6 BULLETIN 122*7,, U. S. DEPARTMENT OF AGRICULTURE 



Changes in the vegetation were measured quantitatively by means 

 of five permanent quadrats, two in each of the fenced areas and 

 one outside. These were charted every year at the end of the grow- 

 ing season and one quadrat in each of the three plots clipped at that 

 time and the crop of grass weighed by species. The results thus 

 measured were striking, and show in a very marked manner not only 

 the differential effects of rodent and cattle grazing, but the responses 

 of each of the grasses to such grazing (Pis. V and VI). 



In 1918, when the first three quadrats were installed, the sand drop- 

 seed {Sporobolus cryptcmdrus) was almost extinct, appearing in 

 only one of them. This was due largely to its great palatability, 

 both cattle and prairie dogs seeking it and grazing it to the ground 

 at all times. The established plants were holding on in some measure 

 by producing a crop of short leaves close to the ground in the man- 

 ner characteristic of the blue grama, which enabled them to survive 

 in spite of close grazing by cattle. But plants near the prairie-dog 

 burrows were utterly destroyed, for the rodents had grazed the 

 grass down to the tops of the roots, rarely leaving so much as a bud 

 to reestablish the plant. 



The chief result noted after the growing season of 1918 was the 

 first appearance of seeding plants of dropseed in the totally pro- 

 tected plot. Such plants occurred in the prairie-dog inclosure also 

 but only at some distance from the group of burrows. Very few of 

 these plants were seedlings ; in fact, nearly all may be said to have 

 been established plants, permitted by protection to produce their first 

 real crop of seed. 



As a result of this crop, the fall of 1919 showed dropseed plants 

 everywhere on the whole area, and from that time on this grass has 

 been of almost equal importance with wheat grass on and around the 

 plots. This was due to the great amount of seed produced in the 

 protected plots scattering over the entire area and reestablishing 

 plants where grazed out. The plants were grazed down by cattle 

 outside the plots, however, and in the rodent inclosure, were grazed 

 down and gradually killed so that while these plots showed at times 

 nearly as many plants per square meter as in the protected area, 

 clipping in fall showed little forage left. 



In the spring of 1918 the wheat grass {Agropyron smithii) 

 plainly showed the effects of overgrazing. This grass does not 

 produce short leaves close to the ground as does blue grama (and 

 also dropseed when forced to it), but sends up leafy stems which, 

 when grazed closely, have no photosynthetic surfaces left. Such 

 plants must draw upon stored food-material to send up short shoots 

 which may escape and permit food supplies to be in some measure 

 replenished. The habit of the wheat grass of spreading by rhizomes, 

 however, is distinctly in its favor. Seeding is always a precarious 

 means of reproduction under grazing conditions, while spreading 

 by rhizomes' permits pooling of the food produced by the few 

 shoots which escape for the use of all shoots arising from the 

 rhizome. The tougher texture and scabrous leaves of the wheat 

 grass make it less palatable than either grama or dropseed, hence 

 a few shoots at least are apt to remain untouched. When heavily 

 grazed for some years, however, the rhizomes become starved, and 



