Assessment of biological soil quality in wooded reclaimed mine sites

Species numbers and biomass of earthworms increased nearly continuously from the 3rd to the 46th year after recultivation, reaching 100 g m−2 at the oldest sites. This development is characterised by a decreasing proportion of epigeic life forms. In contrast to data from coniferous afforestations in Berzdorf mine sites and other mine sites studied in Lower Lusatia as well as from the literature, the earthworm development on Berzdorf mine sites with deciduous afforestation appear as an ideal and regionally typical development series (ITDS). Earthworm populations at 13 Lower Lusatian mine sites 35–50 years after afforestation were found to have a biomass between 0.1 and 21 g m−2, dependent on humidity and kind of litter (pine, beech, oak, alder, poplar, lime). An increase of earthworm biomass above 20 g m−2 was accompanied by a change of humus type from mor via moder to a mull humus. At the same point the biomass share of the humiphagous macrofauna other than earthworms (Diplopods, Isopods, Diptera larvae) decreased, i.e. the biomass of earthworms became more and more dominant. Further information comes from the comparison of the yearly input of dead soil organic matter (SOM), measured as the energy content of the yearly litter fall out and field layer production, and as the potential ability of the soil humiphagous fauna to decompose the yearly supply of SOM, expressed as the potential zootic decomposition level (DLZpot; kJ m−2 a−1). A very high litter production 3–5 years after afforestation is combined with a low DLZpot, caused by the absence of earthworms, thus leading to a high ectohumus layer. As soon as earthworm biomass rises (after 10 years), the DLZpot becomes very high, later levelling out depending on primary production, and causing a mull humus type. Microarthropods (Collembola, Actinedida, Oribatida, Gamasida) colonised young mine sites with deep deciduous litter layer very quickly and in high densities (>100.000 ind. m−2). Later on, the rising competition with earthworms caused a decline of microarthropods, followed by a second maximum after about 30 years. At the oldest studied sites, the density reached a level near to that of a neighbouring native woodland. On pine afforestations, the colonisation needs more time but reaches the highest observed density (>250.000 ind. m−2) after 30 years. In parallel to the earthworms, the quantitative development of microarthropods on deciduous mine sites can be taken as an ideal and regionally typical developmental series (ITDS). At the species level, 8 colonising groups of Collembola could be distinguished according to the centre of their temporal occurrence. Besides fugitive initial species at the start and stenoecious woodland species at the temporary finish, 6 groups were found to be typical for certain periods of the mine site development. In contrast to the Collembola with 99 species found at the mine sites, only 14 species of predatory centipedes were observed, but as within the Collembola, the centipedes showed a species-specific colonisation behaviour, also marking certain periods of ecosystem succession on the mine sites.