26 CIRCULAR 804, U. S. DEPARTMENT OF AGRICULTURE 



larger on the heavily stocked pasture than elsewhere in 1942, after 6 

 years of sheep grazing, heavy stocking evidently had such effects as 

 killing the small plants that survived the drought or preventing the 

 establishment of new plants following the drought. The important 

 point is that threadleaf sedge was only about half as abundant on the 

 small pasture after 6 years of heavy stocking as on other pastures 

 stocked more lightly. On the area protected after early 1938, the 

 plants were intermediate in size between those on heavily and con- 

 servatively stocked range but were very sparse. 



NEEDLE-AND-THREAD 



Needle-and-thread grass, another important clump-forming species 

 and one of the most sensitive to grazing, was by 1942 very sparse in 

 the heavily stocked pasture. Plants on the sample plots averaged 

 only about one-fourth and one-half as numerous, respectively, as on 

 the conservatively and lightly stocked pastures (table 6). Besides 

 being much less numerous, needle-and-thread clumps were less than 

 half as iarge on the heavily stocked pasture as in the lightly stocked 

 and unstocked areas (table 7). The plants were somewhat smaller 

 on the conservatively stocked than on the protected and lightly 

 grazed areas but still considerably larger than under heavy stocking. 

 Heavy grazing and trampling retarded the recovery from drought 

 of surviving needle-and-thread plants and limited the establishment 

 of new plants from seed. These findings strengthen the plot-den- 

 sity data and help explain the sparser stand of vegetation on the 

 heavily stocked pasture. 



BLUESTEM WHEATGRASS 



In 1942 there was nearly twice as many stems of bluestem per plot 

 on the lightly stocked range and more than twice as many on areas 

 protected since 1938 as on the heavily stocked. There was little differ- 

 ence in the stand of bluestem on conservatively and heavily stocked 

 areas. Because of its single-stemmed growth habit, bluestem does 

 not form a sod but by means of underground rootstocks increases 

 rapidly in the stand when relieved from grazing. The large number of 

 stems per plot on the lightly stocked and protected areas undoubtedly 

 helps to account for the greater total density on these areas in 1942. 



ALL ANNUAL SPECIES 



Low-value annual species such as woolly Indianwheat and sixweeks 

 fescue were five and two times more abundant in the heavily stocked 

 pasture by 1942 than in the other two grazed pastures, respectively 

 (table 6). By retarding the recovery of palatable perennial species, 

 heavy stocking permitted an increase in annual species (fig. 10) which 

 at best are only temporary and provide a limited amount of forage. 



Effects on Height Growth of Blue Grama and Bluestem 



Wheatgrass 



Height growth of blue grama leaves and seedstalks was greater in 

 1942 on the conservatively stocked pasture by 22 and 3 percent, 

 respectively, than on the heavily stocked pasture (table 8). On the 

 protected areas the leaves and seedstalks were 55 and 10 percent taller 

 than on areas stocked heavily during 6 previous years. The propor- 



