the early
midwinter period, occurs while the plants are dormant. The grasses
are cured and dry except for a few basal leaves and stems which often
remain alive and green during part of the winter. Most of the shrubs
are completely dormant, although the twigs and stems on a few species
appear to remain alive and somewhat succulent in most years. The
forage therefore consists largely of mature, dry herbage. In the late
winter period, in years w hen plant growth starts early, “the sheep relish
the new green vegetation, especially that of bud sagebrush and grasses.

UTILIZATION OF INDIVIDUAL SPECIES

Ratings of relative abundance within the naturally sparse stands of
vegetation on winter ranges, and utilization data obtained on all mod-

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 13

erately grazed areas at the Desert Experimental Range, including both
range allotments and pastures, serve to illustrate how these factors
are related in determining the importance of various species as forage
(table 1).

Only a few of the plants whose herbage is utilized at 45 percent or
more are relatively abundant and occur widely over the winter range.
These include winterfat, Indian ricegrass, galleta, and globemallow.
Other species such as hopsage, black sagebrush, bud sagebrush, four-
wing saltbush, squirreltail, sacaton, Salina wildrye, and Mormon
needlegrass, whose herbage is utilized 45 percent or more, generally
occur in limited subtypes or comprise only moderate or minor amounts
of vegetation. With the exception of shadscale, species utilized below
this level occur in only one or two localized plant subtypes or form only

TaBLE |.—Relative abundance and average utilization of herbage by sheep
of principal forage plants on moderately grazed pastures and allotments
at the Desert Experimental Range, 1936-46

Average
Species ae , | utilization of
herbage
Shrubs: | Percent
PO PSAGe ep llVe es ee Te Mee en ee 1 | 80
Sagebrush. blacks. 28320502 8 er Pi ee 2 70
Wantertat. common 2-128: ise a 60
Sagebrush. buds iss <2 5 ey eee Ne on 50
Saltlushs (ourwine- aes oe 1 50
Savebrushs pingeds22 272i en Ae eee ie ila 40
SumuImer-cy press evay = sso ee 1 | 35
Saltbush Gardner. 222 o55 2 ee i 1 | 30
Saltbush, shadscales<. 2.0 so 2 ie ESE i 25
Mountain-mahogany, littleleaf__.________________ 1 | 25
Bphedra, Nevada te 8 ao Ue Oia at ea 2 20
Snakewecd «broom eae ee a ee 2 15
Rabbit brushtismalies: a2. sek he ei eee 3 10
Rabbitbrushe Tu blberes ss Scat S ee he LT 10
Grasses: |
Squirreltail, bottlebrush=«=" 202 75 tei. is Sa 75
Sacatone alkaline et cee oe ee 3 | 75
Riceerass indian eee a ae 4 | 75
WWildiviewSalinai ce se we. ae ah 2 | 45
Galle tas ey ee Se ee Ge 5 45
Needlegrass,. Wormons se ea eS 1 45
Wheatgrass, bearded bluebunch__________________ 2 30
Dropseed=: Sands shy 5 ee Oe te 3] 25
Dropseed spike’. 272 see ee 1 | 20
Grama les rs ee ee ea | 20
Forbs:
Globemallow,, cooseberryleat. 2 ="= 23. 2 4 80
REPDERWECU oe er ee Fa hae re Oe aie ZA 25
Russian-thistle tumbling: <2 282255 3 10

_’ Based on a scale from 1 to 5: 1, occurring infrequently in minor subtypes; 2, well-
distributed in minor subtypes or infrequent in major subtypes; 3, present in moderate
numbers in major subtypes; 4, well-distributed in one or more major subtypes -
5, dominating one or more major subtypes.

14 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

a small part of the plant cover. Many other plant species in addition
to those listed furnish some forage, but the contribution of each is
extremely small except in a few areas.

Blue grama, a desirable and highly palatable forage species in the
Southwest and Plains regions, is utilized only very lightly on the Inter-
mountain winter sheep ranges. Average use of the herbage of this
species was only 20 percent.

Bearded bluebunch wheatgrass, considered to be one of the major
forage species on the spring-tfall ranges of Utah and Idaho, is found on
only a few of the foothill areas of the winter ranges, and is utilized only
about 30 percent.

Bottlebrush squirreltail, a species generally considered to have low
palatability on spring-fall and summer ranges, is one of the most palat-
able of all winter forage species. The basal leaves of this plant begin
to grow in the late fall and they remain green and succulent during
the winter. Sheep relish this green foliage. Only scattered plants of
squirreltail occur on the heavily grazed winter ranges. However, under
moderate grazing or protection, this species increases in abundance on
the foothill areas.

More exact information on the relative importance of several plants
as forage was obtained within the seven moderately grazed range
pastures during the period 1935-45 (table 2). Of the forage used
_ during this period, shrubs made up 59 percent, grasses 36 per cent, and
forbs 5 percent. Seven species contributed almost 95 percent of the
total forage. Five of these—winterfat, shadscale, Indian ricegrass,
galleta, and sand dropseed—produced 80 percent of the herbage and
furnished 88 percent of the forage.

Differences between the proportion of total herbage produced and
that utilized as forage are due primarily to differences in palatability,
although several other factors such as growth habits of plants also
influence the degree of utilization. As table 2 shows, the more palat-
able species—winterfat, Indian ricegrass, galleta, bud sagebrush, and
globemallow—contributed a higher proportion of the forage than of the
total herbage. The species of lower palatability—shadscale and sand
dropseed—provided a lower proportion of forage than of herbage.

PERIODIC TRENDS IN UTILIZATION

When sheep first begin to graze a winter range they select primarily
the choicest portions of the more palatable forage species such as the
seed stalks of black sagebrush and Indian ricegrass. At later intervals
as the choicer forage is consumed, more of the moderately palatable
forage is eaten. Toward the end of a winter grazing period, sheep
subsist mainly on the less palatable species.

This pattern of utilization is typical of both the early and midwinter
grazing periods when the vegetation is cured and dry, and little if any
new erowth is available to the sheep. Table 3 shows the percentage
utilization of several forage plants during a 40-day midwinter period on
a typical moderately grazed range allotment. During the first 10 days,
sheep ate 45 percent of the globemallow, 40 percent of the black sage-
brush, and 35 percent of the Indian ricegrass herbage, and only small
amounts of bud sagebrush, winterfat, galleta, and shadscale. During
the second 10-day interv al, rather heavy use of globemallow, black
sagebrush, and Indian ricegrass continued, but during the third interval

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 15

grazing of these highly palatable species dropped sharply because little
of the choice herbage remained to be eaten. At this time, utilization of
bud sagebrush increased noticeably and that of winterfat and shadscale
slightly. In the fourth interval, grazing of the highly palatable species
continued low, that of bud sagebrush dropped, and consumption of
winterfat, galleta, and sand dropseed increased. At the end of the
40-day period the study area was considered to be about properly grazed
although the globemallow and black sagebrush probably received more
than a desirable degree of use. :

TABLE 2.—Average herbage production, percent utilization of herbage by
sheep, and forage furnished on seven moderately grazed range pastures
at the Desert Experimental Range, 1935-45

Herbage production Forage furnished
iene sssiseet Herbage |__ Se
Species utiliza-
Quantity | Grtotal | | Quantity | SP total
Shrubs: Lb. /acre Percent Percent Lb./acre Percent
Wintertat 32s: ACT: 22.4 54.0 25.8 Byoaa
Bud sagebrush______ 3.4 1.6 52.1 deez Ze
Shadscale____-__2_- 60.6 28 .4 2135 12.9 17.6
@ther «252 suas ee 23410. eel 12.2 2.9 3.9
Alleshrubss 2-35) 135.4 63.5 32.0 43.3 58.
Grasses: | |
Indian ricegrass_____) 14.2 6.7 73.3 10.4 14.1
Galletac2s ees 20.0 9.4 46.9 9.4 12.8
Sand dropseed_____- Deeks 13.0 22.8 6.3 8.6
Otheresas ie ees 4.8 2.2 6.8 Leo A
All grasses_______| 66.7 31.3 39.6 26.4 35.9
Forbs: |
Globemallow _ -_ ____- 4.3 2.0 74.1 one 4.4
Pherae eee 6.8 Die 9.2 6 8
ANT forbs == Lid be 343 3.8) 5.2
Totals, Pisa) 100 | 84-4 73.5 100

In years when precipitation was favorable and winterfat made rank
woody growth and produced good seed crops, utilization was lower
than in years when it did not fully mature. In each of the winters
1935-36, 1937-38, and 1938-39, when winterfat had made excellent
growth, utilization of its herbage and tender twigs was only about 45
percent. The average utilization was about 65 percent in years when
it did not mature.

Repeated observations on the moderately grazed ranges revealed
that the shorter growth of winterfat, on the gravelly soils of the foothills
and valley slopes was utilized more heavily than the more thrifty,
coarser growth found on the finer soils in the drainages and valley
bottoms.

16 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 3.—Percentage utilization of total herbage production of forage
plants on a moderately grazed range allotment during 10-day intervals
in a 40-day grazing period of a rather typical winter

Species Jan. 5-14 | Jan. 15-24 eee Feb. 4-13 Total

Frequently sheep ate only the central portions of galleta tufts, leaving
the coarser growth around the edges. They also ate some individual
patches but left adjacent ones untouched.

Sheep definitely preferred the tops of Indian ricegrass and the seed-
stalks and foliage of small plants to the herbage produced by large
plants. Utilization of this species was also heavier in years when late
summer rains stimulated the growth of the basal leaves and freshened
up the herbage.

During short periods throughout the winter when melting snow
softened the otherwise dry vegetation, sheep often ate galleta, sand
dropseed, blue grama, and Russian-thistle in preference to other nor-
mally more palatable species.

In some years many forage species such as spiny hopsage, bud sage-
brush, squirreltail, Indian ricegrass, and Salina wildrye began to grow
in March and April, during the late winter grazing period. Sheep
relished this green succulent growth and ate it in preference to herbage
of other species which was still dry and dormant, thus altering the
utilization pattern during this period.

INFLUENCE OF RELATIVE PRODUCTION OF THE SPECIES

In general the percentage utilization of the herbage varied with the
amount and relative production of the different species. The grazing
of a given species tended to increase with a decrease in its relative
production (table 4).

Data from moderately grazed range pastures show this inverse rela-
tion. In pasture 6, where winterfat production averaged 4 pounds per
acre and made up only 2 percent of the total herbage, 77 percent of the
herbage was utilized. In pasture 16 with 118 pounds of winterfat
herbage, 51 percent of the total yield, average utilization was only 48
percent.

Utilization of several other species also followed the same general
pattern. Grazing of Indian ricegrass, galleta, and sand dropseed was
greater on range pastures where yields were small and less on those
where yields were high. This relation was less pronounced for galleta,
which was fairly evenly distributed on the range.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES’ 17

The weighted utilization of the three grasses taken together was also
affected by the relative amount of total grass herbage available. In
fact, the inverse relation of utilization to production was closer than
that for any of the individual grass species.

TABLE 4.—Average herbage yield, proportion of total, and herbage utiliza-
tion of four major forage species in moderately grazed range pastures,
1938-46

Species and Herbage Proportion of Herbage
pasture number yield total yield utilization
Winterfat: Pounds per acre Percent Percent
Sie eee ee ee 4 2 (7
Oe en nce erie 6 3 59
Qasr et ses 15 8 58
eee eg ONS ee ees 28 15 62
OX gee ara eS ee ae 90 45 49
QE Cee 109 51 54
Gi ee 118 51 48
Indian ricegrass
0 Fe SO aaa eee ew 5 3 73
Qe esc ee 6 3 92
EGE Pee ee ee a Nes 7 3 91
7) Se OSES Se pls Ba 8 4 82
Dee rg SER Fires a 9 5 77
Dee ec ese meee ney Ga 19 10 60
Gree Ps ie ee 21 11 66
Galleta:
(Gea e Raa ees 9 8 29
DO'S eae eI ES 12 6 73
7d es cepts eRe aia 14 7 58
QE ie se 15 7 65
Oe ee ae St when SS ae 25 13 32
Oe Fe i Soe ee EONS ieee 25 14 39
DOR na oR ee 26 14 o4
Sand dropseed:
JI GPS es eacrnecne a ee a (#) (?) 48
[Os Sele a a 1 (2) 57
7d 0 ee RTs tee Dee a 6 4 28
(DRESS ST oe ieee Se 24 12 9
yen are pera cca te ea Ne ae 31 16 8
De AS 37 21 20
1S BU es ere ona ae 56 30 IL

' Less than 1 pound per acre.
2 Less than 1 percent.

The degree of use of a grass species is affected by the relative avail-
ability of herbage of other grasses. Sheep strive to include a certain
amount of grass in their diet. If they cannot obtain it from the choice
Indian ricegrass, they eat more galleta and sand dropseed. Utilization
of galleta and sand dropseed was low in pastures 5 and 6, where Indian
ricegrass yields were the greatest. In pastures 16, 19, and 20, where
all three grasses were most heavily grazed, yields of Indian ricegrass
and the other two grasses were relatively low.

18 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

Utilization under heavy and light intensities shows the same general
relation to herbage yields as that under moderate grazing. For ex-
ample, under heavy grazing utilization of winterfat was 80 percent in
pastures where it comprised only 10 percent of the total herbage and
58 to 64 percent in areas where it made up 25 to 30 percent of the total —
herbage. Under light grazing about the same relation existed between
utilization and herbage yields, although the spread in utilization per-
centage was not as pronounced as under moderate and heavy grazing.

The utilization of highly palatable species, on ranges where they made
up only a relatively small part of the total herbage, was often excessive
before sheep would eat much of the herbage produced by less desirable
plants. Because of the wide variations in utilization associated with
the relative herbage production of the palatable forage species, it is
necessary to govern the stocking rate not only on the presence of these
species, but also on the relative yields of the species within the plant
cover. On depleted ranges where desirable forage species constitute
an extremely small proportion of the herbage, stocking rates must
necessarily be low enough to permit these scarce species to increase.

