Reclamation patterns vary carbon sequestration by trees and soils in an opencast coal mine, China

- Carbon sequestration and distribution in reclaimed forest ecosystems were explored.
- Soil contributed a higher portion of the total carbon than plant.
- Mixed forests facilitated C sequestration than pure forests.
- R. pseudoacacia-P. tabulaeformis forest accumulated more plant C and soil C.

Reforestation is often recommended for ecological restoration in mining areas because of tree's high stand-level productivity and satisfied carbon (C) and other nutrient sequestration objectives. However, the C sequestration efficiency of different plantation patterns or different tree species is rarely understood. In order to get insight of the C sequestration efficiency by trees and soils of different reclamation patterns in Pingshuo opencast coal mine, Shanxi Province, China, three different reclamation patterns (developed for 17 years) at three permanent fixed plots, broadleaf mixed forest: R. pseudoacacia-U. pumila-A. altissima (Plot code: BM), broadleaf conifer mixed forest: R. pseudoacacia-P. tabulaeformis (Plot code: BC) and broadleaf monoculture forest: R. pseudoacacia (Plot code: BR), were selected and investigated. The results showed that tree volumes and biomass differed significantly after 17 years' succession, from 21.58 m3 and 36.02 Mg ha− 1 of the broadleaf monoculture forest (BR) to 37.20 m3 and 48.73 Mg ha− 1 of broadleaf conifer mixed forest (BC). Accordingly, tree C and litter C were observed higher in BC (24.37 and 2.26 Mg ha− 1) than BM (19.25 and 1.15 Mg ha− 1) and BR (18.01 and 1.31 Mg ha− 1). Herb C, however, was observed lower in BC (0.02 Mg ha− 1) than BR (0.25 Mg ha− 1) and BM (0.24 Mg ha− 1). C sequestrated in soil organic matter varied in the order: BC (172.16 Mg ha− 1) > BM (73.79 Mg ha− 1) > BR (51.59 Mg ha− 1) and the top layer (0-20 cm) C contributed a large portion (varied from 37% in BC to 53% in BM) of the total soil C. Consequently, BC sequestrated the highest total C (198.81 Mg ha− 1) by plant, litter and soil, followed by BM (94.43 Mg ha− 1) and BR (71.16 Mg ha− 1). In regard to the total C distribution, a major portion of the total C consisted of soil C (varied from 72.49% in BR to 86.60% in BC). Overall, this study indicated that mixed forest facilitated sequestrating more C than pure forest, and the broadleaf conifer mixed forest: R. pseudoacacia-P. tabulaeformis not only accumulated more plant biomass but also accelerated the soil C sequestration which may be suggested as the more suitable pattern for the opencast coal mine reclamation in the region of eastern Loess Plateau of China.