Carbon sequestration in a chronosequence of Scots pine stands in a reclaimed opencast oil shale mine

Ecosystems that develop on mine spoil can serve as significant sinks for CO2. The aim of this study was to estimate the rate of carbon accumulation and its distribution along forest ecosystem partitions in young Scots pine (Pinus sylvestris L.) plantations in the Narva oil shale opencast, Estonia. The tree layer was measured in 2004 in 13 stands afforested with 2-year-old seedlings during 1968 to 1994. Three stands (afforested in 1990, 1983, and 1968) were selected for detailed analysis of the carbon sequestration. Soil profiles were sampled in these stands in 2005. Radiocarbon analysis combined with a simple model of litter production was used to differentiate between plant-derived recent carbon and carbon stemming from fragments of oil shale. Total carbon accumulated since afforestation in vegetation, forest floor, and A horizon was 7.8 t.ha(-1) in the stand established in 1990, 34.5 t.ha(-1) in that established in 1983, and 133.4 t.ha(-1) in that established in 1968. Most of the sequestered carbon was allocated to tree stems; their portion increasing with age from 28% to 51%. The portion of recent soil organic carbon increased from 5% to 23%, which shows that soils contribute significantly to carbon accumulation during early forest succession on degraded land.