90 CARNEGIE INSTITUTION OF WASHINGTON. 



Plant Habits and Habitats in the More Arid Portions of South Australia, 



by W. A. Cannon. 



The following are some of the more important conclusions and 

 results derived from a field study of the vegetation in central, northern, 

 and southwestern South Australia in 1918. 



An important feature of the physical environment of the State is 

 the amount and character of the rainfall. Over the northern portion, 

 consisting approximately of 75 per cent of the land area, the total 

 precipitation is 10 inches or less. Much of this region is the great 

 artesian basin of central Australia and is partly below sea-level. An 

 area estimated at 3 per cent or more, lying wholly within this basin, 

 receives 5 inches or less of rain annually. It is proposed to term regions 

 of South Australia which have a rainfall of 5 inches or less each year 

 desertic or eremaic, and regions with an annual precipitation between 

 5 and 10 inches as arid. Where the rainfall is between 10 and 15 inches 

 the regions will be referred to as semiarid or subarid. 



The rainfall of South Austraha is periodic. About 76 per cent falls 

 in the cool season, the largest proportion of which occurs in the southern 

 half of the State. The monsoonal rains of summer are of importance 

 in the Far North, where, however, neither the cyclonic winter rains or 

 the summer monsoons are dependable. Since the rainfall is periodic, 

 the rainless periods are also regular in their occurrence and are of 

 undoubted importance in shaping the leading features of the perennial 

 vegetation. In arid South Australia the number of rainless days each 

 year is 300 or over, and that in the semiarid regions is about the same, 

 while in the eremaic districts it may exceed 340. 



A marked feature of the rainfall is the number of storms in which 

 the precipitation totals 0.15 inch or less, and this is a characteristic 

 most marked in the driest regions. At Oodnadatta, for example, where 

 the rainfall averages 4.68 inches annually, about 31.2 per cent of the 

 entire precipitation occurs in such small amounts. In one year as much 

 as 56 per cent of the entire rainfall at Oodnadatta was received in 

 storms of this kind. Where rain occurs in no greater amount than 

 0.15 inch, or even more than this, it does not moisten the soil to a 

 depth useful for roots, and the configuration of the surface of the soil 

 of itself is, under such conditions, of no moment. The effective rain- 

 fall in the desert, therefore, is considerably under that presented in 

 official summaries. 



South Australia has a mild temperate climate, with hot summers, 

 especially in the north, and cool winters. In the far north (William's 

 Creek) a maximum shade temperature of 119.1° F. has been recorded. 

 The daily variation in temperature may be 40° F. or more. The shade 

 temperatures of the far north reach or exceed 90° F. for about one- 

 third of the year. In approximately 64 per cent of the state, in a 



