Mystery of Australia’s desert circles revealed
Near Kintore in the Northern Territory. What causes the circles and their pattern? Image: Tibor Hegedis
Australian Aboriginal people have long used them as sitting areas, walking paths, and places to grind grasses or make artefacts.
In fact, they have names in Aboriginal languages. In Manjilyjarra language they call them linyi.
These grass-fringed, bare, circular patches are widespread in the spinifex desert grasslands of Western Australia (WA) and the Northern Territory (NT). Similar-looking circles occur in Africa and have been the subject of feverish curiosity in international media in recent years. From The Atlantic to the BBC, the media has speculated about this ecological mystery dubbed ‘fairy circles’.
Fungus, gases, plant/water organisation, termites and even dragons have been posited as the cause of the bare circles.
The latest research published in a letter in the Proceedings of the National Academy of Sciences of the USA (PNAS) presents evidence that in the Australian landscape, it’s termites; countering a paper published in PNAS in March.
Excavating the evidence
The research team examined circles in four locations across WA and NT.
CSIRO’s Dr Fiona Walsh and colleagues from WA and the NT, Ashley Sparrow (CSIRO), Peter Kendrick (Dept Parks and Wildlife) and Josef Schofield (Australian Wildlife Conservancy), examined circles on satellite images and then in the field across 1,200 km from Newman in WA to Newhaven Sanctuary in the NT.
Excavations of circles at four locations revealed all circles had concreted soil and chambers made by termites of the genus Drepanotermes, whereas digging away from the circles revealed no evidence of termites.
Soldier termites came to defend their termitaria. Image: Fiona Walsh
At one location, of the ten circles they excavated, 60 per cent of the ‘pavement termitaria’ were active, containing living termites and termite food stores.
AS the letter in PNAS states: Although we accept that water redistribution occurs between bare and vegetated areas in Australian desert grasslands, we have evidence that bare patches are subterranean termitaria, both active and inactive (abandoned).
Pavements are very hard, withstanding fire, flood, and road grader blades; on worn-down vehicle tracks, the termitaria stand as discrete walled structures. Termitaria appear long-lived even when periodically or permanently abandoned; such “ghosts of termitaria” may persist for decades or longer.
Collaborating across culture and science
Dr Walsh said her investigations with other Australian ecologists revealed what desert Aboriginal people have recognised for generations.
The circles were clear of prickly spinifex, so people could sit comfortably on them, she said, and people preferentially walked across them when travelling through the desert. Aboriginal people also swept the circular hard spots as a place to prepare foods and artefacts. Older desert people recognised these spots as a ‘normal’ feature made by termites – “as ubiquitous to them as footpath pavements are to a city-dweller”.
Dr Walsh worked with Gladys Bidu, a Kanyirninpa Jukurrpa ranger, who said pavement termites played an important role in food webs and known desert ecology.
And these linyi are a favoured place for termite-foraging bilbies and echidnas.
Echidna tracks lead to a pavement where the animal has burrowed for termites.
“It is a linyji. Hard parna (ground) made by manyjurrpa, white ants (termites),” Ms Bidu said.
“Linyji is hard and flat like a claypan made by water. But they are made by manyjurrpa so different to a claypan. Ninu or Mankarr (bilby) go to the linyji to get their food. Mankarr dig linyji to eat white ants and pinga (black ants). That’s their food. Porcupine (echidna) dig the linyji too. Porcupine are looking for manyjurrpa too. White ants are their food too. ”
Dr Walsh said their research highlighted the value of Aboriginal and local people’s knowledge.
Gladys Bidu and Dr Fiona Walsh have brought Aboriginal and ecological knowledge together. Image: Sophie Walter
“Scientists are interested in these plant patterns because they tell us about forces that shape plant communities and their distribution, and so help to inform projections of how desert ecosystems may respond to climate shifts and other aspects of global change,” she said.
“A deeper message from our findings is that Australian deserts are so inherently complex, variable and unpredictable that the best people to ask about how these ecosystems work may be local people.”
Dr Walsh said this research raised many ecological and cultural questions relevant to the functioning of desert grasslands and the roles of people and termites within them.
For more, view Seeing the Spots, Re-connecting the Dots, a science photo essay on people and termitaria in the Western Desert.
September 12, 2016 at 9:40 am
Maybe read on a little…… PNAS also published a response to the Walsh et al paper “Reply to Walsh et al.: Hexagonal patterns of Australian fairy circles develop without correlation to termitaria”, doi: 10.1073/pnas.1611877113.
September 12, 2016 at 9:54 pm
Very interesting…. i have followed this issue for a number of years… i am Aboriginal Elder from Anaiwon in NSW ….worked all over Australia in variious roles in Indigenous Affairs..have a keen interest in archaeology.. am custodian of rock art and site in the ranges at Moonbi NSW….
September 15, 2016 at 12:44 pm
Yes, according to usual PNAS practice, Getzin and colleagues have been given the right of reply. Dr Sparrow said: “In their reply, they suggest that we believe that the circles are the eroded bases of termite mounds. What we found is this genus of termites build wide, flat termitaria that are level with the soil surface. They have small, low mounds and sometimes there appear to be no mounds at all. Secondly, we are aware of the processes leading to banded mulga and other demonstrably self-organised vegetation types, but in this case we simply believe that termites are the primary cause rather than plant self-organisation.”