INFLUENCE OF GRAZING INTENSITY

On the experimental range pastures three degrees of grazing—light,
moderate, and heavy—were applied. The plan was to maintain fairly
uniform utilization of the herbage produced the previous summer by
three key forage species. Planned utilization by weight under mod-
erate grazing was 75 percent for Indian ricegrass and 50 percent for
winterfat and bud sagebrush.

The desired intensity of grazing for the various range pastures waS
obtained and controlled reasonably well by varying the stocking each
year on the basis of October herbage estimates. The moderately
grazed pastures were stocked at an average rate of approximately 14
sheep-days per acre. Pastures designated as heavily grazed had about
25 percent heavier stocking (17 sheep-days per acre) and those lightly
grazed 30 percent lighter (10 sheep-days per acre) than those grazed at
moderate intensity.

The average yearly percentages of utilization of the herbage of the
major forage species, obtained under the three intensities of grazing
for the period 1935-46, are given in table 5. Utilization of the various
species under light and heavy grazing was not uniformly 25 percent
higher or 30 percent lower than that obtained under moderate grazing
as might have been assumed would be the case under the plan of
stocking. Utilization of winterfat under moderate grazing, for ex-
ample, was only slightly above that under light grazing. However,
in heavily stocked pastures sheep ate 11 percent more of the winterfat
herbage than in moderately stocked pastures. This represented ap-
proximately 20 percent greater use. There was a similar spread in
the utilization of Indian ricegrass between the three intensities of
grazing. With light stocking sheep ate only small amounts of galleta
and sand dropseed, 25 and 9 percent of the herbage, respectively. As
the grazing intensity increased they consumed more and more of these
species. Under heavy grazing, utilization of galleta herbage was 67
percent and sand dropseed 40 percent.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES. 19

The utilization of the three grasses under the three intensities of
grazing was interrelated. In lightly stocked pastures the sheep utilized
65 percent of the choice Indian ricegrass and only 25 and 9 percent of
galleta and sand dropseed, respectively. With moderate stocking the
sheep ate more of the desirable portions of Indian ricegrass and also
considerable quantities of galleta and sand dropseed. In _ heavily
stocked pastures sheep used all the edible parts of the Indian ricegrass
and were forced to eat much more of the galleta and sand dropseed
herbage in addition.

Under heavy grazing, the desirable forage species were closely grazed
and often seriously injured or killed. Asa _ result subsequent yields
were often impaired. Sheep were then forced to eat large amounts
of herbage from the less desirable species.

Shadseale, which is protected by thorns or spines, was utilized about
equally under light and moderate grazing and only slightly more under
heavy grazing.

The average utilization by sheep of winterfat, bud sagebrush, and
Indian ricegrass, the three key species, under moderate grazing was
fairly close to the predetermined plan. The average percentages of
utilization obtained for winterfat, bud sagebrush, and Indian ricegrass
were 55, 52, and 76 percent, respectively. Wide variations occurred
from year to year, however, and utilization of the individual species
varied independently. For example, the lowest utilization obtained
under moderate grazing for winterfat was in 1937-38, while the lowest
utilization of bud sagebrush occurred in 1943-44 when utilization of
both Indian ricegrass and winterfat was relatively high. In 1945-46
when utilization of winterfat was just below average, that of both bud
sagebrush and Indian ricegrass reached a maximum.

Because wide fluctuations in utilization occur from year to year,
utilization standards established as grazing guides should provide for
allowances to compensate for variations in vegetation and production.

PRECIPIEATION AND EIS INFLUENCE
ON VEGETATION

Range plant growth and herbage production are markedly influenced
by both annual and seasonal fluctuations in precipitation. Low and
extremely variable precipitation is typical of the winter ranges through-
out the Intermountain region. Annual precipitation on winter ranges
is usually less than 10 inches a year. At the Desert Experimental
Range mean annual precipitation (January to December) was 6.64
inches for the period 1934—47. This low annual precipitation is the
chief factor limiting plant growth and consequently herbage production.

PRECIPITATION RECORDS

Precipitation records at the Desert Experimental Range began in
1934. For comparison with records of longer duration, data for the
experimental range and for weather stations at Modena and Deseret,
Utah, are charted in figure 8. These two stations are located relatively
near the experimental range, one 55 miles south, and the other 75 miles
northeast.

CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

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INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 21

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22, CIRCULAR 925, U. 8S. DEPARTMENT OF AGRICULTURE

Mean precipitation at Modena for the period of record (1901-47)
was 10.83 inches; at Deseret (1900-47) it was 7.84 inches. Means at
both places—10.85 and 7.10 inches, respectively—for the period of
study, 1934-47, compare rather closely with these figures. It is there-
fore reasonable to believe that mean precipitation at the Desert Experi-
mental Range during the period of study is fairly representative of what
might be expected over a longer period of time. Fluctuations in yearly
amounts at all three locations followed a similar pattern, with few
exceptions, during the period 1934-47. Fluctuations at Modena and
Deseret were also similar in pattern during the longer period of record.

Rainfall data at the experimental range headquarters have been
tabulated by 3-month periods for a 12-month rainfall year, from
October 1 to September 30, because plant growth on the winter range
begins about March or April and almost all growth is completed before
the end of September (table 6). Precipitation for October to December
is considered as contributing to the next year’s growth. On this basis
mean annual precipitation at the Desert Experimental Range was 6.69
inches for the period of the study, with a minimum of 3.78 inches in
1941-42 and a maximum of 11.10 inches in 1946-47. Precipitation
was above average in only 5 of the 13 years.

TABLE 6.—Seasonal and yearly precipitation (inches) at Desert
Experimental Range headquarters, October 1 to September 30, 1934-47

Period | Oct.—Dec. | Jan._March | Apr—June | July-Sept. Total
034-952 | 0.59 0.87 2.42 4.00 7.88
1935 36-0 | i 1.62 21 4.20 6.34
1986-37. 1.64 | 87 1.05 | 2.28 5.84
087-3855 =| 1.08 1.52 3.41 | 2.81. 8.82
493823002 = | 2.05 86 2 AZ | 1.28 6.66
1939-40. = 2 = | 98 1.49 53 1.62 4.62
7040-41-65 = | 1.18 1.51 | 3.29 1.74 7.72
‘Cue as 2.15 32 | 50 81 3.78
1049-43 97 1.02 1.27 1.12 4.38
gua 44 | 2.62 | 86 2.45 26 6.19
(OM=45 2 e | 1.14 | 1.49 2.15 | 3.75 8.53
1945-46... ____| 1.06 | 29 1.47 | 2.35 5.17
1046-47 | 6.74 | 08 | 2.78 | 1.50 11.10

fee 1.73 98 | 1.85 2.13 6.69

Seasonal precipitation fluctuated widely. In general, its pattern and
seasonal distribution showed little consistency. Less than one-fourth
inch of precipitation occurred in many individual months, and less than
one-half inch in several of the 3-month periods. Precipitation for the
October to December period varied from 0.31 inch to 6.74 inches.
Precipitation for the January—March period averaged only 0.98 inch.
This was consistently a dry period.

Precipitation for the two growing periods, April to June and July to
September, was relatively high, averaging about 2.00 inches for each
period. During the latter period rainfall was cyclic in character. It
was relatively high during the first 4 years, low from 1939 to 1944, and
relatively high again in the next 2 years.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 23

Much of the winter precipitation comes as snow. This seldom
exceeds 4 or 5 inches in depth except in the foothills and desert moun-
tains. Often the storms are erratic and poorly distributed. Since
sheep depend largely on snow for water, ranges are often used unevenly.
In severe winters or during heavy winter storms the snow often becomes
too deep or too firmly crusted to permit effective grazing. If deep
snow persists over large areas, the sheep become extremely poor and
often die because they are unable to obtain sufficient forage. In the
last 20 years such conditions have occurred several times, notably in
the winters of 1931-32, 1936-87, 1948-49, and 1951-52.

When strong winds accompany a snowstorm or follow immediately
afterwards, deep snowdrifts are formed. These hamper the movement
of sheep and limit grazing to ridges blown free of snow.

According to rain-gage records, summer storms are also localized and
often occur as torrential downpours of high intensity. For example,
on May 2, 1935, 1.20 inches of precipitation fell in less than 20 minutes
in the south end of Wah Wah Valley. Areas a short distance away
received no rain. On July 28, 1936, Antelope Valley received 1.57
inches of rain in 23 minutes, but there was none at the Desert Experi-
mental Range headquarters 6 miles to the east. During such torrential
storms much of the precipitation is lost in runoff and consequently is
not available for plant growth.

INFLUENCE OF PRECIPITATION ON PRODUCTION

Forage plants on the winter range consist of a mixture of early- and
late-growing species. Many of them, including the shrubs and such
grasses as Indian ricegrass, squirreltail, and bearded bluebunch wheat-
grass, begin to grow in the latter part of March or in early April,
provided soil, moisture, and weather conditions are favorable. Some
of these species continue to grow throughout the summer if rainfall is
adequately distributed. In dry summers plant growth stops, the
herbage becomes dry and brittle, and frequently the plants fail to
produce flowers or seed. Some forage plants, primarily such annual
forbs as Russian-thistle and such grasses as galleta, sand dropseed, and
blue grama, begin to grow in May and June. ‘These species generally
depend on summer precipitation to make their growth. Almost all
plant growth on the winter range is completed by September, though
late rains often freshen and soften the herbage.

TOTAL HERBAGE YIELD

The total air-dry herbage yield was estimated annually on each range
pasture. These data were averaged and used to determine the relation
between production and precipitation. In most years herbage produc-
tion was estimated directly. However, yields for the first 3 years were
calculated from plant density; and the production for 1946, when no
data were taken, was calculated from the relation of production to
precipitation.

Air-dry herbage yield on all pastures for the period 1935—47 averaged
219 pounds per acre. The maximum yield of 468 pounds per acre was
recorded in October 1947, immediately following the 12-month period

24 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

of highest precipitation. This was more than six times the minimum
yield of 75 pounds per acre, which occurred in October 1943 following
two consecutive years with below-average precipitation.

The total herbage yield on the winter range as measured in October
was found to be closely related to the precipitation during the preceding
12 months. This relation of ker bage yield to precipitation is shown in
figure 9. Within the limits of variaticn in precipitation observed at the
Desert Experimental Range, berbage production increased about 46
pounds per acre (dry weight) with each additional inch of precipitation.

(POUNDS PER ACRE)

PRECIPITATION
Ve
/

PRECIPITATION (CINCHES)

PRODUCTION

HERBAGE PRODUCTION

AVERAGE PRODUCTION
AND
PRECIPITATION

6)
1935 1937 1939 194] 1943 1945 1947

FIGURE 9.—Average annual air-dry herbage production as measured in October in
all range pastures at the Desert Experimental Range and precipitation during the
preceding 12 months, 1935-47.

The close relation between precipitation and herbage production
provides a basis for estimating October herbage yields from the amount
of precipitation received each year® (fig. 10). Reliable estimates of
herbage yield for years when rainfall is between 4 and 11 inches can
be made directly from the chart. Herbage production increases with
precipitation as indicated by the slope of the estimating line. The
relation between the measured herbage production and precipitation
for individual years is shown by the dots.

3’ Equation for estimating herbage yield from previous 12-month precipitation
(calculated from data for 1938-45 and 1947) is:

Ye = — 92.46 + 45.802 with a standard error of estimate of + 41.25

where Ye is the expected air-dry herbage yield in pounds per acre and r is the 12-
month precipitation in inches. Correlation betw een Hurheee production and pre-
cipitation for this period of measurement was r = + 0.9

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 25

HERBAGE PRODUCTION (POUNDS PER ACRE)

STANDARD

ERROR OF Se
4

PRECIPITATION (INCHES)

Fiaure 10.—Relation of October herbage production to precipitation during the pre-
- ceding 12 months at the Desert Experimental Range. This chart can be used to
estimate herbage production from the precipitation in other years. |

To use the chart a vertical line is projected upward from the amount
of precipitation until it intersects the estimating line. A horizontal
line is then projected across to the left-hand margin where an estimate
of herbage production can be read. Asan example, the average herbage
production expected for a year with rainfall of 8 inches would be ap-
proximately 275 pounds per acre, as read from the chart. The actual
production obtained may be higher or lower than the estimated amount,
depending on seasonal distribution and character of the precipitation
and whether or not precipitation was above or below average the pre-
ceding year. However, in about two-thirds of the years, the actual
herbage yields obtained would not be expected to vary more than 41 to
50 pounds above or below the estimated amounts. ‘These limits are
indicated by the dashed lines in figure 10.

This method of prediction has been useful in providing an estimate
of herbage production, without the time-consuming necessity of sam-
pling the vegetation, before sheep reach the winter ranges. Herd owners
have thus been enabled to purchase supplemental feeds or otherwise
provide for anticipated short forage. Although the data apply par-
ticularly to the range area at the Desert Experimental Range, they can
also be applied to other winter range areas where the vegetation, con-
dition of the range, and amounts of rainfall are similar. Where these
conditions are not similar, relationships could be developed for specific
areas from herbage weight determinations made over a period of years.

26 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

Seasonal distribution of precipitation also influences herbage yields.
Most of the fall and winter precipitation filters into the soil, where it is
retained and used by forage plants to make early spring growth. In
contrast, much of the summer precipitation, which comes as localized
torrential storms, is lost as surface runoff. Also, during the summer
months losses by evaporation are large because temperatures are high
and desiccating winds are common. Analysis of data from the pastures
where the vegetation is chiefly shadscale, winterfat, galleta, and drop-
seed indicates that precipitation between October and December was
about twice as effective in the production of total herbage as that
between April and September, and that precipitation during the other
three months, January to March, was about one and one-half times as
effective.

YIELD OF INDIVIDUAL SPECIES

Individual species respond differently to precipitation. Yield of
shadseale and winterfat in October, like total herbage, was found to
be closely associated with precipitation during the preceding 12 months
(fig. 11). These two species produced more than half of the total
herbage in the experimental pastures and therefore largely influenced
total production. Production of these two shrubs fluctuated widely
from year to year. Yields of shadscale followed changes in precipita-
tion more closely than did winterfat or any other species.

