The Effect of the Stratification of Vegetation on the Analysis of Successional Data

Abstract

Hierarchical classification techniques have been applied to such diverse vegetation communities as heathland (Williams & Lambert 1959, 1960, 1961), tropical rain forest (Webb et al. 1967; Flenley 1969), desert floral associations (Bradley 1971), stranded coastal sand dune vegetation (Welbourn & Lange 1968), Nigerian savanna (Kershaw 1968; Hopkins 1968), and an oak-hickory forest in Tennessee (Grigal & Goldstein 1971). Apart from the studies by Webb et al. and to a certain extent of Grigal & Goldstein and of Hopkins, the relationship between different life forms has not been studied. The reason for this is either the paucity of the species occurring in the various synusiae or the terms of reference of the investigation. Webb et al. (1967) have attempted to analyse different life forms in a tropical rain forest, with some degree of success. From the analysis of ten classes, into which the species present at the sampling sites were assigned, the study revealed that the rain forests comprise two elements: the large plants of the canopy, which respond to the macro-climate, and secondly all the plants of the understorey which principally reflect edaphic factors and minor local variations in soil disturbances. The study was thus concerned only with compositional details of vegetation and not with data pertaining to a vegetation succession. Grigal & Goldstein (1971) employed a stratified random sampling scheme. At each sampling site the woody vegetation was sampled by a nest of three concentric circles. However, in the analysis of the data, no distinction was made with regard to these strata and their relationships. Only the relative importance of each species was found. The results that Hopkins (1968) obtained from samples collected, both in time and space, divided the vegetation in his study area into three groups, the grass savanna, the savanna woodland and the tree savanna. Since the data analysed were in the form of those species present at a sampling site the relationship between species growing in different layers could not be explored. This paper presents some of the results of a quantitative study conducted on a coastal sand dune vegetation succession, at Deep Creek near Nambucca Heads, mid-north coast of New South Wales, Australia (Fig. 1). It has been recognized by Williams et al. (1969) and Allen (1971) that few quantitative studies of vegetation successions have been undertaken. Since there is a complex physiognomic assemblage of species at Deep Creek, the effect of plants, in the various layers of the vegetation, on the analysis of the vegetation successions could be considered. The area of study consists of a main dune crest which is flanked on its seaward side by