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-oft' 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 
„-> AREA-A<^ STREAM FLOW 
EROSION C 
PRECIPlTATlONl 
*•> AREA-B<! STREAM TLOW H 
EROSION LZ 
(PRECIPITATION ■ 
STREAM FLOW (S3 
EROSION 
□ 
UNGRAZED 
UNGRAZED 
UNGRAZED 
g. I" PRECIPITATION ■ 
cCarea-b^ stream flow £2 
i erosion d 
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 tbe 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 tbe 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. 
