GRAZING RANGES IN SOUTHERN ARIZONA. 39 
of southern Arizona and possibly to an even larger area. Records 
of four kinds have been obtained. 
(1) Collections of everything growing upon small measured areas 
(quadrats) have been made for a number of years in representative 
parts of the range reserve, and from the weights of the dry material 
collected the total productivity in terms of pounds of forage per 
acre has been calculated. ‘These records extend over a period of nine 
years. From each year’s collections an average for the year has been 
obtained. From these yearly averages something is learned of the rate 
of improvement of the pasture, and from an average of all records 
is obtained an approximate value of the average total annual pro- 
ductivity, which is about 1,160 pounds per acre. This figure is 
obtained by a method that denudes the ground. Stock always get 
less than this amount. 
(2) Records of hay cutting on part of the reserve have been 
obtained for the past five years on areas varying from 1 to 114 acres. 
The total area for all seasons from which measurements were 
obtained was 4924 acres. The average amount of hay obtained is 
640 pounds per acre. Three areas, each about an acre in extent, 
which had the hay cut off for four years in succession, lost in produc- 
tivity from one-half to three-fourths of what they produced at the 
start, as the result of continued cutting. The average production 
of hay on this land is about 70 per cent of the productivity shown 
by the quadrat collections made on and beside the areas cut over; 
hence, it 1s argued that stocking on the basis of an estimated produc- 
tion of more than one-half of the total productivity as obtained from 
the quadrat measurements would be unwise, since such a policy 
would tend to lower the carrying capacity below what would be 
maintenance capacity for the area under stock. 
(3) A map is submitted, showing the approximate distribution 
of the different forage-plant associations of the reserve, and descrip- 
tions of the details and possibilities of each are presented. From 
the quadrat measurements the approximate productivity of each 
association is obtained. From these figures and the areas of each 
association a weighted average expression representing the average 
productivity of the whole reserve is derived. This number, 1,110 
pounds per acre, is closely comparable with that obtained as the 
average of the quadrat measurements alone. Assuming the value 
of 1,100 pounds per acre as an average total productivity and 50 
per cent of that amount as maintenance capacity for the range, 
then, if the average animal eats the equivalent of 30 pounds of dry 
feed per day he will need 11,000 pounds in a year, and it will take 10 
acres of land to furnish that amount at full productivity, and 20 
acres of land at maintenance capacity. Thus we have an average 
value for carrying capacity equal to 20 acres per head per year, or 
82 head per section, for the reserve. 
