Spekboom Carbon Sequestration and Rehabilitation Project
In the Eastern Cape Province of South Africa, Subtropical Thicket has faced severe pressure from agriculture. Originally spekboom-dominated thicket covered approximately 1 200 000 ha of which 550 000 ha (46%) is heavily degraded, 450 000 ha (37%) is moderately degraded, and only about 200 000 ha (17%) is intact. Spekboom or Portulacaria afra is highly palatable to many browsers such as elephants and goats. As elephants graze from the top down, small spekboom branches that fall to the ground are able to root and form a new plant and thus ecosystem integrity is maintained. Since the 1930s, commercial farming of goats has decimated spekboom. Goats browse from the bottom up and small plantlets find it difficult to establish. This prevents vegetative spreading and as seeds and seedlings rarely survive or are absent in thicket vegetation, spekboom struggles to recover from browsing by goats.
Spekboom is unusual as it can switch between C3 and CAM photosynthetic pathways. When conditions are moist the plant uses efficient C3 pathways. However when water is limiting, spekboom switches to night-time CO2 fixation through CAM pathways. This allows spekboom to attain high carbon-fixation rates, even under adverse moisture conditions, which naturally influences soil carbon stocks. Soil carbon in the top 30 cm of soil in intact thicket has been measured at 133 t C ha-1. This is very high for a semi-arid ecosystem where water availability often severely limits photosynthesis and carbon fixation and compares favourably with values from tallgrass prairie in Wisconsin (80 – 120 t C ha-1, 0 – 50 cm) and European forests (40 – 193 t C ha-1, 0 – 50 cm). These characteristics of spekboom mean it is an ideal plant for carbon capture which can then be sold on international markets as carbon credits under the voluntary carbon standard mechanism. In 2011, a carbon sequestration project was registered by the Department of Environmental Affairs in partnership with the Development Bank of South Africa, Eastern Cape Parks Tourism Authority, and South African National Parks. The carbon sequestration project is based on the restoration of spekboom thicket and verified projections of the carbon sequestered in the soil which can then be sold on the international carbon markets. Benefits from the project include recovery of ecosystem services, and job creation in impoverished rural communities through the labour intensive restoration phases.
Source of funding
Clarke, C.L., Shackleton, S.E., Powell, M., 2012. Climate change perceptions, drought responses and views on carbon farming amongst commercial livestock and game farmers in the semiarid Great Fish River Valley, Eastern Cape province, South Africa. African Journal of Range and Forage Science 29, 13-23.
Cowling, R.M., Mills, A.J., 2011. A preliminary assessment of rain throughfall beneath Portulacaria afra canopy in subtropical thicket and its implications for soil carbon stocks. South African Journal of Botany 77, 236-240.
Mills, A., Fey, M., 2004. Transformation of thicket to savanna reduces soil quality in the Eastern Cape, South Africa. Plant and Soil 265, 153-163.
Mills, A., 2008. Eastern Cape Thicket Restoration Project: History and next steps. Carbon Standards Workshop for South African Climate Change Biodiversity projects. http://www.cap.org.za/workshop_01/session_4/Anthony%20Mills_R3G_E%20Cape%20restoration_session%204.pdf. Accessed 14-12-2013.
Mills, A.J., Cowling, R.M., 2010. Below-ground carbon stocks in intact and transformed subtropical thicket landscapes in semi-arid South Africa. Journal of Arid Environments 74, 93-100.
Mills, A.J., Cowling, R.M., Fey, M.V., Kerley, G.I.H., Donaldson, J.S., Lechmere-Oertel, R.G., Sigwela, A.M., Skowno, A.L., Rundel, P., 2005. Effects of goat pastoralism on ecosystem carbon storage in semiarid thicket, Eastern Cape, South Africa. Austral Ecology 30, 797-804.
Mills, A.J., Cowling, R.M., Steyn, D., Spekreijse, J., Van den Broeck, D., Weel, S., Boogerd, C., 2011. Portulacaria afra is constrained under extreme soil conditions in the Fish River Reserve, Eastern Cape, South Africa. South African Journal of Botany 77, 782-786.
Mills, A.J., Turpie, J.K., Cowling, R.M., Marais, C., Kerley, G.I.H., Lechmere-Oertel, R.G., Sigwela, A.M.,
Powell, M., Mills, A. And Marais, C., Carbon Sequestration and Restoration: Challenges and Opportunities in Subtropical thicket. http://www.nda.agric.za/doaDev/sideMenu/ForestryWeb/webapp/ResourceCentre/Documents/Reports/4271___Day2_session3_item1.pdf. Accessed 14-12-2013
Powell, M., 2007. Assessing Costs, Benefits, and Feasibility of Restoring Natural Capital in Subtropical Thicket in South Africa, in: Aronson, J., Milton, S.J., Blignaut, J.N. (Eds.), Restoring Natural Capital: Science, Business, and Practice. Island Press, Washington, pp. 179 - 187.
Van der Vyver, M.L., Cowling, R.M., Campbell, E.E., Difford, M., 2012. Active restoration of woody canopy dominants in degraded South African semi-arid thicket is neither ecologically nor economically feasible. Applied Vegetation Science 15, 26-34.
van der Vyver, M.L., Cowling, R.M., Mills, A.J., Difford, M., 2013. Spontaneous return of biodiversity in restored subtropical thicket: Portulacaria afra as an ecosystem engineer. Restoration Ecology 21, 736-744.
van Luijk, G., Cowling, R.M., Riksen, M.J.P.M., Glenday, J., 2013. Hydrological implications of desertification: Degradation of South African semi-arid subtropical thicket. Journal of Arid Environments 91, 14-21.