200 )
{3
=
y
s (2
160
: rue
k
: | 2
= SHADSCALE pee 3
2 120 Aa So
SS ! 9 =
A PRECIPITATION !
= i We a A 3
9 / \ /\ ! 8 nN
c ‘ ie Lex I x
G BOK = ’ 5 Sa ~
S ‘ \ i) \ ! Q
S ‘\ ‘ ‘ 1A\ if \ : :
/ ’
x he: \. p \ Ih \ '/ &
- Sey oe \ if \ f 6
ie)
S si : BS \ ae 1 6
& oes ee LW " 5
/
iy we AS
x WINTERFAT —=-
wey
O
1935 1937 1939 194] 1943 1945 1947

FicuRE 11.—Average herbage production in October of the major shrubs, winteriat
and shadscale, in the 20 experimental pastures in relation to rainfall during the
preceding 12 months, 1935-47.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 27

Mortality of shadscale was relatively high during the drought period
1942-43, when it was estimated that 20 to 30 percent of the shadscale
plants died. During this same period very little loss occurred in other
forage species. Although production of shadscale and winterfat each
declined to 18 pounds per acre in 1943 following 2 years of drought
accompanied by heavy mortality of shadscale, they responded quickly
to favorable precipitation the following years. In 1944 with just below
average precipitation, 2.62 inches of which came in the October—
December period and 2.45 inches in the April—June period, the dormant
winterfat plants quickly revived and many shadscale seedlings appeared.
In that year shadscale and winterfat produced 93 and 69 pounds per
acre, respectively. By October of 1947, following 4 years of average
or above-average precipitation, yields of these two shrubs reached a
maximum. Winterfat produced about 90 pounds per acre and shad-
scale 195 pounds, more than twice their average yield. This demon-
strates the remarkable ability of the winter range vegetation to recover
from the effects of drought.

The three major grasses—Indian ricegrass, galleta, and sand drop-
seed—showed differing responses to variations in precipitation, but in
general their yields were closely correlated with previous 15-month
precipitation (fig. 12) rather than with the previous 12-month pre-
cipitation. Analysis of data for the period 1938-45 and for 1947
showed that sand dropseed followed variations in 15-month precipitation
most closely. In 1936, yield of this species as calculated from plant
density was unusually high (59 pounds per acre). Most of the increase
was due to the numerous seedlings produced in 1935 and 1936 as a
result of favorable late spring and summer rains. Many of these
seedlings failed to survive through 1937. .

Yields of galleta followed variations in 15-month precipitation closely
but somewhat less so than those of sand dropseed. Relatively high
yields of both these grasses occurred in 1938, 1939, 1941, and 1947, all
years with high spring and summer rainfall.

Production of Indian ricegrass showed the lowest correlation with
15-month precipitation. In 1938, with prior 15-month rainfall of 11.10
inches, yield of Indian ricegrass was 17 pounds per acre; in 1939, with
2 inches less rainfall, yield was the same; and in 1945, with 8.79 inches,
yield was only 9 pounds.

Yields of all three grasses fluctuated with precipitation but showed
a general decline from 1935 to 1942-43, during a period generally char-
acterized by below-average rainfall. The lowest yields of all grass
species occurred in 1943 following the 2 years of drought. After the
drought period production increased rather rapidly until 1947 when
yields were highest. Although grass yields improved following the
drought, the recovery was not nearly as great as that of winterfat and
shadsceale.

INFLUENCE OF GRAZING INTENSITY
ON VEGETATION

The great fluctuations in plant growth due to differences in precipita-
tion from year to year tend to overshadow the effects of grazing,
particularly during short periods of time. To segregate one effect from
the other, it is necessary to compare results obtained under different

28 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

intensities of grazing where other conditions, such as the amount of
precipitation received and the initial kind, distribution, and amount
of vegetation, are as nearly alike as possible. The period of comparison
should be of fairly long duration, since the effects of grazing are cumula-
tive, usually being small at first and becoming discernible or even
subject to analysis only after a considerable lapse of time.

Vegetation at the Desert Experimental Range was studied primarily
as it occurred within the fairly large subtypes characteristic of winter
range. These vegetal groups provide convenient units for the observa-
tion of changes in relation to grazing intensity. Even more important,
they are natural subdivisions within which grazing practices may be
modified to bring about improvement in the plant cover.

SHADSCALE AND WINTERFAT SUBTYPES

Effects of grazing intensity on the shadscale and winterfat subtypes

were studied in the experimental range pastures where the vegetation
was composed primarily of three subtypes, namely, shadscale-winterfat-
grass, shadscale-grass, and winterfat. Each of these three subtypes
were represented in some of the range pastures under each of the three
intensities of grazing. During the experimental studies the sheep
grazed the entire area of the range pastures and did not noticeably
show preference for any of the plant subtypes. Estimates of herbage
yield were made yearly for all species found on the range pastures.

See

PRECIPITATION CINCHES J)

HERBAGE PRODUCTION C€ POUNDS PER ACRE )
°

O
1935 1937 1939 194] 1943 I945 1947

Figure 12.—Average herbage production in October of the major grasses—Indian
ricegrass, galleta, and sand dropseed—in the 20 experimental pastures in relation
to rainfall during the preceding 15 months, 1935-47.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 29

Yield trends, for total herbage and for individual species under light,
moderate, and heavy intensities of grazing, were computed by the
least-squares method described by Snedecor (18).

TOTAL PRODUCTION

Total annual herbage production of all plants within shadscale and
winterfat subtypes as represented in the experimental range pastures
for the three intensities of grazing is shown in figure 13. Total pro-
duction is the sum of the increases and decreases of individual species
and therefore shows the over-all average difference between grazing
treatments.

~ When the studies were begun in 1935, average herbage production
in the range pastures assigned at random to light and moderate grazing
was somewhat lower than in those assigned to heavy grazing. Initial
yields, calculated from density estimates, were 232, 271, and 286
pounds per acre, respectively, for light, moderate, and heavy grazing.

Herbage production dropped during the next 2 years under heavy
grazing. Production also showed a decline under light and moderate
grazing in 1937 following a year with below-average precipitation.
Yields under all three intensities rose in 1938 after favorable precipita-
tion. In every year following 1938 more herbage was produced on the
moderately grazed range than on that heavily grazed, despite the fact

300

200

HERBAGE PRODUCTION (POUNDS PER ACRE )

O
1935 1937 1939 194] 1943 1945 1947

Figure 13.—Average annual herbage production of all plants and calculated trend
of production in 6 lightly, 7 moderately, and 7 heavily grazed range pastures
within shadscale and winterfat subtypes, 1935-47.

30 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE _

that the initial production was 15 pounds per acre lower. Under light
grazing, yields increased enough to overcome the original deficit of 54
pounds per acre and remained above those on the heavily grazed range
except for a slight deficit in 1944.

It is especially noteworthy that, during the 5 years from 1939 to
1943 which included 4 years with below-average precipitation, yields
under moderate grazing exceeded those under heavy. In 1943 after
2 years of drought, total production dropped to its lowest point under
all grazing intensities, being 84, 83, and 58 pounds per acre for light,
moderate, and heavy grazing. Herbage yields under light and mod-
erate grazing thus were 45 and 43 percent greater than the yield under
heavy grazing.

Calculated yield trends for the period of study are shown as straight
lines in figure 13. They were upward for all three intensities of grazing,
but more so for hght and moderate grazing than for heavy grazing—
54 and 46 percent as against 34 percent for the 13-year period.

Increases in total herbage production under light and moderate
erazing as compared with heavy grazing are not easily detected on
winter ranges. The results at the Desert Experimental Range, how-
ever, are comparable with those obtained on other classes of rangeland
where production is generally higher, such as the spring-fall sagebrush-
wheatgrass ranges in Idaho (4, 13), yearlong shortgrass range in
Montana (23), and black grama range in New Mexico (10).

INDIVIDUAL SPECIES

Yield of the major forage plants during the period of study under
each intensity of grazing is givenintable7. For effective interpretation
of yield trends under the three intensities of grazing, it is important to
consider the average utilization that each species received (table 5).

Winterfat showed the greatest changes in relation to grazing intensity
during the 13-year period of study (fig. 14). Under moderate grazing
this species made the greatest increase, and because of its relative
abundance it was largely responsible for the increase obtained in total
herbage.

Initial yields of winterfat, as calculated from density estimates,
were 19, 53, and 96 pounds an acre in the range pastures assigned to
light, moderate, and heavy grazing. Despite these great initial dif-
ferences, production under moderate grazing increased enough to
surpass that under heavy grazing in 1939. During the next 3 years,
yields were about equal for both intensities, that for moderate grazing
being slightly below heavy. After. the second successive drought year
in 1943, yields under moderate grazing again exceeded those under
heavy grazing and remained above in the last 4 years of study.

Yields of winterfat under light grazing were generally upward, with
declines during the dry years. The rate of recovery was slow, which
is not surprising in view of the low initial production.

Calculated yield trends of winterfat for all treatments, also shown
in figure 14, were upward—239, 321, and 33 percent, respectively—
for light, moderate, and heavy grazing. Average utilization of winter-
fat herbage for the 13-year period was 49, 55, and 66 percent. The
heaviest use occurred in the low production years from 1939 to 1943.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 31

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a2 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

/\ — Lay
a oat HE
UNAS ait

te)
1935 1937 1939 1941 1943 1945 1947
Figure 14.—Average annual herbage production of winterfat and calculated trend
of production in 6 lightly, 7 moderately, and 7 heavily grazed range pastures,
1935-47.

HERBAGE PRODUCTION CPOUNDS PER ACRE)

Yield of shadscale, the most abundant species, showed upward trends
under all intensities of grazing. The trends were slightly greater with
moderate, and considerably greater with light grazing than with heavy.
This was probably because more of the seed was eaten on the heavily
grazed range, thus decreasing the amount of reproduction. Average
utilization under light, moderate, and heavy grazing was 20, 21, and
28 percent; plant vigor was therefore probably not diminished at any
intensity.

Indian ricegrass showed little trend in relation to the different degrees
of grazing. In these subtypes it makes up only a small proportion of
the vegetation and was overgrazed at least in some years in all pastures.
Average utilization under light, moderate, and heavy grazing was 65,
76, and 88 percent. The trend in production was downward for all
three degrees of use to 1943. In the dry years of 1942 and 1943 yields,
although generally low, were slightly higher under light and moderate
use than under heavy. The rate of recovery after 1943 was somewhat
more rapid under the first two intensities.

Galleta yields were greater in all years under light and moderate
intensity than under heavy . The three intensities ‘showed respective
downward trends of 27, 14, and 35 percent. The differences between
trends were not statistically significant. Average utilization was 20,
49, and 67 percent under light, moderate, and heavy grazing. Only
in the years of 1939 and 1941, when favorable summer rainfall occurred
and production increased, did differences ascribable to grazing treat-
ment emerge. In both of these years production increased more with
light and moderate grazing than with heavy grazing.

Production of sand dropseed also showed slight downward trends
for all grazing treatments, although this species was utilized only 9,

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 33

24, and 40 percent under light, moderate, and heavy grazing. Bud
sagebrush and other minor species, including all forbs, did not show
any consistent trend in grazing intensity during the period of study.

SHADSCALE-INDIAN RICEGRASS SUBTYPE

A shadsecale-Indian ricegrass subtype was divided by fencing when
the experimental range was established in 1934. This subtype extended
from inside the northeast corner of the fenced allotments of the experi-
mental range into the unfenced range beyond. On both areas the
vegetation was badly depleted and production was low. Amounts of
herbage and usable forage were recorded in 1937 after the two areas had
been subjected to grazing at different levels for 4 years (table 8).

TaBLE 8.—Production per acre of air-dry herbage and forage within a
shadscale-Indian ricegrass subtype after 4 years’ grazing at moderate
and heavy intensities, 19357

Moderate grazing | Heavy grazing
Species | 7 Se
Herbage | Forage Herbage | Forage
Shrubs: Pounds Pounds Pounds Pounds
Dm dSealem tee ees 152.5 BO. L 148.4 Bias
‘Blackesazebrush= =e Sse yo NS 11.5 shal 2.9 es
Nalin Ge Tpley re ts oe er 30.7 18.4 4.5 26%
OGhemmisc ete eae 12.8 3.8 | Dili O| 6.5
All:shrubs:= 2 22 2: 207) 5 | 68.4 | 176.9 | 48.1
Grasses: |
Ingiannicesnasss=22 83 Ue aes te 166.7 | 125-0} S14 23.6
OGiner Besa See es | 14-8 | 4.4 | 1.4 A
INE OTaSSCs see eens es 13165 WB) ae | 32.8 24.0
ROD Ses sees oS 8 ie Sh (1) (1) | (2) @)
Ro tial metas Se S52 389 .0 197.8 | 209.7 72.4

1 Less than 0.1 pound per acre.

By 1937, after 4 years of grazing treatment, total herbage production
on the moderately grazed experimental range area was almost twice as
great as on the adjacent heavily grazed area. Production of the
palatable species—winterfat, black sagebrush, and Indian ricegrass—
was far greater under moderate grazing. Black sagebrush produced
about five times more herbage and winterfat almost seven times more
on the moderately grazed range than on the heavily grazed.

In 1934, a drought year, Indian ricegrass produced about 30 percent
of the total herbage. By 1937 it produced 167 pounds of herbage per
acre, more than 40 percent of the total within the moderately grazed
area, but it produced only 31 pounds per acre or about 15 percent of
total herbage yield under heavy grazing. The great increase under
moderate grazing made Indian ricegrass by far the highest producer of

34 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

forage within this subtype. ‘This improvement is in marked contrast
to the results obtained on the winterfat and shadscale subtypes where
Indian ricegrass formed a much smaller proportion of the plant cover.

In 1942 when further comparisons were made, Indian ricegrass was
still the highest producer of forage on the moderately grazed shadscale-
Indian ricegrass subtype. ‘The number of plants per unit of area was
about 50 percent greater than on the heavily grazed range. Fifty
plants were harvested at random from both the moderately and heavily
grazed portions of the subtype and compared (fig. 15). Those from the
moderately grazed range averaged 131% inches in height and prcduced
17.7 grams of air-dry herbage per plant as against 1014 inches and 6.7
grams for those from the heavily grazed range. Seed production was
3.2 times larger under moderate grazing than under heavy.

