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Keywords:

  • biomass;
  • carbon sequestration;
  • Portulacaria afra;
  • restoration;
  • semiarid landscapes;
  • soil carbon;
  • thicket

Abstract

Ecosystem carbon storage in intact thicket in the Eastern Cape, South Africa exceeds 20 kg/m2, which is an unusually large amount for a semiarid ecosystem. Heavy browsing by goats transforms the thicket into an open savanna and can result in carbon losses greater than 8.5 kg/m2. Restoration of thicket using cuttings of the dominant succulent shrub Portulacaria afra could return biodiversity to the transformed landscape, earn carbon credits on international markets, reduce soil erosion, increase wildlife carrying capacity, improve water infiltration and retention, and provide employment to rural communities. Carbon storage in two thicket restoration sites was investigated to determine potential rates of carbon sequestration. At the farm Krompoort, near Kirkwood, 11 kg C/m2 was sequestered over 27 years (average rate of 0.42 ± 0.08 kg C m−2 yr−1). In the Andries Vosloo Kudu Nature Reserve, near Grahamstown, approximately 2.5 kg C/m2 was sequestered over 20 years (0.12 ± 0.03 kg C m−2 yr−1). Slower sequestration in the Kudu Reserve was ascribed to browsing by black rhinoceros and other herbivores, a shallower soil and greater stone volumes. Planting density and P. afra genotype appeared to affect sequestration at Krompoort. Closely-packed P. afra planting may create a positive feedback through increased infiltration of rainwater. The rate of sequestration at Krompoort is comparable to many temperate and tropical forests. Potential earnings through carbon credits are likely to rival forest-planting schemes, but costs are likely to be less due to the ease of planting cuttings, as opposed to propagating forest saplings.