Carbon storage in post-mining forest soil, the role of tree biomass and soil bioturbation

Carbon storage in aboveground tree biomass and soil organic matter (in depth of A layer development i.e., up to 20 cm) was studied in 22-32 year-old post-mining sites in the northwest of the Czech Republic. Four replicated sites afforested with different tree species (spruce, pine, larch, oak, lime or alder) were compared with sites left to natural regeneration which were dominated by aspen, birch and willow. No topsoil was applied at the sites; hence carbon accumulation resulted from in situ soil development on alkaline tertiary clays that were dumped on the heaps. In aboveground tree biomass, carbon storage ranged from 17.0 ± 5.9 (mean ± SEM) to 67.6 ± 5.9 t ha⁻¹ and the rate of C accumulation increased from 0.60 ± 0.09 to 2.31 ± 0.23 t ha⁻¹ year⁻¹ (natural regeneration < pine < spruce < oak < lime < alder < larch). Carbon storage in soil organic matter varied from 4.5 ± 3.7 to 38.0 ± 7.1 t ha⁻¹ and the rate of C accumulation in soil organic matter increased from 0.15 ± 0.05 to 1.28 ± 0.34 t ha⁻¹ year⁻¹ at sites in the order: natural regeneration < spruce < pine, oak < larch < alder < lime. Carbon storage in the soil was positively correlated with aboveground tree biomass. Soil carbon was equivalent to 98.1% of the carbon found in aboveground tree biomass at lime dominated sites, but only 21.8% at sites with natural regeneration. No significant correlation was found between C storage in soil and aboveground litter input. Total soil carbon storage was correlated positively and significantly with earthworm density, and occurrence of earthworm cast in topsoil, which indicated that bioturbation could play an important role in soil carbon storage. Hence, not only restoring of wood production, but also restoring of soil community is critical for C storage in soil and whole ecosystem.