F—425597

Figure 15.—Fifty Indian Cees plants harvested at random from heavily grazed
range (top and third rows), and fifty from moderately grazed range (second and
bottom rows) in the shadscale-Indian ricegrass subtype.

The more abundant and better-filled seeds produced by vigorous
plants obviously favor the establishment of a greater number of seed-
lings. In the case of Indian ricegrass, however, years of good seed

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 30

production are very infrequent. They occurred only twice during the
13 years of study—in 1937 and 1941—when spring and summer rainfall
was greater than usual. To insure the survival and growth of seedlings
under such circumstances, moderate rates of stocking are virtually
mandatory not only after establishment but before (fig. 16).

F-—427012

Figure 16.—Many Indian ricegrass seedlings became established on this deteriorated
winter range after 4 years of conservative grazing and a favorable seed year in 1941.

BLAcK SAGEBRUSH SUBTYPES

In 1934 a large range area in Antelope Valley that was potentially
a black sagebrush-winterfat subtype was divided and one part of the
area was fenced. At the time of fencing the two parts were essentially
similar, the vegetation consisting primarily of winterfat and small
rabbitbrush, with small amounts of black sagebrush and grass (table 9).
One part was placed under moderate grazing while heavy grazing was
continued on the other part. Herbage production was recorded for
these two areas in 1934, 1938, and 1947.

Following 1934, a year of low rainfall, yields of herbage on both the
moderately and heavily grazed parts of the subtype increased. How-
ever, the computed yields of forage show a marked increase under
moderate grazing. The yield was twice as large in 1938 and more than
three times as large in 1947 as that produced in 1934. Meanwhile, the
amount of usable forage on the heavily grazed area remained practically
unchanged (fig. 17), despite the increase in total herbage. The esti-
mates of usable forage were obtained by multiplying the herbage yield
for each species on the area by its utilization percentage listed in table 1.

The pronounced increase in forage on the moderately grazed range
was brought about largely by a shift in the species composition and by
a higher total production. Herbage production of most of the palatable

36 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

F—468701

FiGuRE 17.—By 1947, after 13 years of moderate grazing, black sagebrush was the
dominant species on moderately grazed range (left). Vegetation on heavily grazed
range (right) was still characterized chiefly by small rabbitbrush.

species increased and that of the undesirable small rabbitbrush declined.
The greatest recovery was made by black sagebrush. In 1934, yield
of this highly palatable species was 21 pounds per acre, only 7 percent
of the total herbage. By 19388 its production had more than doubled,
largely as a result of increased vigor of the existing plants. In 1947
it produced 296 pounds per acre, almost 15 times as much as in 1934.
A large part of the increased yield during this latter period came from
the establishment and growth of a large number of seedlings. Through
this recovery and improvement black sagebrush became the most
important forage species, producing about 438 percent of the herbage
and 48 percent of the forage. In contrast, black sagebrush remained a
minor species on the heavily grazed range.

Yield of winterfat, the most productive species in 1934, doubled by
1938 under moderate grazing. Thereafter this species declined as black
sagebrush increased. But, in spite of the decrease, the yield of winter-
fat in 1947 was about 50 percent greater than in 1934. On the adjacent
heavily grazed range winterfat decreased about 15 percent below the
1934 yield.

Small rabbitbrush, an undesirable species which often invades heavily
grazed ranges, increased moderately up to 1938 and then decreased
drastically on the moderately grazed range. Under heavy grazing it
increased steadily and the yield in 1947 was 268 percent greater than in
1934. On the heavily grazed range it produced nearly one-half of the
total herbage in 1947. :

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 37

TaBLE 9.—Herbage production per acre within a depleted black
sagebrush-winterfat subtype in 1934 and after 4 and 13 years of
grazing under moderate and heavy intensities *

Tidal Moderate grazing Heavy grazing
Species Wieldsc |ascerae Fea all ERR rE
1934 1938 1947 1938 1947
Shrubs: Pounds | Pounds | Pounds | Pounds | Pounds
Black sagebrush —_ =< =_7 = 20.6 44.7 295.8 13.8 | 27.9
Small rabbitbrush__-__-___-_ 66.3 100.2 23).9 161.9 243.7
NWA Gertie = 32 ee ee 181.1 369.6 279.4 205.2 153.4
Others ies eo ee soe 3.0 (2) @) (2) (7)
‘Allishrubs-222 22.2% 271.0 514.5 603 .7 380.9 424 .6
Grasses: =
Galletak eGo ee ee tS a4 6.0 2.8 5.0 Beal
Indian ricegrass___-______- 9.9 14.8 40.9 11.1 18.6
NoUuEReltall ss ee ee on 4.1 28.3 13 4.5
Others se ees (2) (2) (2) (?) (2)
All grasses____-__- 16.4 24.9 7220 17.4 26.2
Forbs:
Globemallow___--______-_ (2) 4.8 Zeal: (2) 4.8
Russian-thistle._-.-_____- (2) (2) 6.0 3.0 96.7
Otherstaaass Ge ee (2) 9 9 (2) 9
Mletonrbss. 3 = (2) De 9.0 3.0 102.4
Totals ses ee ees 287 .4 545.1 684.7 401.3 55302
Usable forage *_____ 2 V4 9 283 .9 433.1 160.8 168.0

1 Calculated from plant density data.
? Less than 0.1 pound per acre.
’ Calculated from utilization records.

Grasses increased more than fourfold under moderate grazing. The
greatest increases occurred in the palatable squirreltail and Indian rice-
grass. Yield of squirreltail in 1947 was more than nine times and that
of Indian ricegrass four times as great as in 1934. Although these
species made pronounced gains, they produced only about 10 percent of
the total herbage and 12 percent of the forage in 1947. These species
made little gain under heavy grazing.

Production of Russian-thistle on the moderately grazed range was
very low in all years. In contrast, yield of this species on the heavily
grazed range in 1947 was about 97 pounds per acre, one-sixth of the
total yield.

Additional observations on vegetal changes were made on a deteri-
orated black sagebrush-shadscale range in Snake Valley, 3 miles north
of the Desert Experimental Range. A 4-acre enclosure was con-
structed on the range in 1937 and herbage production of all plant species
was recorded on plots inside and outside in 1937, 1939, and 1947
(table 10). |

38 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

TABLE 10.—Herbage production per acre in an ungrazed enclosure and
on adjacent heavily grazed range within a black sagebrush-shadscale-
grass subtype at two intervals after establishment of the enclosure in 1937

Ungrazed Heavily grazed
Species eS SSS SS
1937 1939 1947 1937 1939 1947

Shrubs: Pounds | Pounds | Pounds | Pounds | Pounds | Pounds
Shadscales-==— ==. = 118.1 104.7 238 .9 120.3 168.3 319.3
Bud sagebrush__—____ 4.7 6.2 24.1 a) 3.4 6.6
Wantertat = = 11020 je 66.0 99.8 57 .4 32.6
Black sagebrush __- ___ 13.5 22.8 | 196.4 Tork 12.3 22.1
Other= 22 ee 522 5.9 16.0 3 1.5 16.4
All shrabs == =-== 2515 5\> 256. 7-- 54s 4a 2397-84242 9 397 .0

Grasses:

Indian ricegrass__ ___- 42.9 90.0 26.8 43.7 56.0 39.1
Galletaze=— = ee 16.6 FD 2.4 26.7 5.4 5.0
equirreltail = = s— = s DD 4.3 74.7 320 3.8 20.2
Other See ee a2, 4 6.3 =¢ 1.0 18.5
All grasses_______ 61.9 98 .2 110.2 14-0 4 66-2 $2.8

Rorbse Sse ee 1355 1.5 Biles: 10.8 13.8 26.3
otales 2. Se 326.9 | 366.4 | 683.4 | 325.2 | 322.9 506.1
Usable forage See lode 192.2} 339.2 152 2% 13727 180.7

1 Calculated from utilization records.

Yield of black sagebrush within the ungrazed enclosure rose from 13
pounds per acre in 1937 to 196 pounds in 1947, about a fifteenfold
increase. This species produced only 4 percent of the herbage in 1937
and 29 percent in 1947. On the heavily grazed adjacent range it still
comprised only 4 percent even though its total yield was about 50
percent greater in 1947 than in 1937. Approximately the same relative
increase in black sagebrush was obtained on the moderately grazed
range in Antelope Valley as in this ungrazed enclosure.

Bud sagebrush and squirreltail also made significant increases within
the enclosure, in contrast to smaller gains obtained under heavy grazing.
Shadseale also increased on both areas, but the increase was more
pronounced on the heavily grazed range. Shadscale frequently in-
creases on overgrazed ranges, especially where winterfat and black
sagebrush are injured by excessive grazing.

Grasses were quite variable in their response. Indian ricegrass in-
creased between 1937 and 1939 and then declined. Galleta declined
throughout the entire period. Squirreltail increased remarkably on the
protected area, from 2 pounds per acre in 1937 to 75 pounds in 1947.
The increase under heavy grazing was not so pronounced.

The estimated usable forage more than doubled between 1937 and
1947 in the protected enclosure, whereas on the heavily grazed range
forage production declined in 1939 and then increased in 1947, largely
as a result of fluctuation in precipitation. Yield of forage within the
enclosure in 1947 was almost twice as great as on the heavily grazed
range, yet total herbage was only 35 percent greater.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 39

WINTERFAT SUBTYPE CONTAINING RUSSIAN-LHISTLE

Although only minor quantities of Russian-thistle are present on
the Desert Experimental Range, it has heavily invaded many depleted
winterfat areas in valley bottoms elsewhere (fig. 18). In 19387 a 4-acre
enclosure was constructed on such a range in Pine Valley, 7 miles south
of the experimental range. At that time about 60 percent of the vegeta-
tion was Russian-thistle (table 11).

By 1940 Russian-thistle had almost disappeared within the ungrazed
enclosure, but on the surrounding range it had increased and in that
year produced 75 percent of the total herbage. Within the enclosure
in 1947, after favorable precipitation, production of this species was
only about 2 percent of the total. In contrast, it increased almost
fourfold on the adjacent heavily grazed range, where it produced 402
pounds per acre or 54 percent of the total herbage.

The unpredictable behavior of Russian-thistle is illustrated by its
wide yearly variations in production, even on heavily grazed range
where competition was lacking. In the dry year of 1946, it produced
only 0.7 pound of herbage an acre, an insignificant amount in compari-
son to the production of winterfat under the same conditions.

The continued suppression of Russian-thistle inside the enclosure was
brought about primarily by the increases in winterfat and Indian rice-
grass—both highly palatable species. By 1947 these two plants made
up 90 percent of the total herbage in the enclosure, whereas the total had
increased nearly 400 percent. On the heavily grazed range they pro-
duced only about one-half as much herbage as in the enclosure.

Indian ricegrass showed much the same general response in this
enclosure as it did under moderate grazing. From an initial low pro-
duction of about 3 percent of the total it yielded more than 25 percent
of the herbage by 1946. During the next year the proportion declined
to about 20 percent. This seems to be the characteristic reaction of
Indian ricegrass under reduced levels of grazing—a marked increase in
production at first and then a decline as the slower growing shrubs
recover and become reestablished.

F-415774
Figure 18.—A heavy stand of Russian-thistle on a deteriorated winterfat range.

40 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

Although the usable forage was slightly greater on the adjacent
heavily grazed range in 1937, 10 years later the estimated usable forage
produced within the enclosure was 373 pounds per acre as compared
with 224 pounds outside it. The heavily grazed range had the greater
total herbage yield in 1947, but more than half of this was the low-
value Russian-thistle, which showed a striking increase, largely because
of the unusually favorable precipitation during the preceding year.

TABLE 1|1.—Herbage production per acre in an ungrazed enclosure and on
adjacent heavily grazed range within a winterfat subtype at three intervals
after establishment of the enclosure in 1937

Ungrazed Heavily grazed
Species eee ee ee ee aan
1937 | 1940 | 1946 | 1947 | 1937 | 1940 | 1946 | 1947
Shrubs: Lb: Lbs |b. | 26. ibe) bs | be ae
Winterfat__.-------- 35.8 |171.4 |121.2 [428.1 | 49.0 | 29.1 | 61.7 | 213.8
Others ie ae [eb | ON | 22.47] 67 3312 a Oe
All shrubs_____- 36.3 |171.4 1123.6 [434.8 | 52.3 | 31.8 | 64°7 | 225.2
Grasses: | | = | |
Indian ricegrass _ _ _ -- £0) 18716 45-07 13274 del ae ea eae
Galleta: 12:1 | 49:8: 5.8 | 21-91 9:3 2.7.6 | 3 5 ease
Others = se 8 See) 2 150-|- 2.5 | 3) le a0 eae
All grasses ___ | 16.5 | 68.4 | 51.0 [155.3 | 14.9| 12.0 | 12.7] 84.0
Forbs: | |
Russian-thistle_____- 73.3} °2\ 0 | 18.9 1113 21143 0 | 78 a0ieG
Giicr = os 3.21 10:4 4118 0 118-20 oe eee
AM forbs == = s)\27665.1 1006 4 | 31.9 [115.0 [145.7 | 2.5 | 438.9
otal 8 129.3 |250.4 |175.0 622.0 [182.2 |189.5 | 79.9 | 748.1
Usable forage ?__| 38.0 141.2 |109.7 |372.7 | 49.1 | 39.5 | 44.8 | 223.6

1 Less than 0.1 pound.
2 Caleulated from utilization records.

INFLUENCE OF GRAZING INTENSITY
ON SHEEP PRODUCTION

Concurrently with the studies of herbage yields and vegetal changes,
data on sheep production were maintained. Records of body weight
were made for all ewes assigned to the experimental range pastures.
Additional data on body weights of ewes together with information on
wool vields, death losses, lamb crops, and income were obtained for the
two herds (designated as A and B) that grazed in alternate years on the
experimental range allotments and on nearby unfenced range. Further
records included observations on supplemental feeding of both these
herds as well as others grazing in the vicinity of the experimental range.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 41

SHEEP PRODUCTION ON RANGE PASTURES

Changes in body weight of ewes kept in the 20 experimental range
pastures were recorded during each grazing season from the winter of
1937-38 to 1943-44. The sheep were weighed at the beginning of each
grazing period—early, middle, and late winter—and at the end of the
winter grazing season. ‘The number of ewes assigned to each range
pasture was varied each year in order to achieve the desired intensity of
grazing on the basis of the expected herbage production estimated in
October.

