Investigating the spatial mechanisms of self-organized vegetation gaps in arid Australia

• Applicant: Dr. Stephan Getzin
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 323093723

Distinct vegetation patterns that change from gaps, stripes, to spots with decreasing plant-available moisture are a conspicuous phenomenon in arid environments but their causes are so-far little understood. Based on pattern-formation theory, physicists and mathematicians have successfully modelled these patterns under the a priori assumption that the different morphologies are induced by vegetation self-organization resulting from positive feedbacks between local vegetation growth and water transport toward the growth location. However, the proposed spatial mechanisms of the biomass-water feedbacks are until now only poorly documented in the field and a posteriori evaluated within a spatially explicit framework. Furthermore, in contrast to more common patterns such as stripes of Tiger bush or vegetation spots, evidence for gap patterns in arid environments is very rare.In a pioneering research project we therefore aim to investigate the ecological foundations of vegetation self-organization based on a new discovery of a largely unexplored grassland gap pattern in the interior of Western Australia. This ecosystem is special in that it shows in a single region with the dominant spinifex grass Triodia basedowii also the spectrum of vegetation states such as spots, labyrinths, gaps and even rings that are normally seen in different regions along a rainfall gradient. Therefore, we consider this outstanding discovery as a unique benchmark ecosystem to study the mechanisms of self-organization under similar environmental conditions and why the different patterns co-exist unusually all in one region. Since recurrent fire disturbance plays a crucial role in the landscape, this system allows also an in-depth investigation of the spatio-temporal interaction between abiotic drivers and biotic feedbacks and its effects on pattern formation. By using a high-tech drone with a laser scanner, photo, multispectral, and thermal camera, we will map the distribution of individual plants and vegetation gaps at increasing time after past fire. These spatially explicit, high-resolution data will resolve dynamic changes of gradients of biomass and vitality at the individual plant level and thus allow detailed insights into the proposed biomass-water feedbacks. The drone-based data will be also complemented with ground-based measurements of soil moisture and temperature. Additionally, three manipulative field experiments will be conducted to search for empirical evidence for the biomass-water feedbacks that have so-far only been successfully modeled (see Getzin et al. 2016, PNAS). Scale-dependent feedbacks and resulting periodic vegetation patterns of a specific periodicity (e.g. hexagonal) are at the heart of pattern-formation theory. Thus, all the data will be analyzed with spatial statistics and specific null models to formally test if the scales of plant interaction are indeed matching the spatial mechanisms predicted by that theory.

• DFG Programme: Research Grants