244 



ON THE ZONATION OF THE VEGETATION IN THE PORT WAKEFIELD 

 DISTRICT, WITH SPECIAL REFERENCE TO THE SALINITY OF THE 



SOIL. 



By Professor T. G. B. Osborn, D.Sc, and 

 J. G. Wood, B.Sc, Department of Botany, University of Adelaide. 



[Read September 13, 1923.] 



Plate XX. 



This paper embodies the results of a reconnaissance visit made in March 

 of this year to the Port Wakefield district. The object was to study the zonation 

 of the vegetation when passing from a community of undoubted halophytes to a 

 "saltbush" community. 



Saltbush is the name given in Australia to various annual or half-shrubby 

 perennials belonging to the Chenopodiaceae, especially to the genus Atriplex. 

 The plants have characteristically grey, more or less fleshy leaves, which, as the 

 common name implies, contain a quantity of sodium chloride. Saltbushes grow 

 abundantly over the arid portions of Australia, and are of considerable economic 

 importance, because they provide a reserve of fodder for the pastoral industry. 

 In the dry season, or in times of drought, stock can live entirely on the leaves of 

 these plants. 



Because of their appreciably salt taste, these bushes have been regarded as 

 characteristic of a soil with a high saline content, that is halophytes. The 

 Chenopodiaceae, as a family, contains a large number of halophytes, and the 

 Atripleces of Australia have often been regarded as belonging to this biological 

 group of plants,'^^) apparently, largely on general grounds. 



Last year one of us, in company with R. S. Adamson, w^as led to express 

 the opinion that in some cases, at any rate, the Australian saltbushes did not 

 appear to be halophytic.'^'^ At that time we had no more positive data to offer 

 than our observations upon the distribution of the plants in the field. Recently, 

 when studying the vegetation of Pearson Islands,'*^^) it v/as found that a typical 

 saltbush community, composed of Atriplex paludosum, was developed on soils 

 of only average salinity (NaCl 20 per cent, of the air dry soil). 



Observations on the flora of the arid portions of South Australia have 

 been in progress in this Department for some time. It seems useful, however, 

 to preface the accounts with a piece of field work, if only of the reconnaissance 

 type, that should involve a direct comparison between saltbush and plants of 

 the salt marshes, i.e., true halophytes. The results, it is believed, have sufficient 

 general interest to justify their separate publication. 



TOPOGRAPHIC. 



Port Wakefield stands on the eastern shore of Gulf St. Vincent, about five 

 rniles south-south-east from the head. The railway station is only 18 feet above 

 high-tide mark, and the country north and south of the township extends as a 



(1) Maiden, J. H., "Australian Vegetation," in Federal Handbook on Australia, p. 191, 1914. 

 Cannon, W. A., "Plant Habits and Habitats in the Arid Portions of Australia," Carnegie Inst. 

 Publ., No. 308, 1921. 



C^) Adamson, R. S., and T. G. B. Osborn, "On the Ecology of the Ooldea District," Trans. 

 Roy. Soc. S. Austr., xlvi., p. 554, 1922. 



•(3) Osborn, T. G. B., "Flora and Fauna of Nuyts Archipelago and the Investigator Group, 

 No. 8, On the Ecology of Pearson Islands," Trans. Roy. Soc. S. Austr., xlvii., p. 106, 1923. 