The sheep were allowed to graze freely without herding. They had
access to snow or water every day. When snow was not readily avail-
able, water was trucked to the ranges and placed in troughs. The
sheep were bedded in different locations from time to time and the
troughs were moved frequently to aid in obtaining uniform utilization
within the range pastures. During cold weather it often was necessary
to break and remove ice from the troughs so the sheep could drink.

Average changes in body weight of ewes that were kept throughout
the winter season on the range pastures are shown in figure 19 for the
6-year period during which records were maintained. Ewes kept
throughout the winter on lightly or moderately grazed range showed
a net gain in each of the three winter grazing periods. The gains under
moderate grazing in the first two periods exceeded those made on
lightly grazed range. In the late winter period, ewes under light
grazing gained slightly more than those under moderate. Total net
gain for ewes under moderate grazing (11.4 pounds) was well above that
for ewes under light grazing (8.5 pounds). Ewes in the heavily grazed
pastures lost weight during the early and midwinter periods but gained
about 2 pounds per head in the late winter period when early green
growth of the forage plants became available. The gain during the
late winter period under heavy grazing was less than half the gains
made under light and moderate grazing, and was insufficient to offset
earlier losses.

The weights reported do not completely measure actual flesh con-
dition of the animals. Ewes weighed at the end of the winter grazing
season bear between 4 and 5 pounds more wool than at the beginning.
Many of those a year or more old are carrying lambs which, together
with fetal tissue and liquid, weigh 10 to 15 pounds by spring. Pregnant
ewes that weigh the same in spring as they did when they reached
winter ranges may therefore have lost 15 or 20 pounds in flesh when
deductions are made for current wool growth and unborn lambs.
Much wider variations in weight occurred in the late winter period than
in the other two. This was probably because of differences in weight
of fertile and barren ewes and differing stages of pregnancy of the
fertile ewes.

The kind and amount of forage produced on range areas influenced
sheep weights considerably. Ewes in the lightly grazed range pastures
10 and 11, where vegetation is primarily sand dropseed and shadscale
with very small amounts of winterfat, showed approximately 2 to 3
pounds less gain than those in other moderately or lightly grazed
pastures. Sheep made the greatest gains on areas where wintertfat,
Indian ricegrass, and bud sagebrush produced 30 percent or more of
the forage.

42 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

Weight changes throughout the winter grazing season were also
influenced by the condition of the sheep when they reached the winter
range. In years when summer and fall forage was inadequate and dry,
many sheep arrived on the winter range in rather poor condition.
These animals usually failed to improve much even on moderately
grazed range.

To determine the interrelated effects of grazing intensity on sheep
condition from one winter period to another, a special study was made
in 1940-41 and 1941-42. Fifty-four ewes of two age classes—27 three-
year-olds and 27 four-year-olds—were carefully selected for uniformity
of size and condition, at the beginning of the winter grazing season.
These sheep were randomly assigned to 9 range pastures in such a way
that one sheep from each age class was subjected to each of the 27
possible grazing treatments involving the 3 winter grazing periods and
3 grazing intensities.

Bs HEAVY GRAZING

10
S RY MODERATE GRAZING
8 : YOe,
/ OY
S | gL MA ticnut crazine iS Y
© SM,
== Kx
= recon
cer A SG
my RS Y o ZY
RX YO
: ZF wees
2 Sees eZ
2 sess iG
= Soces RX]
Sees rene
ly See KX
S | 2 SZ ee
: BY BR
x SY, YG
Se SZ SZ
%
»
9
~ 2
EARLY MIDOLE LATE TOTAL
WINTER WINTER WINTER

Figure 19.—Average changes in body weight of ewes that grazed experimental range
pastures throughout each grazing season at light, moderate, and heavy intensities,
1938-39 to 1943-44, inclusive.

These treatments are shown in figure 20. For example, 7 pairs were
in lightly grazed pastures two or more periods, of which pair No. 1 was
in lightly grazed pastures during all three winter periods; pair No. 2
was in lightly grazed pastures in the early and middle periods and in
moderately grazed pastures in the late winter; and pair No. 7 was in
heavily grazed pastures in the early period and in the lightly grazed
pastures in the other two periods.

Averaged data for the light grazing treatment show that ewes gained
a total of 8.4 pounds per head — 3.2, 1.4, and 3.8 pounds per head
respectively for the early, middle, and late winter periods (fig. 20).
The average total gain for moderate grazing was 13.0 pounds per head.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES

LIGHT GRAZING TWO OR MORE PERIODS

HEAVY GRAZING TWO OR MORE PERIOOS

MODERATE GRAZING TWO OR MORE PERIODS

AAAS) S
IN RQ WAAAA\K\ S NY

MOA < SSNS
SN
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ve es ~

(SONNOd): FONVHD LHOIFM AGOG

Y GRAZING ONE PERIOD EACH

—

op MODERAT

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CS
IG
lu
Sa
a3
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a
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fi
gz
E Bs
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lus 9
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aq

LIGHT MODERATE HEAVY
EARLY WINTER

PAIR NO. 6

|
A

PAIR NO. 4

PAIR NO

LEGEND

PAIR NO. 7

PAIR NO. 5

PAIR NO. 2

+
=

PAIR NO. 3

Figure 20.—Average changes in body weight of two ew
tures for all grazing periods and in

In range pas-

es each season
, 1940-41 and 1941-42.

tensities

44 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

In contrast, sheep in heavily grazed pasture failed to gain. These
results are quite similar to those already reported for other sheep in the
pastures. Ewes that were on moderately or lightly grazed range for
two or more of the winter periods gained two to three times as much as
those on heavily grazed range for two or more periods. Sheep that
remained vigorous and in good condition through one period of heavy
grazing frequently gained rapidly the following period if they were
placed on moderately or lightly grazed range. An example of this is
pair No. 6 of the set that were on moderately grazed range for two or
more periods. The pair was on moderately grazed pasture in early
winter, on heavily grazed pasture in the middle winter period, and on
moderately grazed pasture again in late winter. Although the pair
lost an average of nearly 2 pounds during the middle period, it made
an average gain of 9 pounds during the late period.

Sheep under moderate grazing often gained more than those in the
lightly grazed range pastures. This may be partly because herbage
production and plant composition in the various pastures differed, and
partly because the sheep in smaller groups using the lightly grazed
areas were more restless and discontented than the larger groups of
sheep in other range pastures.

SHEEP PRODUCTION ON RANGE ALLOTMENTS

To compare differences in production between sheep on moderately
and heavily grazed winter range, two large experimental allotments
were selected and two full-sized winter herds of 2,500 to 3,000 sheep,
essentially similar with respect to breeding history and range opera-
tions, were used.

In 1935 the two experimental allotments were typical of neighboring
winter rangelands with respect to topography, vegetation, and range ~
conditions. Both of the allotments or range areas extended from the
valley bottoms to the mountains. For the most part, they had been
heavily grazed in previous years and were classed as in poor condition.
One of these was located on the Desert Experimental Range and the
other was on a similar adjacent range.

The allotment within the experimental range was moderately stocked
at an average rate of approximately 15 sheep-days per acre during the
period of the study, 1935 to 1947. The rates varied from about 27
sheep-days per acre in the most productive winterfat and black sage-
brush subtype to as low as 5 sheep-days per acre on the poorer sites in
the shadscale subtypes. The rate of stocking also varied from year to
year with herbage production.

Ordinarily the herd was placed on the moderately grazed experimental
allotment in early November as soon as it reached the winter range and
remained until late April. In years when forage yields were low the
sheep did not enter the moderately grazed experimental allotment until
late November or early December. The number of sheep-days feed
available each year was approximated on the basis of the changes in
herbage yields that were recorded in October in the range pastures,
and the dates of entry were varied accordingly.

Utilization was fairly uniform from year to year. However, from
the time the herd reached the winter range in early November until it
entered the moderately grazed allotment, adequate forage was available
on other parts of the general winter range. During 1935 and 1936

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 45

grazing was somewhat lighter than in succeeding years. Average
utilization of the various forage species for the period of the study was
practically the same as that reported in table 1. Although adjustments
in stocking were made, apparently they were not adequate to fully
compensate for the wide fluctuations in production. As a result,
utilization of the forage species was greater in years of low herbage
yields than in years when production was above average.

For the heavily grazed allotment exact records of stocking or grazing
use are not available because during the first 4 years of comparison the
allotment was used in common by several herds which grazed in mi-
gratory fashion over wide areas of winter range. Utilization during
this period was extremely heavy, the palatable species receiving prob-
ably one-third greater use than those on the moderately grazed allot-
ment. During the last 5 years the heavily grazed allotments were
assigned to individual sheep operators. Although this brought about
some reduction in grazing intensity, utilization of the palatable species
was still fairly heavy. The average intensities of grazing for the entire
period were estimated to be about one-fourth heavier than 1 in the mod-
erately grazed allotment.

In 1942 about half of the herd assigned to the heavily grazed range
was sold, leaving about 1,500 sheep. Because the two herds were no
longer comparable in size the detailed comparisons were discontinued
although some general phases of the study were carried on for a few
more years.

Sheep in both horde were range-bred Rambouillets of good quality
and essentially similar. The herds belonged to two brothers and had
been previously owned and operated jointly by their father. Operating
methods for both herds, designated A and B, were closely similar.
During the winter of 1935-36 herd A was placed on the moderately
_ grazed allotment within the experimental range and herd B was assigned
to the heavily grazed range. In succeeding winters the assignments
were reversed annually.

This alternating arrangement in grazing was used to eliminate dif-
ferences due to management, herd performance, and the cumulative
effects of previous grazing treatment which might be peculiar to the
individual herds.

Management practices for the two herds differed throughout the
period of observation. In the moderately grazed experimental allot-
ment they were as follows: (1) The allotment was divided into units
which were grazed at predetermined periods; (2) sheep were bedded in
a new location each night; (3) herding was carefully controlled to permit
quiet grazing and to check unnecessary trailing; and (4) water was
supplied every day or every second day when snow was not readily
available.

On the unfenced range, sheep were managed according to practice
customarily used on many of the winter ranges in the Intermountain
region: (1) The entire range area was grazed repeatedly as a single unit;
(2) sheep were bedded on established bedgrounds, often for several
nights in succession and often after trailing as much as 3 miles to reach
a particular site; (3) trailing and movement were seldom checked by the
herders; and (4) animals were primarily dependent on snow or reservoir
supplies for water, and sometimes had to be trailed as much as 4 miles
to get water during dry periods in early or late winter.

46 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

BODY WEIGHTS

Body weights of sample groups of ewes from herds A and B were
recorded over a period of 7 grazing seasons (table 12). Seventeen ewes
in each of seven different age classes were selected at random from each
of the herds. They were weighed at the beginning and at the end of
each winter grazing season.

Although some variations in the sheep weights were recorded each
fall, sheep in the two herds were fairly comparable in weight in every
year except 1943-44. In that year the sheep in herd A, placed on the
moderately grazed range, weighed only 110 pounds per head and were
visibly poorer than those in herd B which weighed 121 pounds per head
when they were placed on the heavily grazed range in the fall.

TABLE 12.—Average seasonal changes in body weight of 119 ewes in two
herds (A and B) eee alternately at moderate and heavy grazing
entensities, 1937-44

Pounds Pounds | Pounds Pounds | Pounds Pounds

103 36. L 118-9 122.6 | od. 116.4 | 111.8 —4.6
1938-392 = 2 114.7 122.3 | 7.6 113.7 | 108 .1 —5.6
1939—40_ __ __ 108.3 121.0 12.7 eH Fea 8 119.6 Bao
1940-41= | 121 124.9 | 12.8 | 110.1 | 113.3 | 3.2
1941-42. ____ TLE 129.8 | 18.1 113.0 | 124.2 11.2
1942-43 ____- 120.2 125.6 | 5.4 118.0 112.7 —5.8
1943-44_____ = 109-6] 114.0 4.4 121.1 | 122.5 1.4
Average... 113.6 | 122.9. 9.3 114.9 116.0 Le

1 Figures in italic type for herd A, others for herd B.

Sheep on the moderately grazed range under good management
showed an average seasonal gain of 9.3 pounds per head for the entire
period of study, whereas those on heavily grazed range with poor
management gained only 1.1 pounds per head. The 8.2 pounds dif-
ference between the two herds was nearly the same as that recorded
for the sheep in the moderately and the heavily grazed pastures where
the treatment and management were uniform. There were great
fluctuations in weight changes from year to year, primarily because
of differences in forage production and weather conditions. Notwith-
standing this fact, the sheep on moderately grazed range remained in
good condition and showed gains in all winters (fig. 21). Ewes on
moderately grazed range made greater gains in every year than those
on the heavily grazed range. “In three winters—1937-38, 1938— 39,
and 1942-43——when weather conditions were rather severe, sheep on
heavily grazed range showed net losses in weight.

In the concluding year of this phase of the study, half of herd B,
which was then on heavily grazed range, was sold. Although the re-
maining sheep had ample forage throughout the winter, much of it was

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 47

F-468700

FraurE 21.—Sheep grazing black sagebrush in an experimental allotment during the

early winter. The tall, nutritious forage plants in this allotment enabled ewes to
maintain themselves in good condition throughout most winters.

of low quality. Asa result the sheep gained an average of 3 pounds
less than those on the moderately grazed range. Differences in condi-
tion of the sheep in the two herds, when they reached winter range in
the fall, may also have influenced the weight gains.

Average weight changes in sheep by age class for the period of study
are shown in table 13. Sheep in each of the age classes were fairly
comparable as indicated by fall weights. The most actively growing
class, those under 1 year, naturally made the greatest gains in weight.
Gains for this class under moderate grazing, however, were twice as
great as under heavy grazing. Breeding ewes (those 1 year old or
older) on moderately grazed range gained approximately 9 pounds per
head, whereas those on heavily grazed range made a gain of only 0.4
pound or one-twentieth as much. Under heavy grazing ewes 6 years
old or older showed a net loss of 0.5 pound in body weight. In severe
winters the greatest loss occurs in ewes over 6 years of age and in the
young sheep less than 1 year old. ‘The old ewes on heavily grazed
range lose weight rapidly, especially in cold weather, and become poor
and weak.

