Vertical distribution of soil fauna and microbial community under two contrasting post mining chronosequences: Sites reclaimed by alder plantation and unreclaimed regrowth

Vertical distribution of soil biota is not well understood. Here we studied the development of vertical distribution of soil chemical and biological properties in two post-mining chronosequnces in heaps after open cast coal mining, one left to succession (sites 20, 35 and 60 years old) and one reclaimed by levelling and Alder (Alnus glutinosa and Alnus incana) afforestation (sites 10, 25, 40, and 60 years old) near Sokolov, Czechia. When spoil material is compacted during levelling and afforestation, as in reclaimed sites, the effect of time in soil biota development was less important than in spontaneous succession where no compaction occurs. Soil depth was a stronger explanatory factor in explaining the soil microbial biomass variations under reclamation regimes while comparatively less strong under spontaneous succession which points at the impact of spoil compaction on vertical development of organisms. Spontaneous succession encourages a more diverse and dynamic vertical, as well as horizontal, faunal community development, especially across time. Breaking down fauna into ecological subgroups, time was more of an important factor for fauna active below ground (endogeic), than for surface-dwelling fauna likely due to further soil profile development by time. Calculated depth in which 90% individuals occur shows that considering only the depth of 0-10 cm overlooks a substantial part of some faunal groups (e.g. Pauropoda and Symphylan) that are abundant in deeper layers. Soil depth is also more of a strong predictor of soil biota than soil C content, indicating that the population decrease in soil biota community with depth cannot be explained only by decreasing organic matter content.