23 Mar 2023
The newly published book "Fairy Circles of the Namib Desert" does not provide a sensational new discovery about the bare circles on the eastern edge of the Namib Desert. The riddle of the fairy circles has long been solved, their mystery "disenchanted" years ago. By Norbert Jürgens, the now emeritus professor of biology at the University of Hamburg. With his groundbreaking publication "The Biological Underpinnings of Namib Desert Fairy Circles" from 2013 in the renowned scientific magazine Science.
In less than three pages, Jürgens not only introduced the creator of the circles, the sand termite Psammotermes allocerus. He also explained convincingly what the bare areas serve for: As permanent habitats in an area that receives little and in some years no rain at all. His findings were based on the results of a long-term study in various fairy-circle areas of the Namib. Its publication triggered a broad discussion among scientists. The media also took up the topic.
What makes the now published Fairy Circles book special is its comprehensive and well-founded presentation of this fascinating phenomenon. On 376 pages Norbert Jürgens summarises the scientific discussion, deals with objections, presents further research results and answers detailed questions. In the process, he lets 14 experts have their say, in disciplines such as entomology or soil science.
For the scientific community, the book is written in English and studded with references, source references and references to the results of other researchers. For interested laypersons, it is comprehensibly formulated, richly illustrated (with almost 800 photos, graphs and tables) and attractively presented.
The two target groups also explain the twofold context of the publication: On the one hand, the book appears as the seventh volume in the series Biodiversity & Ecology, for which the Department of Biodiversity, Evolution and Ecology at the Institute of Plant Sciences and Microbiology at the University of Hamburg is responsible. On the other hand, the book is an independent publication of the Klaus Hess Verlag, which specialises in publications about Namibia.
But now to the content. Fairy circles are circular, bare patches in the grass savannah with a diameter of several metres. They are found on sandy soil on the eastern edge of the Namib Desert. In a strip from the south of Angola to the north of South Africa, the average annual rainfall is 50 to 100 mm. The circles are often bordered by a ring of grasses that grow denser and higher than in the surrounding area ("matrix"). Jürgens calls it a luxury belt.
The fairy circles serve as water reservoirs. One should not be deceived by their bare surface and the dryness at the edge of the Namib: At a depth of 60 cm, the sand is moist. The sand termite Psammotermes allocerus [in italics] makes sure of that. It clears the surface of grasses so that the little rainwater can seep away and not be absorbed by the roots of the plants.
This keeps the moisture in the soil, well protected from evaporation, even during years of drought. As soon as enough rain falls, the underground reservoir fills up again.
The water reservoir provides humidity in the termite's nests and tunnels, which the insect needs to survive. It also carries grasses on the edge of the circle through dry periods. These grasses, in turn, serve as a safe food source for the termite in years of drought, when no new grass plants grow due to the lack of rain. Thus, the ring of lush standing grasses is actually not a luxury belt, but an emergency reserve.
There are bare patches that gradually are covered again by young grasses. This is an indication that the termite colony in question has apparently perished. Psammotermes allocerus [in italics] has enemies, including carnivorous ants and the desert-dwelling Golden Mole.
But the "dying" of circles does not happen so often. Jürgens compared decades-old aerial photographs of fairy-circle areas with satellite images from more recent times. There were surprisingly few changes. His conclusion: fairy circles can easily live for several hundred years.
The book is clearly structured in twelve chapters. The phenomenon of fairy circles is systematically defined, located and described in its form. Then follows a brief outline of the history of research. Residues of poisonous plants had been discussed as causes. Grass-cutting termites. Toxic underground gases.
Most persistent was the self-regulation explanation, according to which grasses form the bare patches and thus benefit from their moisture and nutrients. Although Jürgens and other experts already pointed out contradictions in a scientific publication ("Weaknesses in the plant competition hypothesis..." ) in 2015 and scientifically robust evidence is still lacking.
The proponents of this explanation, so-called ecosystem modellers, even recently claimed in the media to have refuted the termite theory (see our report). Their main arguments: in the circles they studied, they had found neither grasses eaten by termites nor the termites themselves.
Of course, Jürgens also addresses this objection: Psammotermes allocerus leads an inconspicuous life. In contrast to its relatives, which build man-sized mounds, it only creates underground tunnels. Probably to avoid the heat of the day, it is only active at night and early in the morning. Traces of its activity above ground can only be seen after one of the rare rainfalls and when looking very closely: Piles of sand about 5 mm "high", which come from cleaning the tunnels and are dispersed by the lightest wind in dry weather.
In the meantime, Norbert Jürgens has data on more than 1,700 fairy circles where Psammotermes allocerus or its tunnel structures have been found. By the way, in his book he also gives tips on how to track down the shy termite. Only this much should be said here: You have to prepare the fairy circle in a certain way in the evening and get up very early the next morning...
Other chapters examine fairy circles in the context of different landscapes, soil conditions and interactions with plants, animals, microorganisms and fungi. Jürgens and his co-authors also expand the view on vegetation patterns in the Namib Desert, which are often mistaken for fairy circles.
The book concludes with a section that seeks to correct the image of the termite as a pest that prevails among many people. Emphasis is placed on their role as ecosystem engineers, contributing to the diversity of living conditions and species in the areas concerned. Termites build up organic carbon in the soil, redistribute nutrients across the landscape and form an important link in the food chains of other animals. Thus, the book is also a plea for termites and their importance for ecosystem functioning and biodiversity in southern Africa.
Norbert Jürgens et al. (2022): Fairy circles of the Namib Desert – Ecosystem engineering by subterranean social insects. Klaus Hess Publishers, Göttingen & Windhoek 2022. 376 pages.
ISBN: 978-3-933117-96-0 (Germany), 978-99916-57-44-8 (Namibia)
The book is available in Gondwana's online shop The Narrative Namibia.
Prof. emeritus Norbert Jürgens has devoted four decades of his research to the study of vegetation in the Namib Desert. Born in Rotenburg (Wümme) in Germany in 1953, he received his PhD from the University of Hamburg in 1986 with a thesis on the evolution and ecology of African drylands.
His research focused on evolution and functional adaptations of plants and ecosystems to the extreme environmental conditions in deserts and savannas. Another topic area was causes of change in biodiversity due to climate change and land use. Based on phylogenetic research and biogeography, Jürgens redefined the floral kingdoms of Africa.
He also coordinated the establishment of international institutions for researching and monitoring global biodiversity, advising on nature conservation and sustainable land use, and combating desertification in Africa and worldwide. He has been emeritus since April 2022. (Source: Wikipedia)
Sven-Eric Stender
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