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 
