Biodiversity Characteristics and Carbon Sequestration Potential of Successional Woody Plants Versus Tree Plantation under Different Reclamation Treatments on Hard-Coal Mine Heaps––A Case Study from Upper Silesia

In the discussion about sustainable forestry, a key role is played by the development of ecosystem services, including ecological, social, and economic ones, in which biodiversity and carbon (C) sequestration are among the most important. Afforestation of disturbed and post-mining sites is one of the ways to minimize the negative impact of civilization on the environment. Optimizing C sequestration strategies at post-mining sites plays a crucial role in promoting ecosystem recovery, supporting climate change mitigation, and enabling C offsetting. In this study, we compared the C storage in the soil and plant biomass of forest ecosystems developed on coal-mine heaps for different scenarios of reclamation and succession. We tested combinations of sites (i.e., non-reclaimed sites on bare carboniferous rock [BR] and sites reclaimed by applying topsoil [TS]) and successional woodland and tree plantation. The estimated potential for total C storage (in the soil + biomass) for TS sites ranged from 68.13 to 121.08 Mg ha−1, of which 52.20–102.89 Mg ha−1 was stored in the soil and 12.09–20.15 Mg ha−1 in the biomass. In the non-reclaimed sites on BR, the total C storage was much higher, amounting to 523.14 Mg ha−1 (507.66 Mg ha−1 being in the soil), which was due to the geogenic coal content in the BR. However, the C storage in the biomass (15.48 Mg ha−1) and litter (5.91 Mg ha−1) was similar to the amounts obtained from the reclaimed sites. The number of species did not differ statistically significantly between the analyzed variants. On average, 14 species were recorded in the plots. The average Shannon–Wiener index (H’) value was higher for sites with BR (1.99) than TS variants on reclaimed plots (1.71). The lowest H’ value was for those plots with Robinia pseudacacia in the stand. One of the main implications of the obtained results for sustainable forestry is the perspective of using succession in the recovery of a disturbed ecosystem. We noted that woodlands from succession on BR are highly biodiverse, have high C sequestration potential, and do not require time-consuming reclamation treatments.