Soil carbon accumulation after open-cast coal and oil shale mining in Northern Hemisphere: a quantitative review

Meta-analysis and other statistical methods were used to evaluate how changes in soil organic carbon (SOC) content in post-mining soils are related to different factors; the data were obtained from 17 studies covering 93 temperate post-mining sites in the Northern Hemisphere that had been revegetated by forest or grassland either by reclamation or natural succession. Because many studies have failed to report any measures of variance, only part of the data were used for meta-analysis. According to the meta-analysis, the rate of SOC accumulation was unrelated to vegetation type. In a separate analysis that included all available data and in which rates of SOC accumulation at each site were used as individual entries, the rate of SOC accumulation differed depending on the age of the site and vegetation type. Under deciduous forests, the rate reached a maximum after 5–10 years and then decreased. Under coniferous forests, the initial SOC values were lower than under deciduous forests, but slowly increased with age and reached a maximum after 30–40 years. No significant temporal trend was found in grasslands, probably because the data set included only relatively young grassland sites. Based on data from sites younger than 30 years, sites with grasslands and deciduous forests accumulated SOC faster than sites with coniferous forests. The rate of accumulation was negatively correlated with temperature under coniferous forests, but positively correlated with temperature in grasslands. This suggests that carbon sequestration is favored by cold climates in coniferous forests, but by warm climates in grasslands. Deciduous forests were intermediate. Compared to conifers, deciduous trees may support SOC sequestration deeper in the soil profile, which may enhance SOC stability. A large proportion of post-mining sites reach the pre-mining SOC stock within 20 years or less after reclamation.