Below-ground carbon stocks in intact and transformed subtropical thicket landscapes in semi-arid South Africa

The feasibility of restoring subtropical thicket using carbon markets is largely a function of its carbon sequestration potential. We measured below-ground carbon stocks and analysed soil properties in intact, degraded and old agricultural landscapes in Baviaans Spekboom Thicket – a highly degraded thicket type earmarked for restoration. Soil and root carbon stocks to a depth of 110 cm in intact thicket were 93 ± 7 (SE) t ha−1 and 11 ± 2 t ha−1, respectively. Degraded thicket had approximately one-third of the soil (31 ± 2 t ha−1) and one-quarter of the root (2.7 ± 0.3 t ha−1) carbon of intact thicket. Old agricultural lands had approximately half of the soil (42 ± 4 t ha−1) and quarter of the root (2.6 ± 0.3 t ha−1) carbon of intact thicket. Soil carbon stocks in topsoil were constrained at low concentrations of extractable K (<0.5 mmolc kg−1), Mg (<1 mmolc kg−1), Ca (<12 mmolc kg−1) and extractable P (<40 mg kg−1), suggesting that carbon sequestration will be strongly influenced by soil nutrient content. Restoration of Baviaans Spekboom Thicket stands to sequester 70 ± 8 t ha−1 of below-ground carbon – an amount rivalling sequestration potentials in degraded mesic forests.