Interactions between soil development, vegetation and soil fauna during spontaneous succession in post mining sites

More than 50 parameters of vegetation, soil and soil fauna were studied in 27 non-reclaimed post mining sites of various age (1-41 years old) located near the town of Sokolov (Czech Republic). A clay alkaline substrate (pH 8.5) was dumped in heaps; its pH and contents of available calcium and sodium decreased during succession. Total carbon and nitrogen, available potassium and water-soluble phosphorus increased with increasing successional age. In early stages, i.e. before the establishment of a shrub layer, the topsoil was formed mainly from the dumped spoil material. In shrub-dominated sites (14-22 years old), the litter reserve on the soil surface was higher than annual litter production, and a thick fermentation layer developed below the litter layer indicating slow litter decomposition and soil mixing. In older plots (24 year old or older), a humus layer was formed and the thickness of the fermentation layer decreased. Microstructure analysis indicated that earthworm activity, namely the mixing of organic and mineral layers, played a principal role in humus layer formation. No group of soil fauna preferred early successional stages, but tardigrades, bacteriophagous and fungivorous nematodes, and microsaprophagous dipterans, were tolerant to these stages. The density of most fauna guilds increased in intermediate stages with thick fermentation layer. Pauropods and testate amoebae reached highest densities on these sites. Macrosaprophagous guilds of soil fauna, most important for litter decomposition and soil mixing, attained their highest density in the oldest sites. Two clearly separated clusters of sites were distinguished based on TWINSPAN classification of vegetation. The first cluster included sites 1-23 years old, dominated by ruderal plants. Sites 24-41 years old were grouped in the second cluster; forest and grassland species were more frequent here. The presence of humus layer was selected by a discriminant analysis as the strongest predictor to discriminate between these two clusters. All considered ecosystem components, i.e. soil, soil fauna, and vegetation, passed through substantial changes in about the 25th year of succession and their changes were mutually correlated. (C) 2007 Published by Elsevier Masson SAS.