In early 2017, I had the privilege of camping in the Messum Crater with several knowledgeable and inspirational scientists. The Messum Crater, a harsh environment, unforgiving and remote, is one of the less visited, yet accessible parts of the Namib Desert. Its eponym is Captain William Messum, who travelled across this land from the ocean at Cape Cross around 1850. The Messum Crater has numerous archaeological sites, rock paintings and many Welwitschia plants, living fossils that date back some 200 million years. Being here was the closest I have come to travelling through time to some distant prehistoric era. Despite my veneration of this bygone landscape, the result of this excursion shifted my focus from the past to a novel observation.
At our campsite, on the second morning of our stay in the Messum Crater, J Scott Turner, a professor of biology from the State University of New York College of Environmental Science and Forestry (USA), pointed out to us some small mounds of soil, several centimetres high. “These are soil dumps created by termites”, explained Professor Turner. Harvester termites construct vast subterranean nests with tunnels that lead to the surface; excess soil gets dumped above ground resulting in these miniature mounds. However, these soil dumps were damp. The termites had dug deep enough for their nest to reach underground water. This may seem surprising in a place as arid as the Namib, but we were in the vicinity of the Messum River which, despite being dry at the time, indicated the presence of underground water from past flow. As we continued into the Messum Crater and beyond, I put Professor Turner’s observation to the back of my mind. It would soon surface again, however.
At the time of our Messum Crater visit, I was based at the Gobabeb Research and Training Centre, a few hundred kilometres south of Messum in the Namib-Naukluft Park. Gobabeb is located on the Kuiseb River in the central Namib Desert.
The Kuiseb, much like the Messum River and most other Namibian rivers, is ephemeral and dry most of the time. The Kuiseb rises in the Khomas Hochland region, near the capital of Windhoek, and runs in a south-westerly direction into the heart of the Namib Desert. Gobabeb rarely sees water flooding this dusty channel. The river only flows this far when enough rain falls hundreds of kilometres away in the catchment area in the interior. In the sun-soaked central Namib, the Kuiseb can go from flooded to dry in a matter of days, with much of the water seeping into the sandy surface and resting in an aquifer. This is why we see mass vegetation along the dry Kuiseb River channel in the middle of the desert; roots of trees extend deep under the surface to extract the water.
There is a plant found along parts of the Kuiseb that intrigued me from the start. I remember asking if it was an invasive species (a plant not native to the area, but introduced, which can have a detrimental effect on native wildlife and/or cause economic damage). It wound around the trees, seemingly choking them with its grasp of intertwining branches and bushy leaves. Its green leaves were relatively large, unusual for desert-adapted plants, which mostly have small leaves or none at all. For plants with roots capable of reaching the underground water, however, this was an oasis.
The plant in question was indeed native to this area but it is also found in many other African countries, parts of Saudi Arabia and India. It was Salvadora persica, which goes by many common names such as miswak and arak in Arabia, or the mustard bush or toothbrush tree because its twigs can be used as a natural toothbrush. Much research has been conducted on the chemical properties of the plant, with results showing that it really is beneficial for oral health and dental hygiene. The dental benefits of the plant have been known for generations and are acclaimed in a poem written by Suwayd ibn Abi Kahil al-Yashkuri in the 17th century A.D.