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 practica l indicators in land quality evaluation. The abundance and distribution of earthworms were determined in 84 cropping and pasture soils in north-east V ictoria 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. I ntroduced lumbricid earthworms, Aporrectodea trapezoides and A. caliginosa were the most widely distributed (88% and 61% of all sites, respectively) a nd numerically dominant (respective population densities of 35.8 and 32.1 m (-2)). Soils under pasture supported on average 3.2 times more earthworms t han those under cropping. The age structure of populations varied with spec ies, introduced lumbricids and acanthodrilids displayed an adult-dominant s tructure and the native megascolecids displayed a juvenile-dominant populat ion. Indigenous earthworms belonged to a single genus, Spenceriella. Whilst not occurring in high densities these indigenous earthworms were widesprea d in their distribution and their numbers were negatively correlated with s oil 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 containi ng >100 earthworms m(-2), 25 received MATP in excess of 600 mm. Correlation s between earthworm densities and a range of physical and chemical paramete rs were generally poor. This may highlight the short-comings of these param eters in describing distribution patterns. (C) 1999 Elsevier Science B.V. A ll rights reserved.