BOTANICAL ENCOUNTERS: Rewilding In Southern Africa - The Kalahari Dunes
- k-england
- Jun 1
- 7 min read
Words and pictures by Ida K. Rigby, for Let’s Talk Plants! June 2025.
Rewilding In Southern Africa - The Kalahari Dunes
The Kalahari Desert covers 350,000 square miles in parts of South Africa and Namibia and most of Botswana. At its north-south longest, the Kalahari is 1,000 miles and its greatest east-west distance is about 600 miles. (britannica.com)
The shelf of sand that is the Kalahari is about 200 feet deep and at an altitude of 3,000 feet. The sands are low in organic matter, relatively alkaline and dry. “Kalahari” comes from the Tswana Kgala for “great thirst” or Kgalagadi, “the waterless place.” The Kalahari has a variety of ecosystems. In previous columns we have explored its northern savanna consisting of acacias,...
... dense mopane woodlands, ...
...palms ...
...and baobabs.
The Okavango Delta...
...is a flat swamp part of the year until the flood waters from Angola sink into the sand.
The sand sheets in the southern areas can only support trees with deep roots. Shallow-rooted perennial grasses grow after a rain and reseed.
Tswalu Kalahari is in the southwestern part of the Kalahari.
Our last column, on rewilding at Tswalu, was centered on the restoration of the flat plains.
Tswalu’s red sands (iron oxide coated grains) are the perfect habitat for the irresistible meerkats (any excuse to show some meerkat photos will do).
Tswalu is known for guests being able to visit a habituated colony. The colonies are habituated by a young woman who spends months quietly acclimatizing them to a human presence. When the sun crests a nearby mountain and shines on the colony, one member emerges to check for raptors, snakes, and weather conditions.
If the report is good, others emerge.
Meerkats are ever wary and constantly scanning for predators as they sun themselves before heading out to hunt before it gets too hot.
These plains are hot, even in winter, so creatures adapt. This squirrel uses its tail as a sun umbrella.
The western Kalahari’s dunes are longitudinal dunes at least one mile in length, several hundred feet in width and 20 -200 feet in height and separated from one another by a broad depression locally called a street or lane because it constitutes an easy way to travel. (britannica.com) Most of us think of dunes as the massive, ever-shifting structures at Sossusvlei in Namibia, which devour trees and shrubs in their path ...
... and are sparsely vegetated, if at all,...
or those of the Sahara in Morocco.
The Kalahari dunes at Tswalu are stable dunes, but many had lost their stabilizing crest cover to over-utilization by ranchers; they are regrowing their stabilizing plant covers.
Conrad Geldenhuys’s “Kalahari Dunes: Can the Kalahari’s new wig cover up the truth?” (pza.sanbi.org) is a fascinating account of the results of over-utilization.
Even native plants, such as Kalahari sour grass, can become dominant, creating dense monostands as other smaller grasses, such as gha grass, Centrpodia
glauca, tall Bushman grass, Stipagrostis ciliate, and small Bushman grass,
Stipagrostis obtuse, and shrubs are eliminated by over-grazing. If the denuded dunes reach a tipping point they “reawaken.”
“Without grasses to anchor the dunes in place, their sand grains are blowing in the wind.” (Cheryl Dybas, “Sleeping sands of the Kalahari awaken after more than 10,000 years,” phys.org)
According to Dybas, the last time Kalahari dunes were on the move was more than 10,000 years ago; they started moving again in just the last three to four decades. This can be attributed to boreholes, the water from which allows for year round grazing in arid areas once used only in wet years by ever larger domestic herds. With the degradation of the dunes, the grasses disappear and the winds no longer blow across the grasses, but across the sand and disperse the grains. What were vegetated, fixed linear dunes reach a tipping point and can become “barren and active dunes.”
The dune Bushman grass, Stipagrostis amabilis, covers healthy Kalahari dune crests. It’s tough, relatively unpalatable and shields other species from the windy and abrasive conditions prevailing on the dune crests (Dybas). Dune reed indirectly maintains the seed bank for other species on the dune crest. As ranchers over-utilize the dune valleys and slopes they become depleted and game and livestock move to the dune crests to graze. Even the dune reed on the crests are grazed and start to decline. The resultant bare, lifeless dunes flatten out to form table tops due to the scouring winds. Dybas notes that sites like these prove very difficult to rehabilitate.
The dunes at Tswalu illustrate how Kalahari dunes can recuperate from over utilization. Some dunes at Tswalu still have the bare sides and crests indicative of their former lives as farms and ranches before Tswalu purchased them.
