Species distribution over part of the Coonalpyn Downs, South Australia

Abstract

An account is given of edapho-climatic ranges and species area of elements of the mainly sclerophyllous vegetation of a representative portion of the Coonalpyn Downs. Eucalyptus, Melaleuca, Acacia, Hakea, Leptospermum, Casuarina, and Callitris are the principal genera discussed.

Water relations as governed by soil profile characteristics, landscape position, and the depth and salinity of water-tables are considered to be the main factors influencing plant distribution. The rainfall gradient across the area is gentle and rainfall as an independent factor only appears to influence water relations sufficiently to affect species distribution in a few cases. The fertility of soils on sandplain and sand dunes is invariably of a low order and a species composition typical of higher fertility soils is usually only found on inliers of such soils. Subsidiary edaphic responses include gross changes in soil reaction and soil salinity.

A few indicator species in a given plant community can be associated with some particular soil characteristic and such correlations are distinct from community responses. For example, Hakea vittata in heath is generally associated with sandplain soils with a lime pan or a calcic subsoil within 2 ft of the surface.

An examination of the area of numerous species shows that there is considerable variation across the territory in the composition of communities with repetitive dominants.

Evidence is presented that suggests that species migrations may have spread from refuges or at least continuously vegetated areas within the territory as well as from outside it. The poor correlation between the area or limits of centres of frequency of some species and their observed edapho-climatic ranges suggests that migration is still occurring and that the climax community has not been produced in all cases.