On a national scale Mucina and Rutherford (2006) recognise 63 vegetation types in the Succulent Karoo biome. Five of these vegetation types (Western Little Karoo, Western Gwarrieveld, Little Karoo Quartz Vygieveld, Eastern Little Karoo, and Prince Albert Succulent Karoo) are endemic to the biosphere reserve. The biosphere reserve thus plays a vital role in protecting an important component of this biodiversity hotspot.
When viewed at a much finer scale, the complexity of the local Succulent Karoo becomes clear. A total of 94 vegetation units are recognised in the Succulent Karoo of the biosphere reserve. All of these finer-scale units are endemic to the biosphere reserve and many are threatened.
No comprehensive checklist is available of the flora or fauna that are present or endemic to the Succulent Karoo in the biosphere reserve.
Abundant and characteristic plant families are the Asphodelaceae, Aizoaceae, AsteraceaeCrassulaceae and Euphorbiaceae. Of the Asphodelaceae, most of the members of the genus Haworthia present in the area are endemic. In the Aizoaceae five of the genera (Antegibbaeum, Bijlia, Octopoma, Smicrostigma and Zeuktophyllum) and almost all the species in the genera Gibbaeum and Glottiphyllum, are endemic to the biosphere reserve. Several of the Asteraceae, notably in the genus Euryops, are rare and localised endemic species. There are a number of endemic Crassula and Euphorbia species and many of the Iridaceae present, especially species of the genus Moraea, are also endemic to the Succulent Karoo vegetation in the biosphere reserve.
Four tortoise species occur in the local Succulent Karoo vegetation, but none of them are endemic to the biosphere reserve. Very little is known about the invertebrates of the area, but some of the Stone grasshoppers (genus Trachypetrella) and Jewel beetles (genus Julodis) are probably rare endemic species.
Two of the many rare species endemic to the Succulent Karoo, Haworthia emelyae and Euphorbia pseudoglobosa (Photos: Jan Vlok).
Important natural processes:
A feature of the Succulent Karoo is the occurrence of “Heuweltjies”, ancient termitaria thousands of years old that function as nutritional hotspots for fauna. These termitaria are prone to overgrazing by domestic stock, and once heavily disturbed will collapse and cause soil erosion.
The lowland “Gannaveld” vegetation type acts as an important area for the natural deposition of soils and nutrients in the landscape. It is often used for intensive ostrich farming, causing severe damage to the vegetation, soil erosion and nitrification of the local river systems. The deep soft soils of “Gannaveld” are also an important nesting habitat for wasps and tortoises.
One of the most important disturbance regimes is grazing by small resident game species, but also some larger game species that probably migrated seasonally through the different vegetation types of the biosphere reserve.
The tortoises probably acted as important seed dispersal agents for many of the highly localised Aizoaceae species that are restricted to islands of quartz outcrops.
The abundance of Aloe species is an important source of nectar to bees and nectivores during winter months.
Unfortunately none of the above aspects have been studied in detail, so only general notes on these ecological processes are provided.
Main human impacts:
The establishment of irrigated agricultural lands on the deep soils of the lowlands has altered much of the natural vegetation and aquatic systems of the Succulent Karoo as water is largely abstracted from the adjacent rivers to irrigate these lands.
The ostrich industry is well developed in the region and has had a negative impact on many Succulent Karoo vegetation types as these large birds cause immense damage to the vegetation.
The emerging game industry, which has largely replaced original stock farming in the area, holds a dire threat as landowners introduce extra-limital game species and erect many game fences that act as a barrier for the migration of indigenous species.
Undue expansion of urban areas in this arid system holds a threat as almost all the available aboveground water resources have already been exploited and further development depends on abstraction from deep aquifers. This has already resulted in lowering of the water table and the drying up of many natural springs.
Relevant management practices:
- Inform private landowners who own important remnant patches of endangered Succulent Karoo vegetation types about the occurrence of these sites and support them to protect them.
- Remove alien plant infestations from the river systems.
- Restrict ostrich industry to already disturbed land.
- Engage with emerging game industry to ensure that only indigenous game species are introduced and maintained at sustainable levels. Stimulate collaboration between adjacent landowners to ensure that game fences are kept to a minimum.
Support eco-friendly tourism ventures that can act as motivation for landowners to protect remnant patches of threatened vegetation types.