Species abundance of earthworms in arable and pasture soils in south-eastern Australia

Earthworms play an important role in soil ecology and can serve as practical indicators in land quality evaluation. The abundance and distribution of earthworms were determined in 84 cropping and pasture soils in north-east Victoria and southern New South Wales (NSW), Australia. Overall, an average density of 89 earthworms m(-2) was found, with an average species richness of 1-2 per site, indicating relatively low abundance and species poverty. Introduced lumbricid earthworms, Aporrectodea trapezoides and A. caliginosa were the most widely distributed (88% and 61% of all sites, respectively) and numerically dominant (respective population densities of 35.8 and 32.1 m(-2)). Soils under pasture supported on average 3.2 times more earthworms than those under cropping. The age structure of populations varied with species, introduced lumbricids and acanthodrilids displayed an adult-dominant structure and the native megascolecids displayed a juvenile-dominant population. Indigenous earthworms belonged to a single genus, Spenceriella. Whilst not occurring in high densities these indigenous earthworms were widespread in their distribution and their numbers were negatively correlated with soil P, K, and Mg suggesting an adaptation to low levels of soil fertility. Although the relationship between earthworm densities and mean annual total precipitation (MATP) was not close (r(2) = 0.35), of the 33 sites containing >100 earthworms m(-2), 25 received MATP in excess of 600 mm. Correlations between earthworm densities and a range of physical and chemical parameters were generally poor. This may highlight the short-comings of these parameters in describing distribution patterns. (C) 1999 Elsevier Science B.V. All rights reserved.