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. 
