geazijstg eanges in southern aeizona. 39 



of southern Arizona and possibly to an even larger area. Eecords 

 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 gTound. Stock always get 

 less than this amount. 



(2) Eecords 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 492^ acres. The average amount of hay obtained is 

 640 pounds per acre. Three areas, each about an acre in extent, 

 which had the ha}^ 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 is 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 carrjdng 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 jproductivity, 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 

 32 head per section, for the reserve. 



