555 



Acacia aneura, and sometimes Piffosporum i^hillyiaeoides ; 

 while in the largest, which have most soil, the furthest devel- 

 opment occurs, and Casuarina lepidophloia, forms small scraps 

 of woodland. 



The vegetation of the sandhills stands in marked contrast 

 to that of the Nullarbor Plain. Under the same climatic con- 

 ditions on the sand, even in the most exposed positions, the 

 plant communities are of large woody plants, and the general 

 effect is of some luxuriance. This effect is perhaps more 

 apparent than real, but is certainly marked as compared with 

 the plain. The difference must be attributed to the difference 

 in soil. The loose sand has practically no run-off — all the rain 

 falling percolates into' the soil at once. Further, the sand 

 readily forms a quit^ dry dust mulch on the surface which 

 prevents loss by evaporation, whilst the relatively coarse soil 

 particles carry on a certain amount of condensation. The 

 much finer-grained soil on the plain, on the other hand, will 

 not condense, and, owing to its much greater wat^r-raising 

 power, will lose water by evaporation instead of forming a 

 mulch. As was pointed out above, on the sand we have two 

 distinct sets of communities — those in the hollows and those 

 on the ridges. The former bear a close relation to the com- 

 munities existing in the dongas, but development proceeds 

 further owing to the better soil and the shelter afforded by 

 the ridges. 



Two moderately distinct communities can be recognized, 

 namely, that of Myoporum platycarpum and H eterodendran 

 olei folium and the open forest of Casuariiva. lepidophloi<i . The 

 former occurs where less sand is present. In both cases some 

 developmental stages can be recognized, especially when one 

 compares some of the hollows near the margin of the plain 

 with those further east. The early stages are represented by 

 A triplex vesicarium generally with bushes, especially of 

 Acacia, an^u era , A. Randelliana, and Eremophila Lafrobei. In 

 the Myoporum-Heterodendron phase, which appears as a 

 climax, the A triplex disappears, but the other bushes are still 

 present. When more sand is present the climax appears to 

 be the Casuarina lepidophloia forest. It is noticeable that 

 this, rather than the Myoporum-Heterodendrori community, 

 occupies most of the hollows further east, where the sand has 

 become more distributed. The portions of this forest which 

 have been cut down show a return to the earlier phase with 

 considerable quantities of A triplex vesicaiinm as under- 

 growth. 



The sandhill ridges, as described earlier, exhibit a series 

 of developmental phases of which mallee f Eucalyptus) 

 appears to be the climax. Here again the succession generally 



