Dark Island heath (Ninety-mile Plain, South Australia). I. Definition of the ecosystem

Abstract

A survey of the literature on the distribution of the sclerophyllous understorey in Australia leads to the conclusion that, although the climatic conditions under which it grows may vary considerably, the soils on which it flourishes are always acid and very low in available phosphorus and nitrogen and sometimes in potassium, copper, zinc, and molybdenum. The problem is how the sclerophyllous species are able to flourish on such deficient soils.

To provide a background for the investigation of this problem, a detailed ecological study was initiated on an extensive stand of heath occurring on deep sand (the Makin sand) in the upper south-east of South Australia. This paper outlines the habitat and indicates the general characteristics of the heath vegetation of the area.

The climate is typical of a meditsrranean region; the soil is a deep, acid sand, remarkably low in most mineral nutrients; the vegetation is scarcely influenced by grazing animals, but is regularly razed by fire.

The vegetation is dominated by a number of nanophanerophytes, not more than 6 ft in height, with an understorey of chamaephytes, hemicryptophytes, and geophytes. The majority of the species possess dull green, small, sclerophyllous leaves (leptophylls). Growth occurs predominantly during the summer, from January to March, while many of the species flower during spring. Most of the dominant species, however, flower during late summer to midwinter. Leaf-fall is greatest towards the end of the dry summer period, while litter decomposition, which is only completed after 1 1/2– 2 1/2 years, reaches its maximum in the spring.

It is shown that it is necessary to examine at least four random quadrats of at least 25 sq. yd to study satisfactorily the larger species. In each quadrat, a smaller random sub-quadrat of at least 22 sq. ft will enable the critical examination of the smaller species.

The outstanding features of the southern Australian heath are (1) a summergrowth rhythm instead of the spring growth typical of similar vegetation in other mediterranean-type regions, and (2) its consistent occurrence on soils very low in fertility. It is suggested that these are connected with the evolutionary history of the heath which apparently flourished during the Pliocene period on widespread, infertile, lateritic podsols in equilibrium with a warm pluvial climate favouring summer growth.