Some show grasses, shrubs and trees beginning to return.
Some have achieved a stable restoration of the flora that will stabilize the dunes.
This photo...
...shows the restoration of the sand sheet plain with acacia trees again supporting weaver birds, and native trees and shrubs offering browse and shade to giraffes and kudus. In the distance is a stabilized dune with mature trees, shrubs and seasonal grasses.
One morning in 2014 our guide shadowed a lion pride en route to a water hole.
The night before one of the young males in the pride had been killed by a male lion. Tswalu manages the animal populations so that such natural interactions can occur. The lion prides are in a large, securely fenced area so they do not go into local villages. As we followed, the pride descended a dune to the water hole...
...and drank.
The lions then climbed up to the other side of the dune to rest during the heat of the day.
When I was there in 2019, it was time to replace the dominant male brothers in one of the lion prides so as to avoid their mating with their daughters (a potential problem in a limited area where the males cannot widely disperse) so new, relocated males were in a quarantine facility. The two dominant males were aware of their roaring and were waiting outside to meet the challenge.
When the new males would be released there would be a fight. The result (which I do not know) would have been either the death or maiming of the older lions or their retreat and giving up their pride.
The dunes also are the perfect site for Tswalu’s packs of African painted wolves (African wild dogs) to excavate a hidden den. Here we see the pack, including the puppies, returning to their den, including the puppies, who were allowed to join the adults at the site of a kill.
This dune is well stabilized by the reestablished grasses and a few shrubs. This pack died out two years later due to distemper contracted during an escape from Tswalu into a local village.
While we were waiting for a rare sighting (one of the guides had, early in the morning, seen a pangolin enter a burrow and would radio us when it emerged), we explored the top of a nearby dune. Pangolins are opportunistic in their choice of a den for the evening, so it was chance that it had been seen entering a burrow. Our guide, eyes shining, stopped and gestured towards the base of a tree.
Bunny?
No, it was the very animal I had asked him to try to find when we first met. Yes, an aardvark!
Tswalu is known for the potential for seeing aardvarks, but I had not seen one on my visit in 2014. The aardvark was excavating next to a tree for harvester termites.
They feed on ants and termites.
I had not seen them in 2014 partially because they are mostly nocturnal in order to avoid overheating, but also due to a drought. In her PhD thesis abstract of her study of aardvarks at Tswalu, Nora Marie Weyer explains that they are “ecological engineers because they dig the burrows that provide shelter for numerous sympatric [overlapping in distribution] animals and, as such, are keystone mammals in sub-Saharan Africa. They are nocturnally active, solitary and elusive. . . “ (tswalu.com) The drought in 2012-13 caused a decline in termites and therefore high aardvark mortality, which may in part explain why I did not see one in 2014. The longer-term concern is that the Kalahari semi desert (where Tswalu is located) at the south-western edge of aardvark distribution is the hottest and driest environment currently inhabited by aardvarks. According to Weyer, climate change will likely exacerbate the Kalahari’s harsh conditions. How or if aardvarks will be able to adapt is unknown. While we watched, the aardvark ambled off through the trees, shrubs, and grasses of the stable dune crest.
Another treat was in store for us; we got the call that the pangolin had emerged for its evening hunt.
The research of another PhD student at University of Witwatersand, Wendy Paniono, who studied the Temminck’s ground pangolins at Tswalu, focuses on the effects of climate change on pangolins and their prey. (tswalu.com) They are “incredibly fussy eaters; their highly specialized diet focuses on specific ants and termites. . . . hotter and drier conditions reduce the availability of those insects, and pangolins do not seem to be able to shift their diet to other possible food sources (as bat-eared foxes can do, for example). . . Pangolins that do not have enough food to keep themselves warm during the cold night can shift their activity to the warmer daytime, . . . but climate change is resulting in those days becoming much hotter.” Paniono’s findings showed that these pangolins experience a rapid rise in body temperature when exposed to daytime heat. She concludes that pangolins are “already walking a tightrope, trying to balance food intake with maintaining a normal body temperature.”
Hopefully, the successful restoration of the ecology and geology of the Kalahari dunes at Tswalu shows how nature can heal itself and recover.
The Tswalu Foundation funds research on which to base the management of the reserve in order to achieve this goal.
Ida Rigby is a past SDHS Board member and Garden Tour Coordinator. She has gardened in Poway since l992 and
emphasizes plants from the northern and southern Mediterranean latitudes. Her garden received the San Diego Home/Garden magazine Best Homeowner Design and Grand Prize in their Garden of the Year contest in l998. Her travels focus on natural history.
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