386 MANGROVE AND SALTMARSH VEGETATION NEAR SYDNEY, N.S.W., 



occupied by mats of Scaevola suaveolens, over 6 feet in diameter, have ceased 

 to exist. 



The alteration of the vegetation covering this beach, suggests that the 

 piling up of sand against the mangrove at the entrance to Cabbage Tree Creek 

 is due to the activity of southerly gales rather than to the continuous and 

 milder action of the prevailing north-easterly winds. (See Jose, etc., 1911, p. 

 136). It is possible, however, that the north-easterly winds carry a load of 

 sand from the dunes behind Cronnlla Beach and that a certain amount of this 

 finds its way to the marehes at Cabbage Tree Creek. 



The chief points of interest at Cabbage Tree Creek, at the present day, are 

 the raising of the level of the tidal marsh by drift sand deposited on the sur- 

 face of the mud, and the gradual blocking of the creek entrance by sand spits 

 and shoals. The effect of both these changes is to lessen the amount of tidal 

 inundation and to bring about alteration in the physical properties of the soil. 



At the present day the tidal marsh at Cabbage Tree Creek presents a 

 I'omples problem for solution. There does not appear to be any marked de- 

 finition between mangrove and saltmarsh fonnations, and within the saltmarsh 

 it is difficult to define the boundaries of tlie plant iissociations. 



As on the marshes near Sydney, the outermost formation at Cabbage Tree 

 Creek is mangrove in which Avicennia officinalis and Aegiceras majus are the 

 only species. At the entrance to the Creek Avicennia and Aegiceras are being 

 buried in drift sand (PI. xxix.. Photo 9). The area between the low tide level 

 and the shore is occupied by saltmarsh which shows some striking differences 

 from saltmarsh at Port Jackson. An interesting feature is the occurrence, 

 throughout the saltmarsh, of gi'oups of Avicennia officinalis. The innermost 

 of these are only reached by the liighest tides and may be regarded as being 

 stranded. Their position in isolated areas within a newer formation is com- 

 I>arable with certain geological formations known as "inliers." These man- 

 grove "inliers" indicate that rise in level of the mud surface has brought about 

 t!ie imposing of saltmarsh flora upon what was once entirely mangrove (Text- 

 fig. 11 and PI. xxxii., Photo 10). 



Extensive areas at Cabbage Tree Creek are populated by dwarf Avicennia, 

 (PI. XXX., Photo 12) in whicli the main trunk is sliortencd and averages about 

 one foot in height. The lateral branches are given off from this stocky trunk 

 and take up a position i)arallel to the ground (PI. xxx.. Photo 11). Hamilton 

 (1919, p. 470) records dwarf Aviceunia at Homebush Bay, on the Parramatta 

 River, and attributes tlieir diminished form to dilution of tidal waters by fresh 

 water from the inland drainage channels. 



Warming (1909, p. 25) refers to the effect of temperature and the length of 

 the vegetative season upon the external morphology of plants. He points 

 out that dwarf forms occur when the vegetative season is short and the tem- 

 perature low, as in arctic regions, or where high temperatures are combined 

 witli low water supply. ITntil a special investigation has been made of soil and 

 temperature relations, the writer is not in a position to offer any reason for the 

 occurrence near Sydney of localised areas of dwarf-^1 mcewnjo. It is sufficient 

 for the present to say that the writer regards this as a definite growth-form 

 and in no way comparable with the general lowering of stature observed in 

 mangroves as they occur farther from the tropics (Schimper, 1903, p. 409). 



In 1916 the saltmarsh at Cabbage Tree Creek, Port Hacking, had pa.ssed 

 through its piimeer phase, Salicornia australis and Suaeda anstralis being in 

 full occupation of the mud immediately behind the mangrove, and in places 

 penetrating through the mangrove to low water level. Other halophytes, such 