Trends of weight changes of the sample ewes in herds A and B during
the grazing seasons of 1937-38 and 1938-39 are shown in figure 22. In
these years weights were recorded at several intervals throughout the
winter. Weather in the winter of 1937-38 was rather severe and
grazing was difficult for both herds. During part of the winter of
1938-39 weather conditions were likewise severe. In spite of this
the sheep remained in good condition because they had access to the
excellent forage crop that was produced the previous summer. In both
years, however, ewes on moderately grazed range showed net gains in
weight at the end of the season, whereas those on heavily grazed range
lost weight rapidly during the midwinter period and failed to gain
enough in the late winter to offset the loss.

48 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

MODERATE
ome == HEAVY

OCT. NOV. DEC. JAN. FEB. MAR. APR.
1937-38

CHANGE IN WEIGHT (POUNDS)

OCT. NOV. DEC. JAN. FEB. MAR. APR.
1938-39
Figure 22.—Changes in weight of 119 ewes in herds A and B, which were wintered

alternately on moderately and heavily grazed ranges for the grazing seasons of
1937-38 and 1938-39.

During the first part of the winter period both herds showed about
equal weight trends. Apparently there was sufficient forage for the
flock on the heavily grazed range until sometime in January. Then
the two herds began to show differences in body weight. Since the
ewes were bred during December, fetal development undoubtedly in-
fluenced the body weight of ewes throughout the winter. During the
midwinter period ewes on moderately grazed range gained in body
weight. In contrast, the ewes on heavily grazed range continued to
lose weight until sometime in March. The differences in body weight
on the moderately and the heavily grazed range were similar in most
years of the study.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 49

TasBLe 13.—Average fall and spring weights and change in body weight
by age classes of 119 ewes in two herds (A and B) wintered alternately
at moderate and heavy grazing intensities, 1937—L4

Moderate grazing Heavy grazing
Age class
Fall Spring | Change in Fall Spring | Change in
weight weight weight weight weight weight
Pounds Pounds Pounds Pounds Pounds Pounds
Under | year 23 83.4 Pet 73.0 (821 5.1
1-year-olds___ 105.6 114.4 8.8 111.8 113.1 33
2-year-olds___ 118.3 128 .2 9.9 118.4 118.6 0.2
3-year-olds___ 120.9 130.8 9.9 123.8 124.5 ath
4-year-olds___ 127.6 135.8 8.2 125.9 126.8 a)
5-year-olds___ 126.1 D583) 9.2 126.3 126.4 ma
6-year-olds
and over_-.- 124.2 132.3 Sou 125.0 124.5 —.5

During the unfavorable winters of 1937-38 and 1942-43, ewes on
heavily grazed range suffered losses of as much as 20 to 25 pounds in
body weight. These drastic losses often left the animals so weak that
many were unable to survive the long trailing and trucking necessary
to return them to the spring shearing and lambing ranges.

WOOL YIELDS

Fleece weights of all sheep that wintered on the experimental allot-
ments were obtained after spring shearing from 1936 to 1943. The
averages for herds under the two treatments are shown in table 14.
Weights given are on the ‘grease’ or ‘‘dirt”’ basis before the fleeces
were washed.

Average fleece weights were greater in every year for the herds that
grazed at a moderate level. The difference varied from a low of 0.24
pound per head after the winter of 1935-36 to a high of 1.67 pounds
after the winter of 1936-37, and averaged 0.95 pound for the period
of observation.

The greater fleece weight of the sheep on the moderately grazed
areas is attributable to the larger amounts of nutritious forage they
consumed. A previous study in New Mexico has presented evidence
that the plane of nutrition has a marked influence on wool yields, and
that well-fed sheep produce more wool than underfed ones (22).

DEATH LOSSES

Observations on winter death losses were made on herds A and B
during the period of study. Death losses among the sheep on the
moderately grazed range averaged 3.1 percent, of which about 2 percent
were killed by coyotes and the remainder died from unknown causes.
Death losses of sheep on heavily grazed range were more than double
with an average of 8.1 percent, of which a little more than half was
due to causes incident to malnutrition and the rest to coyotes and

50 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

unknown causes. Occasionally after winters of very short feed, es-
pecially when weather was cold and the snow deep, sheep on the
heavily grazed range became very weak by spring and losses were
extremely high. In 1932, after a severe winter, losses of 10 to 20
percent were common on heavily grazed ranges in the general vicinity
of the Desert Experimental Range; some herds suffered losses as high
as 50 percent.

TABLE 14.—Average fleece weights from two bands of sheep, one on
moderately grazed range and one on heavily grazed range 1935-36 to

1942-43»

: Moderate Heavy :
OEE season Sess oe Difference
Pounds Pounds Pounds
POSS G0. a5 ee ee a ee ee eT Eh 10.91 0.24
1936-3 6 eS a ee eee 10.79 | 9.12 1.67
$937 38 eS ee ee ee ee 10.70 | 10.16 | 54
{OS R30 Se 2 eS Se ee 10.94 | 9.28 | 1.66
193 FA ae OS a a oe 10.51 | 9.33 118
POAQHA se ee ee eee 39.58 | 9.53 .05
P9411) Se ee ee a Se ee 10.67 9 02 1.65
PQA A So SS Ee ee ee ea 10.67 | 10.10 57
AVOTA SC eS ie iS 10.63 9.68 | .95

1 All weights on “‘grease” basis; averages from 1939-40 onward adjusted to uniform
shrink (approximately 61 percent).

2 Figures in italic type for herd A, others for herd B.

3 Losses of approximately 1 pound per head in sagebrush range prior to shearing not
included.

LAMB CROPS

Lamb crops of herds wintered in the moderately grazed allotments
and on heavily grazed range were recorded between 1935 and 1946.
Counts of lambs were made at docking time. Data from these counts
are shown below in terms of the number of lambs docked per hundred
ewes.

Lambs produced

per 100 ewes
Moderate H eavy
Grazing season: acon (amber

OS 5=50 22 es re ee ae ee Shae a eee ees 75 70
POSG has Se Se ee ee ad glen 5 sj ees he 76 69
SUSIHSS = FE de Soe Nee aah eee ee See Ee 73 7
POSS OO se Oe a Be ae Ey ae he eee 86 65
TAO ee IT et ee ee 87 92
PAG 4452 BSI Se a ae ee ee eee 106 78
1 YY Ree. 5 a eed a ee A ere Ae a Ry ee Le ae eS SP 92 84
jE Ee. © sea Da aR Ree crt Beg gis Cope ipa AS a Ps vay Say Fe TL 94 87
ET ee NS ee gar a a Oe ae 73 85
ae eo EE SS ee ee ee 104 67
SOAS 46 St Se ee a ee 98 93

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 51

I-wes that wintered on moderately grazed range usually produced
more lambs the following spring than those that wintered on heavily
grazed rarge. Following the winter grazing seasons of 1937-38,
1939-40, and 1948-44 more lambs were docked from the herd which
wintered on heavily grazed range. In spite of this disadvantage the
herd on moderately grazed winter range produced, on the average, 11
percent more lambs than the herd that wintered on heavily grazed
range. Lambs at market time were also slightly heavier.

SUPPLEMENTAL FEEDING

Practices in regard to the feeding of supplements vary somewhat
on the winter range. A few herds are fed supplements throughout each
winter. Most herds, however, are fed for a short time only in the late
winters when forage is unusually scarce and the condition of sheep is
noticeably poor. Occasionally entire herds are fed in this manner, but
in most cases only the poorer sheep are given supplements in separate
bands.

As arule such feeding begins about January 15 and continues through
March or April or until green forage becomes available. Sheep are
usually fed 14 to 1 pound per day of cottonseed cake, grain pellets, or
corn.

During the period of study, sheep within the moderately grazed
experimental allotment wintered in good condition even in severe
winters without any supplemental feed. Sheep on the heavily grazed
range were fed some supplements for short periods during a few of the
severe winters. The usual practice was to feed only the poorer sheep.
Although they received this supplemental feed, many of the animals
still lost weight and death losses were heavy. Several other herds on
adjacent heavily grazed range were fed considerable amounts of cot-
tonseed cake or corn during 3, 4, or 5 years to help carry the sheep
through periods when range forage was inadequate. In the fairly
severe winter. of 1936-37, these herds were fed cottonseed cake during
a period of 4 to 6 weeks. Nevertheless, many of the ewes remained
in poor condition and death losses were high.

Studies in recent years have shown that many of the winter range
forage plants are low in nutritional and mineral content (3, 5, 6). It
is therefore probably desirable to feed supplements in most years to
supply dietary deficiencies even for sheep on moderately grazed areas.
Some experiments to determine what supplements may be necessary
are being conducted at the Desert Experimental Range in cooperation
with the Utah State Agricultural College. These studies show that
most of the forage plants are deficient in phosphorus and that condition
of sheep is markedly improved when they are fed supplements contain-
ing this element.

INCOME

Financial and operational data were obtained for herds A and B
covering 8 years. These data were combined for each type of grazing
treatment. Since the herd sizes varied, figures were recomputed on the
basis of 3,000 head to make them directly comparable (table 15).

o2 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

TaBLE 15.—Average production and income of herds on moderately and
heavily grazed range, 1935-43}

Tem Moderately Heavily
grazed range | grazed range
WES 6G) Gs pots ee ee number_-_ 297 207
Income trom: ewess) = Ss ee $891.00 $621 .00
Breeding ewess2 5" 222. See 3s ee number- - 2,610 2,900
Bam bocropess 2a ae eh ees ee ee d@_=== 2,297 2,015
bambstheld 523). 5 ee ee des2= 390 450
Tambs sold 232 ee ea eee doLe= 1,907 1,565
Weight-ob lambs sold-2= ee pounds_- 143 ,025 109, 550
Hale. price per pounds. =e. ee ee $0 .085 $0.08
Income tromstam bso se Pe Piel Oo ielS $8 , 764.00
Ewes sheared_-_-_-_-___ pee Soe tet een bee number _-_ 2,953 , 2,878
Rleeceswelrht.= 22 2 6 se pounds_- 10 9
Wroolsproduceds¢ so Ss 2 ese oe ee dose) 29,530 25 , 902
Income from _wool!.= t-te ee eet ete TO oo eOU $9,065.70
Incomes rom: peltss2< 2 ae eee $46 .50 $121.50
(GhOSSaN COM Se a es ee | $23,430.13 $18,572.20
Costs 3s ee ee a Se ee $13,050.00 $13,500.00
ING tINCOMC Ses 2 es a ee | $10,380.13 | $5,072.20

|
i

-—

1 Data for herds A and B, which grazed alternately on the two areas, combined by
treatment and recomputed on the basis of 3,000 head.

2 Sale price of wool $0.35 per pound.

3 All operating costs, including taxes, replacements, labor, feed, and miscellaneous.

Costs of operations and prices received are those that prevailed during
the period of the study. Wool sales were not uniform for the two herds.
In some years the wool was sold; in other years one or more of the op-
erators shipped it on consignment to Boston. To eliminate the
difference in sale method and prices obtained for wool, $0.35 per pound
was used to compute the income for wool for the two flocks. This is
approximately the average sale price of wool prevailing during the
study. Higher prices and operational costs now prevailing would no
doubt affect the total income. However, the comparisons between
moderate and heavy grazing would be proportionate to the values given.

Average net return from the herds on moderately grazed range was
slightly more than twice as great as that from the herds on heavily
grazed range. Annual net income per head from moderate grazing was
$3.46 as compared with $1.69 per head for heavy grazing.

The greater net return on the moderately grazed range areas was
directly attributable to the generally better conditions of the sheep
there. Death losses were lower, fewer lambs were needed for replace-
ment, and a greater number could be sold. The herds on moderately
grazed range also had a larger number of breeding ewes. Because of
these interrelated factors these herds produced for market 31 percent
more lamb, 43 percent more mutton, and 14 percent more wool. In
addition lambs, being approximately 5 pounds heavier, sold on the
average for one-half cent more per pound.

Costs of operation during the period of study were greater in all
years for the herds that grazed at heavy intensity. This was primarily
because of increased expenditures for ewes in poor condition, including
trucking and feeding costs. The greater replacement costs after heavier

™

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 953

death losses formed another item of expense which reduced the net
income from the herds on heavily grazed range.

These studies show that production of both sheep and forage are
improved under moderate grazing and good management. They also
show that income Is greatly reduced by heavy stocking. This is also
borne out by results of an economic study of sheep enterprises in south-
western Utah (2), where it was found that income per ewe was not
associated with size of enterprise or number of sheep owned but rather
with lamb and wool yields. Although management practices and in-
tensities of grazing use were not evaluated in that study, they un-
doubtedly had considerable influence on lamb and wool production.
A study of 8 ranches in New Mexico (14) has also shown that the great-
est production of wool and lambs was obtained where moderate grazing
levels were maintained in conjunction with good management practices.

GUIDES FOR INCREASING FORAGE AND
SHEEP PRODUCTION

The investigations at the Desert Experimental Range have shown
that forage production on ranges in depleted condition can be increased
under moderate grazing use by sheep. Such use must be in balance
with the potentialities of various range areas to produce forage. To
assess this potentiality requires knowledge of the composition of the
vegetation and present condition of the range. With this basic knowl-
edge, a program for the improvement of forage and the maintenance
of sustained high levels of sheep production can be undertaken.

In the following sections some suggestions are given for analyzing
winter range condition and instituting proper utilization standards,
stocking rates, and management practices. These are the tools by
means of which the objectives of increased forage yields and improved
sheep production can be reached.

JupGING RANGE CONDITION

The term “condition” is used to denote the general health and pro-
ductivity of the range. From extensive observations on winter ranges
throughout the region, and information obtained on specific sites within
the Desert Experimental Range, criteria or indicators were developed
to aid in judging the state of health or condition of the range. Among
the more important of these on winter ranges are: The status of soil,
composition of vegetation, vigor of plants, and the kind and amount
of seedlings and young plants.