September 20, 2016 at 7:13 pm
What an incredible an interesting land we share,am so pleased to hear the oldest know living people are being heard an their knowledge of this land listened to. Thank-you.
September 22, 2016 at 10:38 am
The termites eat the spinifex hence the circles.
October 17, 2020 at 5:32 pm
Termites eat dead leaves, not live. In the Kimberley termites build mounds in the centre of spinifex hummocks and perhaps use the dead leaves as food and the structure as a framework. But they don’t eat the live spinifex from what I have observed.
September 26, 2016 at 3:42 pm
So pleased all the knowledge of our ancient land is not lost. Keep up your good work.
November 14, 2016 at 2:31 pm
I travelled with Dr John Read to APY Lands SA last year, I remember him stopping the car walking out and lying on the ground with a camera. This part of Australia has a Buffel grass problem and the place which interested John was an area unusually bare of the grass. Getting back into the car he explained he thought the bare area was due to termites. It would be great for APY communities if termites were able to control buffel.
December 5, 2016 at 9:13 pm
The above statement by Fiona Walsh does, unfortunately, not reflect the entire contents of our Reply to the Letter by Walsh et al. but only one fraction of it. In our Reply, we have discussed three possible gap-creating features, namely mound erosion (which is very important in this area near Newman because of the episodic, heavy rainfall events), spatial nest patterns, and hidden flat pavements that may all be associated with Drepanotermes harvester termites. However, the third and main argument in our Reply is not at all addressed by the media release of Walsh et al. That is, we are showing that very large gaps with a size of 5 to 6 m in diameter are formed by the plants themselves – in the complete absence of flat pavements or “ghosts” of hidden underground termitaria. Notably, we have literally cited the well-known criteria mentioned by Walsh et al. that are typical for flat, hidden pavements, but inside of the fairy circles of the area that we address are neither termite pavements “within 5 cm of the surface” nor “very hard pavements, withstanding road grader blades”. Our Reply with its entire contents can be downloaded with additional information on the Australian fairy circles here:
http://www.ufz.de/index.php?en=36656
We highlight in our Reply and in the main PNAS article that any study on the genuine fairy circles that we address needs to account for the physical soil crusts, resulting from mechanical weathering, that are causing the inhibition of plant growth and resulting plant patterns such as fairy circles, stripes (bands) or labyrinths. We do think that only if we adequately address the strong interaction between spinifex vegetation and runoff-erosion processes in this harsh environment, we can fully understand the plant self-organization phenomenon in this area. More research especially with respect to aeolian and water-erosion processes is necessary and we are welcoming any cooperation with Australian environmentalists or environmental researchers. For example, it would be interesting to study the obvious accumulation of numerous stones and pebbles at the soil surface in gaps and spinifex labyrinths of the entire area.
In order to avoid confusion in terminology, it needs to be emphasized that the comparatively small and heterogeneously distributed “desert circles” as shown in the above image of this blog from near Kintore in the Northern Territory, as well as in the PNAS Letter of Walsh et al. (their Fig. 1B) are no mystery at all and cannot be called “fairy circles”. It is clear that such local gaps are caused by termites, a phenomenon that is also well-known from social insects elsewhere in the world. Already in our main PNAS article, as well as in the Reply we are citing Noble et al. 1989 in this respect, an Australian study which described the heterogeneous spatial distribution of “desert circles” created by pavements of the harvester termite.
In summary, biomass-water feedbacks are not only, for example, causing the typical banded Mulga patterns on hill slopes but they have been identified in the field to be essential for forming vegetation biomass gradients and genuine fairy circles, too. Cramer et al. have recently provided new support for the Namibian fairy circle case:
Cramer, M.D., Barger, N.N. & Tschinkel, W.R. (2016) Edaphic properties enable facilitative and competitive interactions resulting in fairy circle formation. Ecography
http://onlinelibrary.wiley.com/doi/10.1111/ecog.02461/full
Plant self-organization does also lead to other vegetation gap patterns in the world such as in arid Niger, see e.g. the work of Barbier et al.:
Barbier, N., Couteron, P., Lejoly, J., Deblauwe, V. & Lejeune, O. (2006) Self-organized vegetation patterning as a fingerprint of climate and human impact on semi-arid ecosystems. Journal of Ecology, 94, 537 – 547.
Barbier, N., Couteron, P., Lefefer, R., Deblauwe, V. & Lejeune, O. (2008) Spatial decoupling of facilitation and competition at the origin of gapped vegetation patterns. Ecology, 89, 1521 – 1531.
January 25, 2017 at 10:32 pm
This work absolutely mirrors work my entomologist colleague, John L Bissett, and I undertook in Southwestern Zimbabwe in southern Africa in the early 1970s. There these otherwise inexplicable bare (often roughly circular) areas in otherwise tuft-perennial grasslands were invariably associated with the subterranean hives of the Harvester Termite Hodotermes mosambicus. The work was interrupted by the bush war and was only partly published (e.g. Macdonald, I.A.W. 1978. Pattern and process in a semi-arid grassveld in Rhodesia. Proc. Grassld Soc. Sthn. Afr. 13: 103-109.). There is also published work on “Fairy Rings” from the semi desert grassland fringes of the Namib Desert in Namibia. Good to see the South-South comparisons!