RANGE PRESERVATION AND EROSION CONTROL. 



25 



the selected areas, strikingly significant results as to the effects of 

 grazing and nongrazing were obtained. 1 



On July 21, 1915, when both areas had been protected from graz- 

 ing since August, 1914, a heavy rainstorm occurred in which area 

 B received approximately twice as much precipitation as area A : 

 but only about one-twelfth as much run-off and one-ninth as much 

 erosion was recorded from area B as from area A. On August 5, 

 1916, area B was grazed closely by sheep, area' A being at that time 

 ungrazed. Late in the day of August 5, a rainstorm occurred in 

 which both of the. selected areas received an average of 0.25 of an 

 inch of rain. Practically the same amount of run-off was recorded 





( PRECIPITATION WBM 



» 







tr, AREA-A< 



STREAM FLOW K\\\ v 



A\\\ 



V\\\1 



UMr,RA7En 



o- 



™ 





o* C 



/.F>. 







I 





^ ER05ION 1 i 













,1 



?J 



HUN 



>« EDS 









1 



5 



^ OREA-B < 



f PRECIPITATION^^B 







STREAM TLOW H 

 * EROSION 1 1 





UNGRAZED 



{PRECIPITATION I 

 STREAM FLOW k\\1 

 E-ROSION EZ1 



UNGRAZED 



jg. I" PRECIPITATION ■ 



«£ AREA-B < STREAM FLOW ES3 

 I EROSION. □ 



Fig. 6. — Relation of grazing and nongrazing to erosion and run-off. 



from the two areas, and the erosion from area B was one-half that 

 from area A, as shown in figure 6. 



It will be noted, then, that the ratios of precipitation, run-off, and 

 erosion on area B as compared with area A were changed from 2/1, 

 1/12, 1/8, respectively, to 1/1, 1/1, 1/2, respectively, as a result of 

 grazing area B and not area A. Since grazing was the only factor 

 changed as compared with all previous records, it appears safe to 



1 The grazing of the areas was carried out as follows : Both pastures were grazed mod- 

 erately close by sheep at practically the same time in the season in 1914-1916, inclusive. 



The prescribed time for cropping the areas is when the forage is sufficiently developed 

 to afford good grazing, a time which corresponds fairly closely to the grazing of the 

 unprotected adjacent range. In case the ground is sufficiently wet to injure the vegeta- 

 tion seriously by trampling, or to cause harmful packing of the soil, grazing is deferred 

 until a later date when soil conditions are normal. A band of sheep of the average size — 

 about 2,500' head of ewes and lambs — is grazed on the areas. The sheep are allowed to 

 graze at will, being worked over the pasture only to the extent of assuring uniform crop- 

 ping. The vegetation is grazed closely but by no means destructively, the grazing corre- 

 sponding in this particular to that on the adjoining range. 



