Examination of the seasonal pattern indicates a tendency for seasons of high or 

 low rainfall to bunch together. The sequential nature of dry and wet winter seasons 

 is apparent; the May - August rainfall, and particularly the June rainfall, exhibit a 

 marked suggestion of periodicity. The annual rainfall of the Station, plotted as 10- 

 year running means (Fig. 3.) and extrapolated back prior to 1885 by correlation with 

 other records, and the notes of early, explorations, appears to indicate a long-term 

 repetitive pattern of 20- 25 years of increased rainfall, (e.g. 1870 — 1895) followed 

 by periods of 10-12 years of much lower rainfall (e.g. 1895 — 1905). 



The importance of the climatic factors and particularly the rainfall sequence to 

 the behaviour of desert shrubs, and their utilization for sheep grazing, will be indi- 

 cated in the subsequent discussion. 



Pasture Management. 



Investigations of pasture management at Yudnapinna have been based essentially 

 upon a long- term grazing experiment in which bluebush (Kochia sedijolia) pastures 

 have been subjected to differential rates of stocking with sheep, on thirteen plots of 

 160 acres each since April 1941. The pasture (Fig. 4) consists of an open com- 

 munity of Kochia sedifolia with a mean density of 580 bushes per acre at the commen- 



SHEEP POPULATION OF N.W. DISTRICT 

 IN RELATION TO RAINFALL AT YUDNAPINNA. 

 1870 1880 1890 I900 1910 1920 1930 



I860 



1940 



1950 



I ' I ' I 1 1 I I I I ' ' ' ' I ' ' ' I I ' ' ' ' I ' I ' ' I 



I860 I870 



1880 1890 1900 



^ '*'' ^ '■■ ^ t ' ^ '' t '''■ I ''''!'■■' I '■'''■■■■ I ■ 



1920 1930 1940 1950 



Figure 3- 

 Sheep population of N.W. District in relation to rainfall at Yudnapinna. 



133 



