Development of earthworm populations in afforested colliery spoil heaps innorthern Bohemia, Czech Republic

The majority of colliery spoil heaps, taking up several square kilometres o f a post-mined landscape in the open cast coal mining area near Sokolov (no rthern Bohemia), have been reclaimed using afforestation. In a pilot study, earthworm populations were compared between heaps of the same age afforest ed with different tree species. A significant effect of tree species on ear thworm assemblages was found; both density and species richness were much h igher in alder stands than in those of larch, oak or a mixture of birch, sp ruce and exotic coniferous trees. Subsequently, earthworms were studied at five heap sites representing a chronosequence-of black alder stands (Alnus glutinosa, age 3-62 years) and compared with the community of an alder stan d (50 years old) on natural soil. The density of earthworms was increasingl y higher from the youngest stand (89.3 ind . m(-2)) to the older ones (e.g. 253.0 ind . m(-2) in 34 years old stand), but was lower again in the oldes t stand (96.0 ind . m(-2)). Populations comparable to those in undisturbed forest (154 ind . m(-2)) were established as early as within 7 years. There were, however, marked differences in community structures among individual stands. The young plots were solely colonised by euryecious epigeic earthw orms; higher proportions of endogeic species did not appear until after mor e than 30 years of succession. Even in the oldest stand, the community was quite different from that in the undisturbed forest, the latter being domin ated by the litter-feeding species Dendrobaena vejdovskyi.