GEAZING RANGES IjST 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. 



Table II. — Average summer production of forage in certain parts of the Santa 

 Rita Range Reserve, Aris., as computed from the quadrat measurements made 

 in 1912 to 1914, inclusive. 





Number 

 of col- 

 lections 

 used. 



Total 

 herbage. 



All grasses. 



Perennial grasses. 



All perennial 

 plants. 



Name of plant 

 association. 



Weight 

 per 

 acre 

 pro- 

 duced. 



Weight 

 per 

 acre. 



Part of 

 total. 



Weight 

 per 

 acre. 



Part of 

 total. 



Weight 

 per 

 acre. 



Part <if 

 total. 



Needle grass 



U 



23 



Pounds. 

 1,243 

 1,045 



Pounds. 



1,067 



972 



Per cent. 

 86 

 93 



Pounds. 

 1,010 



864 



Per cent. 

 81 

 S3 



Pounds. 



1,082 



932 



Per cent. 

 87 



Crowfoot grama 



89 



Table II 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, i. 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 Avould 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 



