109 



There is need of further investigation of the saltbush flora in Australia, 

 but pending the pubHcation of further work on the subject, it may be said 

 that saltbush is considered as essentially an arid and not a halophytic formation. 

 A saltbush plain of the type described above is a serai unit in the formation 

 as displayed on the mainland, but the Atriplex paludosnm consocies on Pearson 

 Islands is, in that locality, a subclimax. It is related to Rhagodia crassifolia 

 consocies, which is the most stable community on Franklin Island. This is 

 shown by the interesting occurrence of local patches of Rhagodia crassifolia in 

 the saltbush on Pearson Islands. Rhagodia crassifolia open shrubland was con- 

 sidered a subclimax on Franklin Island, but I now regard the succession sug- 

 gested, i.e., towards a scrub woodland involving Melaleuca parviflora, as mis- 

 taken. The examination of Pearson Island shows that Melaleuca parviflora 

 properly has its place in a different and less xerophytic line of succession. 



The woodland series on the hill slopes shows a greater number of suc- 

 cessional stages than the saltbush ; this is to be expected in a less arid sequence. 

 It is a formation of less xerophytic type, as is shown by the occvn"rence of 

 mosses, Chcilanthes tenuifolia and Calythrix tetragona. The two last grow on 

 the Mount Lofty Ranges in a rainfall of over 30 inches. Casiiarina stricta 

 consocies is a closed community at the higher levels. This species on the main- 

 land does not form a climax associaton, but is an early stage in the sclerophyllous 

 woodland series. Casuarina stricta in South Australia is characteristic of rocky 

 outcrops, where it obtains deep but well-drained soil. On Pearson Island the 

 forest succession goes no further than the Casuarina woodland, the edaphic 

 factors as well as such a climatic factor as wind militating against the growth of 

 most trees. 



The Melaleuca parviflora consocies is a scrub woodland of a more xerophytic 

 type than the Casuarina woodland. Melaleuca parviflora forms dense thickets 

 of considerable extent on some of the neighbouring islands, e.g., Flinders Island, 

 and also on the mainland. On the mainland, however, it is certainly a stage in 

 the sere culminating in mallee (Eucalyptus spp.). 



The accompanying figure shows graphically the relationship between the 

 communities on the granite slopes : — - 



Casuarina stricta Melaleuca parviflora. 



consocies. consocies. 



Casuarina stricta with Melaleuca parviflora and mixed 

 Leucopogon. shrub community. 



\ 



\ 



Olearia-Leucopogoii Melaleuca habnaturorum 



associes. consocies. 



I I 



Pclargonmm-Mesenibryantheinum-Poa Arthrocnenmm and dwarf 



associes. halophytic communities. 



\ / 



Bare granite. 



Fig. 2. 



Diagram to show the relation of the chief scrub and woodland communities on granite. 



The separation of the communities on travertine limestone into another 

 group is a matter of convenience rather than an expression of difference. A 

 saltbush flora develops upon travertine areas upon the mainland, for travertine 

 limestone, of course, is not so much a geological formation as an indication of a 

 climate with a high evaporation rate. On Pearson Island we find an open 

 community with Atriplex paludosum as the dominant species upon parts of the 

 plateaux. It is possible that some, at least, of the travertine communities should 

 find their place in the saltbush formation, but at present it is preferable to group 

 all the limestone communities together. 



