THE ABUNDANCE AND DIVERSITY OF EARTHWORMS IN PASTURE SOILS IN THE FLEURIEU PENINSULA, SOUTH-AUSTRALIA

Earthworms were surveyed in 113 pasture soils in the Mount Lofty Ranges, Fleurieu Peninsula, South Australia, in a region where annual rainfall is 600-1200 mm and the climate is mediterranean. The soils within these pastures included a variety of profile forms (e.g. sandy soils with yellow, brown or red clays in the B horizon; uniform coarse textured sands). The most widespread earthworm species were Aporrectodea trapezoides (found at 95% of sites), Microscolex dubius (61%), Aporrectodea rosea (38%) and Aporrectodea caliginosa (36%). These are all introduced species. The total densities of earthworms varied from 0 to 608 m-2 (mean = 169.2). At most sites (66%), densities were <200 m-2. Native earthworms were present at 40 sites but their total densities exceeded 100 m-2 at only 7 sites. The species richness and diversity of the earthworm communities were low; never more than 5 species were found in any one pasture (mean = 3.1). The abundance of the introduced species (all species combined) varied between soil profile forms, being least in the uniform sands. No such variation was found for native species. Several significant, but weak, correlations were obtained between the numbers and weights of earthworms and other environmental variables (e.g. rainfall, depth of A horizon, % sand, clay, nitrogen and carbon). Stepwise multiple regression of the numbers and weights of introduced species against these environmental variables suggested that % clay was the most important regressor. The potential for increasing the abundance and diversity of earthworms in Australian soils is discussed.