Performance of the earthworm Aporrectodea caliginosa on unreclaimed spoil heaps at different successional stages

• We studied earthworm performance on spoil heaps of different age.
• Earthworm biomass and abundance was affected by site age.
• Litter quality and tree canopy influenced earthworm performance.
• Earthworm presence on spoil heaps is affected by site age and character of vegetation.

Earlier studies of post-mining soils near Sokolov, Czech Republic, showed that colonization of the spoil heaps by earthworms greatly changes the plant community composition and soil characteristics. The current study determined how colonization of heaps by the endogeic earthworm Aporrectodea caliginosa is affected by the vegetation, litter, and soil at sites of different ages. In one experiment, we measured the performance of A. caliginosa in 25-l microplots at four heaps of increasing age and successional stage (8, 15, 25, and 48 years). After 6 months, A. caliginosa number and biomass in microplots decreased in young heaps (8 and 15 years old), remained constant in the 25-year-old heap, and increased in the 48-year-old heap. In other words, A. caliginosa survival, growth, and reproduction increased with successional stage. In a second field experiment, we tested A. caliginosa performance in microplots containing different types of litter at two heaps at mid-successional stages (19 and 25 years old). After 12 months, A. caliginosa biomass and abundance were greater with grass litter than with shrub and tree litter, but were greater in the 25-year-old heap, which was dominated by shrubs, than in the 19-year-old heap, which was dominated by grasses. Together, the two experiments indicate that colonization of heaps by A. caliginosa is enhanced by succession and by remaining patches of early successional vegetation in heaps at mid-successional stages.