22 



BULLETIN 1170, U. S. DEPARTMENT OF AGRICULTURE. 



grama grass and the bunches of needle grass. The larger mats and 

 bunches have broken up since 1916. The dry seasons have no doubt 

 been of greater influence as a direct cause of this than has the graz- 

 ing in the case of blue grama. Western needle grass has been greatly 

 reduced in extent in the quadrat in the 30-acre pasture. This has 

 no doubt been largely because of the intense grazing, since the reduc- 

 tion is twice as much as in the quadrat in the 100-acre pasture. This 

 fact is further confirmed by observation and by the clipped quadrats. 

 Western needle grass does not withstand severe grazing as well as 



Fig. 8. — Square-meter quadrat in the 30-acre pasture, showing the relationship of Bou- 

 teloua and Stipa. Charted near the close of the grazing season in 1916. Bouteloua 

 gracilis is indicated by B and Stipa comata by S. 



blue grama. It is a shorter lived perennial and is more dependent 

 upon reseeding. Western needle grass is the species that is bene- 

 fited most by the system of deferred and rotation grazing. € 



ISOLATION TRANSECTS. 



Areas that are now known as " isolation transects " 18 were set 

 aside in the 100-acre and the 30-acre pastures in 1915. A similar area 



18 Dr. H. L. Shantz suggested these areas when he visited the station in 1915. Their 

 designation as isolation transect? was suggested by Dr. F. E. Clements when he visited 

 the station in 1917. 



