Variation in megascolecidae earthworm casting under different native vegetation communities in south-east Australia

Megascolecidae earthworm casts (size up to 125 cm³) form a conspicuous layer in undisturbed basalt soils in South-East Australia. These fertile, well structured clay soils form a couplet with native mesic vegetation communities within sheltered sites in the humid zone. Casting is of potential importance to nutrient cycling at these sites since phosphorus fixation is a well established constraint in basalt soils. To explore this, we have initiated the present study, which seeks to determine spatial variability of earthworm activity (as proxied by casting) within and between adjacent native vegetation communities, and the influence of soil moisture and surface litter on casting. This study, conducted during August 2005, is based on 84 permanent 0.25 m² sample plots, constructed within four well defined vegetation communities in the Blue Mountains of South-East Australia (dry sclerophyll, wet sclerophyll, rainforest and an ecotone between the last two which is distinctive at this site). Each vegetation community contains 16 randomly distributed sample plots. To assess the transition between these communities, four sub-zones were created, with 5 random sample plots between each community. The total amount of surface casts increased as the vegetation community became more mesic (dry sclerophyll – rainforest). This trend coincided with an increase in soil moisture of the cast layer and a decrease in the surface litter. The areas dominated by sclerophyll forest produced approximately 3200 g/m² of surface cast material, contrasting to the ecotone and rainforest communities which produced 5139 g/m² and 6888 g/m² respectively. This represents a two fold increase between sclerophyll and rainforest communities. Future work will address the rates of casting to explore seasonal effects.