Salvadora and the Strange Oasis

We drove northwards, surrounded by a vastness of water and sand, the Atlantic Ocean to the west, the Namib Desert to the east. After a couple of hours, rocky outcrops, previously hazy in the distance, came into focus; the Brandberg and surrounding mountains rose sharply from the plains. The sky was filled with low-lying clouds and a cold wind blew fog inland from the ocean. The sun had begun its descent several hours prior and the stark, blackened mountains stood ominously in the dimming light. Eventually, we turned off the main coastal road and trundled down a dusty, corrugated track heading towards the mountains. The track veered around the dry ephemeral Messum River channel, bordered by precipitous rock shelves sculpted by millennia of erosion. The track, enclosed by the walls of crumbling rock, eventually opened out into a desolate expanse. We had entered the caldera of the Messum Crater, an extinct supervolcano some 18 kilometres in diameter, last active 130 million years ago. Dotted around the surrounding desolation stood thousands of Welwitschia plants, barely visible in the dim evening light. The ringing sound of silence filled my ears. This foreboding landscape exuded a primaeval air that instilled pure wonderment.

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.

Walking down the sandy Kuiseb riverbed I would often hear rustling coming from within the dense, tangled Salvadora bushes. I wondered what creatures could be lurking there. African wildcats and brown hyenas have been spotted along the Kuiseb River in the central Namib and may shelter in the larger bushes; jackals and foxes probably use Salvadora for shelter during the day too. Snakes, geckos, spiders and scorpions almost certainly reside within, not to mention countless insects. Accidently I even frightened off a small antelope one day, which was in a large Salvadora bush seeking respite from the sun. The invisible water was supporting plant life in one of the driest places on earth, which in turn sustained countless creatures. I began to think of Salvadora from the perspective of a small animal, as a sprawling biological metropolis literally buzzing with life.

So how does all of this relate to the damp termite soil dumps in the Messum Crater?

I decided to develop this idea of a ‘biological metropolis’, mixing art with science into a short film. As I spent more time in and around Salvadora bushes I began to notice that the harvester termite, Hodotermes mossambicus, was more likely to be seen foraging detritus from Salvadora than anywhere else in the vicinity. Harvester termites, as their name suggests, harvest organic matter, in this case, small pieces of Salvadora twigs and leaves. The workers drag the twigs, which are often far larger than their own bodies, back to their nests using their powerful jaws and then store the plant matter underground for use as food. Colonies can be gigantic. I once observed thousands foraging under a Salvadora bush: the sheer quantity of the tiny insects produced an audible rustling.

One day in the Kuiseb I noticed the same damp termite soil dumps that Professor Turner had pointed out in the Messum Crater. This time hundreds of tiny flies, barely visible, were crowded on top of the damp mounds. They were drinking. I began to notice this frequently as I spent more time around Salvadora, not just with flies but other insects too. Dune ants, Camponotus detritus, and the Zophosis moralesi beetles would become transfixed on the damp soil, thirstily guzzling all available moisture. The termites were providing a way for other insects to access the otherwise unobtainable underground water. As long as the termites continued to expand their underground nests, fresh damp soil would often appear above ground and other insects would take advantage of this. These were termite-constructed oases.

Thanks to the digging termites, other insects in the central Namib quench their thirst with rain that fell hundreds of kilometres away. Combinations of seemingly unrelated events and organisms have come together to allow access to moisture in a hyper-arid desert environment. My observation of this interaction, not previously documented in the Namib, stemmed from the seemingly trivial patches of damp soil in the Messum Crater. Considering how numerous harvester termites are along the Kuiseb River, this poses the question of how valuable these termite-constructed oases are for insects, and it confirms that desert organisms are willing to exploit any convenient source of moisture. No matter how seemingly inconsequential, the scientific value of observation is crucial to advancing our knowledge and understanding of the world around us.

If we are to put ourselves into the figurative shoes of the wandering beetle, these mounds of damp soil are no longer unremarkable. They are instead a welcome, refreshing respite. What initially may appear insignificant is often revealed to be astonishing upon closer inspection. Wonders are often found within the subtleties of life. All we have to do is look.

This interaction and behaviour can be found, described and filmed for the first time, in the short film Salvadora, available to watch online for free on the writer’s website. 

You might also enjoy reading: Namibia’s National Parks: Where Do All the Skeletons Come From?

This article was first published in the Spring 2018 edition of TNN.