GRAZING RANGES IN SOUTHERN ARIZONA. 19 
Assuming these conclusions to be correct we find in our results 
from quadrat collections data of sufficient accuracy for making esti- 
mates of the normal productivity and, therefore, the normal carrying 
capacity of ranges of this character. With these as a basis, still fur- 
ther generalizations relative to other forage-plant associations are 
also possible, since they may be derived from the ratios of produc- 
tivity of the different areas as shown by the collections. 
Taste II.—Average summer production of forage in certain parts of the Santa 
Rita Range Reserve, Ariz., as computed from the quadrat measurements made 
in 1912 to 1914, inclusive. 
Total : All perennial 
herbage. All grasses. Perennial grasses. plants. 
Number 
Name of plant ofcol- | weicht 
association. lections eS ae Toto ak 
used. ts x Aas Part of | oan Part of | “V cet Part of 
pro- Barey total. aa. total. Gre total. 
duce 
Pounds. | Pounds. | Per cent.| Pounds. | Per cent.| Pounds. | Per Ces 
Needle grass.......--- 11 1, 243 1,067 86 1,010 81 1,082 8 
Crowfoot grama...... 23 1,045 972 93 ” 864 83 939 89 
Table Il brings out an approximation to the relative produc- 
tivity of the crowfoot-grama and needle-grass associations for three 
years, the former producing about 1,000 pounds of herbage per acre 
and the latter about 20 per cent more. This comparison may be a little 
unfair to the needle-grass association, since most of that area has 
been subjected to grazing, while the other has not. Another condi- 
tion making against the accuracy of the comparison lies in the loca- 
tions where collections were made. The 11 collections in the needle- 
grass association were mostly made near the lower edge of the area, 
where the effects due to the presence of stock are most noticeable. Of 
the 23 collections in the crowfoot-grama area, 18 are from the better 
parts of the area and only 3 are near its poorer boundaries. Thus 
the productivity of the needle-grass area as given is probably slightly 
below the average and that of the crowfoot grama is almost certainly 
a little above the average for its total area. They show nearly 
similar compositions, 1. e., approximately 90 per cent of grasses, about 
80 per cent of perennial grasses, and close to 90 per cent of peren- 
nials of all kinds. 
Spring collections made in these areas have added very little to 
their total annual productions, though this would certainly be in fa- 
vor of the needle-grass area, where no such collections have been 
made recently. Only seven spring collections have been made in the 
crowfoot-grama area, and they show a spring growth varying from 
12 to 682 pounds per acre, the average of the seven being 178 pounds. 
Five of these collections, which were made after the summer growth 
began, show that the spring growth then constituted but a small 
part (from less than 5 per cent to about 33 per cent—77 per cent in 
