The reclaimed coal mine ecosystem diverges from the surrounding ecosystem and reaches a new self-sustaining state after 20-23 years of succession in the Loess Plateau area, China

Whether or not the completely destroyed ecosystem would follow a succession trajectory towards the surrounding forest ecosystem after restoration remains debatable. Here, a comprehensive dataset of thirty-five ecosystem functions were measured on five reclaimed opencast coal mine forest plots (two Robinia pseudoacacia - Pinus tabuliformis mixed forests with different technosol conditions: RP_T and RP_M; one R. pseudoacacia - Ulmus pumila - Ailanthus altissima mixed forest: RUA; one Picea meyeri - Picea wilsonii - Hippophae rhamnoides mixed forest: PPH; one R. pseudoacacia monoculture forest: RM) and one natural forest plot (Populus simonii monoculture forest: PM) in Pingshuo opencast coal mine, Shanxi Province, China. These functions were employed to examine the reclamation effects among plots in terms of four management scenarios (i.e., biomass productivity, carbon sequestration, general biodiversity conservation and nutrient accumulation) and to determine the affinities between reclaimed ecosystem and its native counterpart according to Bray Curtis Distance Algorithm. The results showed that after 20-23 years of succession, thirty-five ecosystem functions differed among plots and eight highest ecosystem functions were found in RP_T and RP_M (P < 0.05). In scenarios of biomass productivity, carbon sequestration, general biodiversity conservation and nutrient accumulation scenarios, RP_M scored 0.645, 0.470, 0.467 and 0.578, respectively. Accordingly, RP_T scored 0.458, 0.447, 0.405 and 0.515, respectively. Consequently, RP_T and RP_M had the highest scores in the four management objectives compared to other plots. With regard to the ecosystem affinities, RP_T was analogous to RP_M. Similarly, RUA and PPH resembled PM and RM, respectively. Overall, the pioneer tree species determined the reclamation quality in the dump in the long term, which could be referred as the "trigger effect" in the succession trajectory in reclaimed ecosystem, and the reclaimed coal mine ecosystem diverged from the surrounding ecosystem and reached a new self-sustaining state after 20-23 years of succession.