People travel from far to see iconic elephants, rhinos and lions in Ongava – three of the Big Five. Ecologists laud these animals for being ecosystem engineers. But how do these bulky animals that aren’t much good at surviving compare to our real, big heroes: Ongava’s fairies. They are the largest, oldest and most interesting of them all, not least because no one has seen a fairy, yet! But their fairy ring footprints are everywhere, and they do more to engineer the environment than anyone else. Only something so enigmatic as fairies could make these rings, or so we like the story to be told. They are also extremely good survivors, as I found by asking two simple questions: how long they have been there, and for how long may they persist?
Fairy rings are bare patches of ground around old termite mounds, as distinct from the well-known fairy circles of the Namib. With diameters of between 10 and 40 metres, the rings are easy to see and count. Number M22 viewed on the ground (left) and from an overlooking dolomite ridge (right). M22 is plainly visible in the next image taken from a satellite in May 2023, as in the Google Earth image below. It was also visible in an aerial photo taken 62 years previously in July 1961.
Part of Ongava where fairy rings were counted. Those marked with yellow dots were visible in 1961 and 2023. The cyan dots show places where rings were present in 1961 but had disappeared by 2023, while red dots mark newer rings that appeared between 1961 and 2023. The green arrow marks the location of M22 shown in the photos above. The white arrow points to the fairy ring at the centre of the red circles in the inset images for 1961 and 2023 below.
To estimate their ages and potential longevity, I counted all the rings within an area of 660 hectares of Ongava Game Reserve in 1961 and in 2023. Of the 227 rings counted there in 1961, 149 were still present in 2023. The other 78 rings had disappeared at an annual ‘mortality’ rate of 0.68% during the passage of 62 years. Extrapolating that rate into the future would indicate that the last of the fairy rings present in 1961 should disappear in the late 28th century, about 750 years from now.
Eighty-six new rings appeared between 1961 and 2023, giving us a total of 235 rings in the 660 hectares in 2023, and so a few more new rings were formed than the 78 lost between 1961 and 2023.
An important point: the ages mentioned here are periods when termite mounds are surrounded by large aprons of bare ground. The mounds are then active or – more usually – deserted. And those that are still active are certainly old. How old? I’d imagine a few decades, since its takes termites years to build the colossal mounds from soil collected – grain by grain – below ground, and the mounds are then probably occupied for decades. It is the soil eroding off mounds that then spreads out as aprons. The original mounds or their footprints are normally visible as dark spots in the centre of each ring. The dark footprints are visible both on the ground and in satellite images.
The fairy rings and termite mounds described here are made by termites of the species Macrotermes michaelseni. Their tall mounds tower over large parts of southern Africa, and in many areas the mounds and their remains are surrounded by bare rings. While the rates at which the rings appear and disappear probably change periodically, termite mounds certainly affect large areas over very long periods. For much of time, they prevent the growth of grasses, shrubs and trees, but for short periods after rain the fresh, nutritious grasses grow there. These attract grazing antelope, rhino and smaller animals which use game trails to walk from one ring to another. For example, I have estimated the rings could provide over 6,000 hectares of nutritious grazing in over 330,000 spheres in Etosha.
By now we should agree that fairy rings are an important part of our landscapes. I am but a curious naturalist doing his simple best to question, to ponder, and to question again. But the big puzzle remains - how do termites or the building of their mounds affect the surrounding soil to such an extent that it remains devoid of most plants over decades and even centuries? This is not an esoteric, academic question. Solving this puzzle will elevate our understanding of processes that control the abundance and health of plants. That will be one great gain. And that answer could lead to innovations to regulate bush encroachment, and to limit other invasive plants and unwanted weeds, for example. Indeed, the development of such natural herbicides could bring significant benefits to humankind, and credit to wise investors who understand the potential value of knowing more about such curiosities as fairy rings.