DAMAGE TO EAN"GE GRASSES BY THE ZUNI PBAIRIE DOG 5 



Grand Canyon post office. The place selected is in the " wash," 

 which is best described as a water-made park in the yellow-pine 

 forest which forms a broad belt along the south rim of the Grand 

 Canyon at this point. The characteristic vegetation of the area 

 (Pis. I and II) is the western wheat grass (Agropyron- smithii) 

 (PI. Ill), sparsely dotted with bushes of the true sagebrush (Arte- 

 misia tridentata) . The wheat grass is predominant, but where some 

 protection permits it to produce seed the sand dropseed (Sjjoroholus 

 cryptandrus) is of nearly equal importance. Blue grama (Bouteloua 

 gracilis) (PI. IV) is present also, but thus far has been of minor 

 importance. Several other grasses, such as the June grass (Koeleria 

 cristata) , occur but are rare and of little economic importance. 



Two plots were measured off on April 14, 1918, each approximately 

 three- fourths of an acre in extent (132 by 247.5 feet). One quadrat 

 was staked out and charted in each of the plots and another outside. 

 The plots were fenced on May 27, 1918. To exclude stock, four 

 strands of barbed wire were utilized. For the prairie-dog inclosure 

 a strip of 1-inch-mesh galvanized wire 3 feet wide was used in addi- 

 tion, the lower 6 inches being buried in the ground, leaving 2 x /2 feet 

 above the surface as a barrier to the rodents. 



Careful counts indicated the infestation of prairie dogs in this 

 region to be about 25 individuals to the acre. A like proportion, or 

 18 or 20 animals, were found to have been fenced in the inclosure. 

 Prairie dogs in the total-protection area and outside the inclosures 

 were eliminated by thorough poisoning. Some difficulty was ex- 

 perienced in retaining the rodents where needed and in excluding 

 them from " protected " areas, and this constituted a source of error 

 in the experiments, but these, tending to minimize rather than ex- 

 aggerate the results, show the damage as less extreme on the areas 

 than probably would otherwise have been the case. 



Two quadrats, one in each fenced plot, were added to the first 

 three on May 19, 1919, by Doctor Vorhies, who charted the quadrats 

 at that time. These, and the one outside, were clipped at the end 

 of the growing season that year and each year thereafter, the results 

 being shown in Table 1 on page 8. 



PROGRESS OF THE EXPERIMENT. 



When the inclosures were first fenced on May 27, 1918, the grasses, 

 under the combined grazing of stock and rodents, had been cropped 

 off short throughout the region, so short, in fact, as to make identi- 

 fication of the different species difficult. By November 13, 191S, 

 however, certain noteworthy changes had taken place. The grasses 

 under total protection were knee high. The forage in the rodent 

 inclosure was in good condition also, though plainly showing the 

 effects of rodent work. Around one series of burrows within this 

 inclosure a circular area about 40 feet in diameter had been al- 

 most entirely grazed off by the rodents. Fifteen or twenty feet 

 seemed to be about the average radius of intensive prairie-dog dam- 

 age, though it was evident that some rodent grazing had been done 

 over the entire area. Outside the fences, where stock had been graz- 

 ing freely, the grass was cropped short, resembling its condition when 

 the fences were first installed. 



