Once considered just an ornamental bonsai plant outside of its home range of South Africa, the shrub Portulacaria afra, commonly called “spekboom,” is garnering attention for its carbon storage capabilities. Native to the arid cape region of South Africa, spekboom thickets can store 20 kilograms of carbon in every square meter of vegetation, or 200 tons of carbon per hectare. That’s equivalent to taking 37 cars off the road for a year. Since most dryland areas similar to the cape store less than 50 metric tons of carbon per hectare and deciduous forests are estimated to store 120 metric tons per hectare, this nearly 8-foot-tall plant could be a key to future carbon-capture trading markets in arid regions.
Unlike many arid plants, when soils are dry, speckboom can switch from the photosynthetic process that most plants in the world use to a less common and water-conserving photosynthesis pathway called “CAM.” Because of this, the carbon sequestration process in the plant is highly efficient for its environment, allowing it to thrive on only 10-11 inches (250-350 millimeters) of rain a year. Researchers also believe spekboom’s umbrella-shaped canopy allows organic material to accumulate at the base of the shrub, improving the water-holding capacity of the soil below.
Whether planting spekboom thicket plantations outside South Africa will be feasible remains to be seen, but it one day it could be a water-efficient way for regions like the Southwest United States to enter the emerging global carbon market.
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