Using these indicators it is possible to judge and classify the present
condition of most winter range areas. The following condition classes
illustrate how the various indicators are related to range condition.

1. Good condition—Soil stable with little or no evidence of accelerated
erosion; plants not pedestaled, good stand of palatable vegetation in
vigorous condition with production approaching a maximum consistent
with precipitation; seedlings of palatable species abundant enough to
maintain the current composition of the vegetation.

2. Fair condition—Soil showing signs of accelerated wind and water
erosion; undesirable species of low palatability present on some areas
and predominant on others; introduced annuals such as Russian-thistle,

54 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

halogeton, or cheatgrass scattered throughout the vegetation or on a
few localized spots; plant cover broken, and a number of dead and
partially dead plants of the palatable species such as Indian ricegrass,
winterfat, black sagebrush, and bud sagebrush present.

3. Poor condition—Soil erosion active; palatable native species often
pedestaled; plant cover thinned, numerous dead or partially dead
plants of palatable species, numerous introduced annuals such as
Russian-thistle, halogeton, mustards, cheatgrass, and foxtail bromes;
species of low palatability producing about 50 percent of the herbage.

4. Very poor condition—Soil erosion active; many of the smaller
drainages raw and eroding with very little vegetation; numerous annu-
als and species of low palatability producing most of the current herbage;
most of the palatable native vegetation severely injured or destroyed.

On the basis of extensive surveys made on the winter ranges of
the Intermountain region from 1932 to 1936, and observations made
on numerous enclosures scattered throughout Utah and Nevada, the
majority of these areas were classified as being in fair to poor condition,
with a considerable amount of range in very poor condition. Although
some of these areas have shown improvement during the last few
years under management, many of the ranges are still in fair to poor
condition, producing far below their maximum capacity.

The rate of recovery of the range varies according to subtype and
range condition. Some subtypes within the Desert Experimental
Range, which were classified in poor condition in 1935, improved
enough under moderate grazing to be classed as in good condition in
1947. Subtypes in which palatable perennial forage plants were pres-
ent in moderate numbers, even though low in vigor, recovered rapidly.
In 3 to 5 years, improvement in vigor of the better forage species was
readily apparent. Many young plants and seedlings of the choice
forage species were also present.

Recovery of areas in poor condition where palatable plants have
been severely injured or replaced by undesirable species is much slower,
but improvement is generally feasible if moderate grazing and carefully
planned management practices are adopted. The improvement of
ranges in very poor condition requires more than the reduction of
grazing intensities. It may be advisable to suspend grazing for vary-
ing periods of time, depending on the degree of deterioration that
exists. If reseeding of such areas can be done successfully, it will
undoubtedly speed recovery. Very little, however, is yet known about
methods and species suitable for seeding on these semiarid rangelands.
Much further research will be necessary before seeding of winter ranges
can be relied on to bring about widespread improvement.

UTILIZATION STANDARDS

Utilization records of winter grazing at the Desert Experimental
Range indicate that Indian ricegrass, black sagebrush, and winterfat,
all important key forage species, can remain productive and vigorous
on ranges in fair to good condition when 75, 60, and 55 percent,
respectively, of their current herbage is utilized. Under this moderate
degree of utilization 25, 40, and 45 percent, respectively, of the herb-
age is left ungrazed as protection to the plants and to insure sustained
production of the seed and of other important forage species.

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 90

The following minimum stubble heights and twig lengths are char-
acteristic of moderately grazed winter range. Indian ricegrass will
have an average of 2 to 3 inches of stubble remaining at the end of the
grazing season. Although all plants are usually grazed, a few of the
larger, more robust ones will usually have as much as 5 or 6 inches
of stubble. On galleta an average stubble height of 1 to 11% inches
will remain and 5 to 10 percent of its ground area, usually toward
the perimeter of stands, will be ungrazed. Black sagebrush will have
an average of 11% to 2! inches of current twig growth remaining and
in years when seed stalks are produced in abundance, 10 to 20 percent
of these will be ungrazed. On winterfat 11% to 2% inches of current
growth will remain and 10 to 15 percent of the plants will appear to
be ungrazed.

The percentages of utilization given in table 1 are useful utilization
guides in subtypes where the species listed make up a large part of the
plant cover or herbage production. These utilization guides should be
adhered to rather closely in order to maintain a moderate grazing
intensity. On range subtypes where winterfat, bud sagebrush, black
sagebrush, Indian ricegrass, and galleta do not occur, or on ranges
where they make up only a small proportion of the vegetation, it may
be necessary to select other key forage species on which to base utiliza-
tion guides. If scattered but choice forage species are to be maintained
in the plant cover, it may be necessary to use some of these as key
species and to reduce the grazing level enough to prevent grazing injury.

Where ranges are in a deteriorated condition, utilization percentages
must be adjusted to provide for range recovery. On ranges in poor
condition it may be necessary to leave more than 50 percent of the
herbage of the palatable species during 2 or 3 years while the vigor of
the plants is being restored. This will allow them to compete more
successfully with invading species or species of low palatability such
as Russian-thistle, shadscale, or small rabbitbrush. On ranges in very
poor condition it may be desirable to suspend grazing for as long as
2 years or to allow grazing only every other year. Within the experi-
mental range, a severely depleted winterfat subtype made satisfactory
improvement when grazed moderately in alternate years.

STOCKING RATES

Stocking rates for winter ranges should be in balance with the
capacity of grazing areas to produce forage. This is. necessary for
efficient production of sheep. To adjust stocking rates annually to
meet the wide fluctuations in forage production due to variations in
precipitation is obviously impracticable, because flocks are primarily
composed of breeding ewes which are grazed on other seasonal ranges
to round out the yearlong range livestock operation. A more work-
able procedure is to adjust the numbers of sheep so that they will be
in balance with the forage yield over a fairly long period of time.
The term “forage” is used to denote the amount of herbage which
can be grazed or used by sheep under moderate grazing without
injuring the range or impairing future production. The average stock-
ing rate should take into account differences in productive capacity
of different plant subtypes on the grazing area. Provision should also
be made for recurrent drought periods.

56 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

To provide for reasonable stability in winter grazing and to assure
an adequate forage supply year after year, a basic stocking rate
established at 75 percent of average forage production is recommended.
This is approximately the level of stocking maintained at the Desert
Experimental Range (fig. 23). On this basis, enough forage is pro-
vided for sheep in most years without need for further adjustment in
numbers or supplemental feeding. Only in years of drought or low
forage production would it be necessary to reduce sheep numbers or
to provide supplemental feed.

C€POUNDS PER ACRE )

bd
<
m
pt)
>
a)
m
N

FORAGE PRODUCTION
|
|

SXMYYLGAAAQAAMA
WN AQ NY

EI CW WCW
BID WWW I
saa

BR TW QQ ass

“44 ‘45

Figure 23.—Forage production of moderately grazed range areas at the Desert
Experimental Range, 1935-47. Utilization of the forage at 75 percent of the
average provided a margin of safety in all but 3 years when production was ex-
tremely low.

Forage forecasts based on the previous 12-month rainfall make it
possible for stockmen to foresee grazing seasons of short forage. It is
then possible to provide additional feed or arrange for the adjustment
of numbers before taking the sheep to winter ranges.

In establishing stocking rates the plant composition of the grazing
area and its present condition should be considered. Average grazing
capacities of seven subtypes in two condition classes, expressed in acres
required per sheep-month, are as follows:

Fair to good Poor

me condition condition

Subtype: (acres) (acres)
Shadiscalérass ss ee a oe eee ace ioe
Shadseale-wintertat-erass®= 2 Set So See 2.3 3..f
Black sagebrush-shadscale-grass______-_------------- 1.0 2.3
Winterfat-small rabbitbrush-grass_____________--_-_- 2 2.8
Littleleaf mountain-mahogany-black sagebrush-grass___ 2.8 4.3
Wanteriat se ee ee i Se See ee 1.0 2.4
Gray summer-cypress-Gardner saltbush-winterfat____-_- 1.9 2.6

fo ihe ny

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 07

These capacities were calculated by multiplying the air-dry herbage
yields obtained on the range areas in different conditions by the average
percentage utilization recorded on the moderately grazed experimental
range. The result was divided by 5.5 pounds, which is the approx-
imate range forage requirement including trampled herbage for a ewe
per day.

There is considerable variation in grazing capacity according to the
composition of a subtype and its condition. Subtypes where winterfat
and black sagebrush are abundant have the highest capacities and those
where shadscale is predominant, the lowest.

Subtypes in poor condition have a thinner cover of plants, usually
including few of the palatable species and a great many of the less
palatable. Because such range areas produce much less forage, grazing
capacity is only one-half to two-thirds that of comparable areas in fair
to good condition.

MANAGEMENT PRACTICES

After a program of moderate grazing has been installed on any winter
range area, it is of paramount importance to apply the best manage-
ment practices. The management practices outlined here will greatly
aid in obtaining uniform distribution of sheep, effective utilization of
forage, and efficient sheep production.

SUBDIVISION OF RANGE ALLOTMENTS

The subdivision of a large range allotment into smaller units that
are grazed at specified winter periods, as practiced at the Desert Ex-
perimental Range, has several advantages over random grazing of the
entire allotment. This is especially true when the periods of grazing
on units are rotated from year to year.

A new supply of a mixture of forage is assured when sheep are re-
moved from one unit and brought to a previously ungrazed one.
Another advantage is that portions of an allotment can be reserved for
use during shearing in portable corrals on the winter range.

General observations at the Desert Experimental Range indicate
that several forage species made superior gains in volume on units
grazed during the early and middle winter periods but not in the late
winter. These species included bud sagebrush, Indian ricegrass, hop-
sage, and squirreltail. All begin their growth in the early spring, which
coincides with the late winter grazing period, and grazing them at that
time reduced their vigor considerably. To permit maximum production
of these species it may be necessary to eliminate the late winter grazing
on a portion of the allotments each year. This can be accomplished
by rotating the use of three or more units so that some of the units are
not grazed in the late winter period for one or two years in succession.

HERDING

The following herding practices are recommended on the basis of
experience at the experimental range: (1) Allow sheep to spread out and
graze quietly and keep trailing in groups to a minimum; (2) plan routes

58 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

of grazing to give sheep a variety of forage but at the same time avoid
prolonged use of any particular area; (3) bed sheep in a different location
each night, preferably one that is selected beforehand so that the ani-
mals can reach it after the day’s grazing; and (4) avoid overuse of dogs,
since they encourage close herding.

It may be necessary to corral herds at various times during the
winter for such purposes as making counts, marking, shearing face wool,
or segregating sheep. This can be done in portable corrals constructed
of panels or lath snow fences and steel posts. Such corrals should be
placed on hard or somewhat gravelly ground to avoid excessive damage
from trampling...

Shearing in portable corrals before the sheep leave the winter ranges
is becoming a common practice. One or two flocks are shorn at a corral
location, usually near water. The sheep are removed from the shearing
area immediately after they are shorn and placed on ranges where forage
is available. The corral is then moved to a new location for the next
herd. Adjacent range areas are used for grazing only briefly and there-
fore are not given as severe use as areas around permanent shearing
corrals where several flocks are shorn year after year. It may be highly
desirable to place the shearing corrals in a new location each year to
prevent injury to the range.

WATERING

Adequate watering of sheep is important in keeping them in good
condition. Studies at the Desert Experimental Range (8) indicate that
sheep require about 0.7 gallon each per day on winter range. In warm
weather they may need 1.5 gallons and if forage is dry or composed
mostly of shadscale or Gardner saltbush as much as 2 gallons per day.

Sheep should receive a supply of fresh water every day. During the
middle part of most winters they can obtain the necessary water from
snow, provided it is uniform and not too deep. Relying entirely on
snow for water throughout most winters, however, places undue hard-
ships on the sheep and on the range. Even in the middle winter there
may be too little snow, or snows may be crusted and hard to utilize for
water. In early and late winter when snow is scarce, animals must be
trailed back and forth from grazing areas to higher elevations for snow
or to reservoirs where water is available.

A much better practice is to truck the water to the sheep, preferably
every day when snow is not uniformly and readily available. Water
may be supplied in portable troughs, which should be placed so that
sheep movements can be directed across the desired range areas.
Enough troughs should be provided to avoid crowding. A spacing of
40 to 50 feet between troughs is recommended.

SUMMARY

Winter ranges in the Intermountain region furnish forage for ap-
proximately 4 to 5 million sheep for a period of 4 to 6 months. These
ranges are extensive, comprising in all about 65 million acres. They
are characterized by low precipitation and scant vegetation. This
naturally sparse plant cover has been greatly depleted by grazing over-

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 59

use from the turn of the century up to recent years. The depletion
has been further intensified by accelerated wind and water erosion and
by droughts. To bring about recovery and insure maintenance of
these important ranges will require knowledge of their grazing potentials
and application of improved management practices based on this
knowledge.

The Desert Experimental Range was established by the Forest
Service in 1933 for the study and solution of problems existing on such
rangelands. Fifty-five thousand acres of typical winter range in west-
ern Millard County, Utah, were selected and fenced into experimental
pastures and allotments. Studies were conducted on these areas and
on neighboring open range from 1935 to 1947 to determine: (1) The
utilization of forage species by sheep; (2) the influence of precipitation
on herbage production; (8) the effects of grazing intensity on forage
yields; and (4) the effects of grazing intensity on sheep production.

Detailed data on herbage production, plant density, and utilization
of vegetation as well as weight changes of sheep were obtained from the
experimental pastures, which were grazed at light, moderate, and heavy
intensities. Additional data on herbage production, forage utilization,
and several phases of sheep production were obtained from two range
allotments, one heavily and one moderately grazed, on which two herds
of sheep were alternately wintered.

The plant types and subtypes characteristic of the winter range are
well represented within the experimental range. Seven major subtypes
cover more than 94 percent of the area, with pinyon and juniper
forming an open overstory on about one-fifth of the total. Several
hundred plant species are found on both the experimental range and
the general winter range but only about 30 are abundant and palatable
enough to be classed as important forage species.

