is likely that a considerable regeneration of shrubs occurred in this portion of the 

 third period. 



Fourth period (1924- 1936). The sheep population increased from 278,000 to 

 314,000 during a sequence of dry years from 1925- 1929 inclusive, as a result of re- 

 generation of pastures during the previous stage. Numbers continued to increase to 

 540,000 sheep during the short term phase of high rainfall 1930- 1932, but receded to 

 338,000 with the resumption of the dry cycle to 1936. The general level of sheep 

 numbers rose from a ten year mean of 220,000 at the beginning of the whole period 

 to one of 400,000 at the end. 



Fifth period (1936- 1951). The mean level of 400,000 sheep reached in the 

 previous stage has been maintained, with some fluctuations, during the recent period 

 from 1936- 1951, indicating that at this level sheep numbers are in equilibrium with 

 the present condition of the pastures. The general pattern of high rainfall over these 

 years is interspersed with two short phases of unfavourable seasons during which 

 the recession in sheep population was aggravated by wartime conditions. From 1945 

 - 1951, numbers of sheep rose from 318,000 to 478,000; during these favourable 

 seasons very marked regeneration of shrubs has occurred. 



The pastures of the region are now at a stage when sound measures of manage- 

 ment related to foreseeable rainfall trends can lead to a considerable degree of im- 

 provement of both the capital resources and permanent productivity. On the other 

 hand, a repetition of earlier mismanagement may lead to another recession of the 

 pastures and widespread denudation. The investigations at Yudnapinna have indi- 

 cated that greatly increased productivity may be achieved by a closer subdivision of 

 pastures and the provision of better and more frequent water supplies. 



Conclusions 



The more effective utilization of arid and semi- arid pastoral areas depends 

 upon the recognition of four outstanding principles :- 



(1) An analysis of the climatic resources, and especially rainfall, in the long- 

 term, with due allowance for evaporation rates and the inevitable groups of 

 drought years. 



(2) The use of fencing to provide for appropriate grazing management. 



(3) Multiplication of the points at which livestock can secure water. 



(4) The adjustment of stocking rates to the variations of the forage supply which 

 are consequent upon the long-term climatic pattern. 



These principles are of general application to arid regions and their adoption 

 could lead to a very substantial increase in the productivity of both hot and cold 

 deserts, provided (a) that there is a minimum quantity of moisture available for 

 transpiration of the order of 2 inches per year and (b) that growth is not inhibited 

 by low temperatures, of the order of monthly means of 40-45°F or less, during the 

 period over which moisture is available to plants of value for permanent grazing. 



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