Vegetation at Drie Kuilen
Drie Kuilen Nature Reserve has three unique and notable vegetation types:
- Matjiesfontein Shale Renosterveld
- North Langeberg Sandstone Fynbos
- South Langeberg Sandstone Fynbos
There are also good examples of heuweltjies – a class of soil surface feature that occurs widely in the south-western Cape of South Africa.
One theory is that heuweltjies are fossil termite mounds. Within this hypothesis, there are two conflicting opinions on the origins of heuweltjies, one maintaining that heuweltjies were built by the harvester termite (Microhodotermes viator), the other that heuweltjies were built by a now possibly extinct termite species. The earliest radiocarbon dates on heuweltjies suggest an age of about 30,000 or even 40,000 B.P.
Another theory is that heuweltjies are created by burrowing (fossorial) animals. Variants of this hypothesis are that the animals are mole-rats in the families Bathyergidae and Rhizomyinae; termites; or a combination of mole-rats and termites. A further theory is that heuweltjies are caused by differential erosion in places where the availability of water limits the growth of vegetation, creating natural patterns such as tiger bush. Scientists note that heuweltjies contain at least ten times more soil than any termite nests in South Africa, and that they can occur on bedrock, which termites could not be tunnelling through to move soil upwards. Further, the heuweltjies had the same spatial distribution as bush-clumps, patches of woody vegetation forming patterns. They suggest that heuweltjies formed from bush-clumps as these protected the soil from eroding away, producing calcrete hardpans.