221 THE ECOLOGY OF THE CENTRAL COASTAL AREA OF NEW SOUTH WALES. III. TYPES OF PRIMARY SUCCESSION. By Ilma M. Pidgeon, M.Sc, Linnean Macleay Fellow of the Society in Botany. {From the Botany School, University of Sydney.) (Plates vi-viii; fourteen Text-figures.) [Read 29th May, 1940.] Introduction. An analysis of the vegetation on the central coastlands of New South Wales type illustrates clearly that in any natural region the same climax is reached whether the succession begins in water, on rocks, or on wind-blown sand. A study of the mosaic of vegetation in this area reveals evidence of successions from xerarch and hydrarch conditions culminating in Eucalyptus Forest. The purpose of this paper is to place on record a summary of the successions of vegetation of the central coastlands, and to discuss difficulties in the application of the concept of succession to this vegetation. The concept of plant succession was proposed by Cowles (1901) to aid his classification of the vegetation around Chicago. He adduced for that district abundant evidence of physiographic development on sand dunes and rocks, in lakes, and in river valleys, and this development was accompanied by a succession of plants. Where there was a stable landscape, there was an apparently stable vegetation, the climax. The prime factor of the environment which determined the stage of succession reached in any habitat was water; habitats could be broadly defined as wetter or drier than the normal habitat which carried the clirnax. This idea of succession was subsequently elaborated, burdened With a special nomenclature (Clements, 1916) and even endowed with philosophical significance (Phillips, 1935). It was applied to vegetation in other parts of the world, often with striking success (e.g. the work of Tansley and Watt), but on the Hawkesbury Sandstone in the central coastlands of New South Wales the difficulties in classi-fying vegetation are not totally overcome by using the principle of succession. In this paper, the opportunity is taken to discuss these difl[iculties and to put forward a few suggestions as to how they may be surmounted. Types of Primary Succession. The climate and physiography of the district have been described in earlier publications of this series (Pidgeon, 1937, 1938). It is convenient to consider five different types of primary succession. The habitats available for colonization along these five developmental lines are: (i) Tidal mud flats. — Owing to the absence of delta-forming rivers, these are restricted to the arms and bays in the upper reaches of the estuaries which dissect the coastline. Saline flats are characterized by mangrove swamps.
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