Within the experimental pastures, located on valley alluvial fans,
vegetation consists chiefly of shadscale-winterfat-grass subtypes. These
are among the most extensive plant subtypes on the winter range but
they are not the most productive of forage. During the period of
study, five species—winterfat, shadscale, Indian ricegrass, galleta, and
sand dropseed—produced 80 percent of the herbage and furnished 88
percent of the forage in moderately grazed pastures. Winterfat alone
contributed 35 percent of the forage, almost twice as much as any
other plant.

Utilization of forage plants was influenced primarily by their level
of palatability, but other factors such as relative abundance, stage of
maturity, and weather conditions also had considerable influence on
the kind of forage eaten. Winterfat, Indian ricegrass, sand dropseed,
and galleta were utilized more heavily in pastures where they were
relatively scarce than where they made up larger proportions of the
herbage.

Total herbage production of the subtypes within the pasture area,
as estimated in October, was closely associated with precipitation
received during the preceding 12 months. Average 12-month precipi-
tation between October 1934 and October 1947 was 6.69 inches.
Average herbage production was only 219 pounds per acre with a
maximum of 468 pounds in October 1947 following 11.10 inches of
precipitation, and a minimum of 75 pounds in 1943 after 2 years of
drought.

60 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

Herbage production was found to increase approximately 46 pounds
an acre with each additional inch of precipitation. This close relation
has provided a basis for forecasting forage at the experimental range
from precipitation records up to October of each year. Such forecasts
would enable sheep operators to provide supplemental feed or other-
wise make adjustments for indicated short forage before taking their
herds to the winter range.

In the pastures the trend of total herbage production during the
period of study was upward under all three intensities of grazing, the
increases being respectively 54, 46, and 34 percent for light, moderate,
and heavy grazing. Winterfat, the most productive and palatable
shrub in the pasture area, showed trend increases of 239, 321, and
33 percent under light, moderate, and heavy grazing. Shadscale,
more abundant but lower in palatability, increased slightly more under
moderate grazing and much more under light grazing than under
heavy grazing. Galleta and sand dropseed declined slightly under all
intensities of grazing primarily because of infrequent favorable summer
rainfall. Indian ricegrass, bud sagebrush, and globemallow, which
made up small amounts of the plant cover, did not show any consistent
response to the differential grazing treatments.

Other plant subtypes showed changes in vegetal composition under
two intensities of grazing on large range areas inside and outside of
the experimental range. In a shadscale-Indian ricegrass subtype,
yields of the palatable Indian ricegrass increased from 30 percent of
the total in 1934 to more than 40 percent in 1947 under moderate
grazing. Under heavy grazing production dropped to 15 percent of
the total by 1947.

The valuable black sagebrush increased remarkably in volume under
moderate grazing on a depleted subtype which originally produced
primarily winterfat, rabbitbrush, and only small amounts of grass and
black sagebrush. This species produced only 7 percent of the herbage
in 1934 but by 1947 made up more than 40 percent of the total,
because of increases in vigor and establishment and growth of seedlings.
On the adjacent part of the subtype, where heavy grazing was con-
tinued, rabbitbrush remained the dominant species.

Low-value annuals and undesirable shrub species were generally
supplanted by more palatable species when grazing pressure was re-
duced or suspended. As an example, an ungrazed enclosure was
erected in 1937 on an area where Russian-thistle produced about 60
percent of the vegetation. Three years later this species was almost
completely supplanted by winterfat and Indian ricegrass within the
enclosure. By 1947 Russian-thistle produced only 2 percent of the
herbage in the enclosure. On the neighboring heavily grazed range,
Russian-thistle production was 402 pounds an acre or 54 percent of
the total herbage.

Ewes on moderately grazed range maintained body weights of 4 to
18 pounds more than those on heavily grazed range. They also pro-
ducedabout a pound more wool and 11 percent more lambs. Costs
of feeding sheep in poor condition and death losses were greatly re-
duced. Income from herds wintered at moderate grazing levels and
under good management practices averaged $3.46 per ewe as compared
to $1.69 from herds on heavily grazed range.

‘i

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 61

On the basis of findings at the experimental range, condition of
winter range areas has been grouped into four broad classes which can
be identified by relatively few indicators. These classes are: Good,
fair, poor, and-very poor. Knowledge of the extent of these condition
classes on a range is essential to the application of proper utilization
standards and stocking rates.

Records obtained at the experimental range indicate that approxi-
mately the following proportion of the herbage of major forage species
can be eaten during the winter period without impairing their con-
tinued productivity: For Indian ricegrass 75 percent, black sagebrush
60 percent, winterfat 55 percent, and galleta about 45 percent.

To provide for reasonable stability in winter grazing and to assure
an adequate forage supply in most years, a basic stocking rate that
will utilize 75 percent of average forage production is recommended.
Grazing capacities of range subtypes in fair to good condition are 144
to 244 times greater than for those in poor condition. On ranges in
fair to good condition 1 to 3.5 acres are required per sheep per month,
whereas on those in poor condition 2.3 to 5.7 acres are required.

Studies at the Desert Experimental Range indicate that certain
management practices are of benefit to both ranges and sheep. These
include subdivision of large grazing allotments so that grazing use
may be rotated from year to year, use of open herding and one-night
bedgrounds, leaving the range early to avoid grazing during the late
winter period when many of the major forage plants begin to grow,
and providing water for sheep each day.

DITERATURE CITED

(1) Barnss, W.C.

1926. THE STORY OF THE RANGE. U.S. Senate, 69th Cong., Ist sess. (Re-
printed from Part 6 of the Hearings before a subcommittee of the
Committee of Public Lands and Surveys.) 60 pp., illus.

(2) BRoapDBENT, D. A., BLancH, G. T., anp THomas, W. P.

1946. AN ECONOMIC STUDY OF SHEEP PRODUCTION IN SOUTHWESTERN UTAH.

Utah Agr. Expt. Sta. Bul. 325, 65 pp.., illus.
(3) Cook, C. W., ann Harris, L. E.

1950. THE NUTRITIVE CONTENT OF THE GRAZING SHEEP’S DIET ON SUMMER AND
wee RANGES OF UTAH. Utah Agr. Expt. Sta. Bul. 342, 66 pp.,
illus.

(4) Crappock, G. W., AND Fors.inG, C. L.

1938. THE INFLUENCE OF CLIMATE AND GRAZING ON SPRING-FALL SHEEP RANGE

IN SOUTHERN IDAHO. U.S. Dept. Agr. Tech. Bul. 600, 42 pp., illus.
(5) Espiin, A. C.

1932. EFFECT OF FEED, WATER AND SHELTER UPON FLEECES OF UTAH EWES.

Utah Agr. Expt. Sta. Bul. 240, 26 pp., illus.
GREAVES, J. E., AND STopparT, L. A.

1937. A STUDY OF UTAH’S WINTER RANGE; COMPOSITION OF FORAGE PLANTS
ae USE OF SUPPLEMENTS. Utah Agr. Expt. Sta. Bul. 277, 48 pp.,
illus.

(7) HocumutaH, H. R., FRanKuin, E. R., anpD Cuawson, Marion.

1942. SHEEP MIGRATION IN THE INTERMOUNTAIN REGION. U.S. Dept. Agr.

Cir. 624, 70 pp., illus.
(8) HutcHines, SELAR S.

1946. DRIVE THE WATER TO THE SHEEP. Natl. Wool Grower. 36: 10-11, 48,
illus.

(9) Kearney, T. H., Bricas, L. J., SHantz, H. L., McLane, J. W., ano Piz-

MEISEL, R. L.

1914. INDICATOR SIGNIFICANCE OF VEGETATION IN TOOELE VALLEY, UTAH.
Jour. Agr. Res. 1: 365-417, illus.

(6)

62 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE

(10) Netson, E. W.
1934. THE INFLUENCE OF PRECIPITATION AND GRAZING UPON BLACK GRAMA
GRASS RANGE. U.S. Dept. Agr. Tech. Bul. 409, 32 pp.., illus.
(11) PEcHANEC, J. F., AND PickForpD, G. D.
1937. A COMPARISON OF SOME METHODS USED IN DETERMINING PERCENTAGE
UTILIZATION OF RANGE GRASSES. Jour. Agr. Res. 54: 753-765.

(12) AND Pickrorp, G. D.
1937. A WEIGHT ESTIMATE METHOD FOR DETERMINATION OF RANGE OR PASTURE
PRODUCTION. Amer. Soc. Agron. Jour. 29: 894-904.
(13) AND STEWART, GEORGE.

1949. GRAZING SPRING-FALL SHEEP RANGES OF SOUTHERN IDAHO. U.S. Dept.
Agr. Cir. 808, 34 pp., illus.
(14) Pinerey, H. B.
1945. SHEEP RANCHING IN SOUTHEASTERN NEW MEXICO. N. Mex. Col. Agr.
Bul. 325, 64 pp., illus.
(15) Prick, RayMonp, ParRKER, K. W., AND HULL, A. C., JR.
1948. THE FOUNDATION OF THE RANGE. U. 8. Dept. Agr. Yearbook, pp.
553-556.
(16) SHantz. H. L.

1925. PLANT COMMUNITIES IN UTAH AND NEVADA. In Tidestrom, I., Flora
of Utah and Nevada. U.S. Natl. Mus. Contrib., U. S. Natl. Her-
barium, Vol. 25: 15-23.

AND PIEMEISEL, R. L.
1940. TYPES OF VEGETATION IN ESCALANTE VALLEY, UTAH, AS INDICATORS OF
SOIL CONDITION. U.S. Dept. Agr. Tech. Bul. 713, 46 pp.., illus.
(18) SNEDECcOR, G. W.
1946. STATISTICAL METHODS. Ed. 4, 485 pp., illus. Ames, Iowa.
(19) Stewart, G., Corram, W. P., anp Hutcuines, 8.8

1940. INFLUENCE OF UNRESTRICTED GRAZING ON NORTHERN SALT DESERT
PLANT ASSOCIATIONS IN WESTERN UTAH. Jour. Agr. Res. 60: 289-
316, illus.

AND HuTcHINGS, S. S.
1936. THE POINT-OBSERVATION-PLOT (SQUARE-FOOT DENSITY) METHOD OF VEGE-
TATION SURVEY. Amer. Soc. Agron. Jour. 28: 714—722, illus.
(21) Unirep Statres Forest SERVICE
1936. THE WESTERN RANGE. U.S. 74th Cong., 2d sess., S. Doc. 199. 620
pp., illus.
(22) Witson, J. F.
1931. INFLUENCE OF THE PLANE OF NUTRITION UPON VARIOUS FACTORS RE-
LATED TO WOOL PRODUCTION. Natl. Wool Grower 21: 23-28, illus.
(23) WooxFoLk, E. J.
1949. STOCKING NORTHERN GREAT PLAINS SHEEP RANGE FOR SUSTAINED MAXI-
MUM PRODUCTION. U.S. Dept. Agr. Cir. 804, 39 pp.., illus.
(24) Wooton, E. O.
1932. THE PUBLIC DOMAIN OF NEVADA AND FACTORS AFFECTING ITS USE. U.S.
Dept. Agr. Tech. Bul. 301, 52 pp., illus.

(17)

(20)

COMMON AND BOTANICAL NAMES OF SPECIES

MENTIONED
SHRUBS

Creosotepushs- Coville a2 ee aos Larrea tridentata
HponedravNevadacs a: attest oad ee oe Ephedra nevadensis
Crease WOOd wDlac esas a a Sarcobatus vermiculatus
PL OSHS CVS Ye 2 2 ae Reed oe Some tat Grayia spinosa
Forsebrushislittleledtis 20 as aie ae Tetradymia glabrata
Mires cnui ters 24 Os ae ee eee Prosopis spp.
Mountain-mahogany, littleleaf_________- Cercocarpus intricatus
Pickleweed________-_- ae ee a eens Allenrolfea occidentalis

Rabbitbrush, rubbers 2° ss ae Chrysothamnus nauseosus

Mewk. *,

INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 63

SHRUBsS—Continued

Rabbitorush, smalls ss Chrysothamnus stenophyllus
SAC ORUSM DIO an toe Pe EN Artemisia tridentata
Sevebrush Diack! 116 8 ee se A. nova

BASE DRUGS UCM Mere Ge ek ee ee A. spinescens
Saacbrush, irmmged = = 3 tc ee A. frigida
SalGoush fOUrWING es re Atriplex canescens
Sal cloucn Gardner ee A. gardneri
DalGousm may 909 te A corrugata
Saltbusmshadscale oo. yf SG a A. confertifolia
DCC CeCe ee oe rs ase Suaeda spp.
Smakeweed, DrOOM= =i5 4 90 ee Gutierrezia sarothrae
WM IMIMer=Cy Press: OTaY, 23 22242 22 ee Kochia vestita
Winterfat, common (whitesage)________- Eurotia lanata
CCA SoS oe ee Yucca spp.

GRASSES AND GRASSLIKE PLANTS

ipromecheaterass = 52 ee Bromus tectorum
BROMIGs OXbAT = seer Oe Sr er B. rubens
Dropsecde san. 2 2640 ee Sporobolus cryptandrus
Dropseeds spike. 22 ee S. contractus
Galletaes Sita ee er Hilaria jamesit
uit, We 2 8s ee Bouteloua gracilis
Needle2and=thread 2.9 Stipa comata
Needleorass, Mormon ©2222 22 re S. arida
iNicesrass, tidiane << 88 od sss. Oryzopsis hymenoides
Sacavonms aikalis 2 ese en Sporobolus airoides
DalGerass 2a ee Distichlis spp.
Souirreltail bettlebrush 22222 222 = = Sitanion hystrix
Wheatgrass, bearded bluebunch_________ Agropyron spicatum
VWalciayjee owing iP A ee Se Elymus salina
Fors
Globemallow, gooseberryleaf___.._____- Sphaeralcea grossulartaefolia
IMO MeUOMe Sa en a ee Halogeton glomeratus
Pepperweed _ ____- Be eee Lepidium scopulorum
Russian-thistle, tumbling === 92... Salsola kali tenurfolia
TREES
dumiper Utahes so rot Ses ee Be Juniperus osteosperma
Binyon. cmeleleadi: 22.2 ee Pinus monophylla

W U.S. GOVERNMENT PRINTING OFFICE: 1953—255435

For sale by the Superintendent of Documents U:S.Government Printing Office
Washington 25, D.C. - Price 20 cents

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