Origin and dynamics of Namibian fairy circles assessed in-situ and by high-resolution spatio-temporal analysis

• Applicant: Dr. Stephan Getzin
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433057155

Fairy circles have been puzzling scientists for decades. What is the process that causes hundreds of thousands of circular vegetation gaps in arid grasslands with such a strongly ordered pattern? There are two main theories to explain these vegetation gaps of about 4-6 m in diameter. The termite theory argues that insects cause the gaps in the grassland. The theory of plant self-organization states that the grasses compete for the sparse soil water, so that biomass-water feedbacks cause the periodically ordered patterns.For Australia, it has recently been shown that there is no causal relationship between termites and the fairy circle patterns. For Namibia, where termites correlate more strongly with fairy circles, the causal relationship has never been investigated systematically for large areas and various regions. This includes in particular the temporal development and spatial patterns of newly forming fairy circles.In this research project, the cause of the formation of fairy circles in Namibia will be systematically investigated for the first time, with a focus on high-resolution spatio-temporal analysis. With the help of drones, the newly formed circles will be mapped every two weeks for two months during the vegetation period. This is necessary because it is so far unknown how fast new fairy circles form and which patterns they have in relation to established mature circles. Parallel to the drone mappings, in-situ investigations in the field will clarify the extent to which termites or abiotic factors such as water scarcity are responsible for the new gaps. The high temporal resolution makes it possible for the firsttime to clarify whether the new circles initially develop without insect activity and are colonized by termites only weeks later. These studies will be carried out over three years for 75-ha areas in several regions of Namibia, covering different soil conditions and rainfall gradients. Using multispectral and photo-drone images, plant vitality is mapped area-wide around the fairy circles and linked with in-situ soil-moisture measurements, allowing deeper insights into the spatial mechanisms of gap formation. Data loggers will also be installed to record the soil moisture in and around the fairy circles over several years. Furthermore, field experiments will be carried out to investigate the influence of the plant architecture of certain grass species on the formation of fairy circles.Comprehensive spatial-statistical analyses will generate a deeper understanding of the dynamic formation of new fairy circles, but also of the revegetation of old fairy circles. This will advance the basic knowledge on pattern formation in arid grasslands and also enable a more precise modelling of vegetation patterns.

• DFG Programme: Research Grants