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Context: Namibia’s fairy circles (FCs) form an extraordinary vegetation pattern along the Namib Desert. Recent evidence from multiple fieldwork activities is increasingly supporting the view that FCs result from biomass-water feedbacks and plant self-organization. Objectives: To shed light on these biomass-water feedbacks, we focused here on a temporal analysis of the spatial FC patterns with regard to vegetation response after rainfall events. Methods: We analyzed the distribution of FCs in 10 drone-mapped study plots of the Namib and related their spatial patterns to the soil infiltrability. Additionally, we mapped three plots repeatedly during the rainfall seasons 2020–2023 to assess how the emerging grasses within FCs changed the FC patterns after rainfall. Results: We found that the most regular, spatially periodic, FCs occurred in areas with deep aeolian sands where rain water infiltrates very quickly and homogenously across the study plot, which enables the most symmetric competitive interactions between the grasses. After ample rainfall following a drought period, between 58 and 34% of all mature FCs revegetated. These 1092 closing FCs were 73 times more than the 15 new FCs that formed during the same time. The closing FCs occurred in areas where there was locally a higher density of FCs, which act as underground water sources for the surrounding grasses. Conclusions: Our study shows that the dynamic vegetation response to rainfall and soil water is the key driver of the FC patterns. Overall, the research underlines that Namibia’s fairy circles are a self-organized emergent vegetation pattern that is driven by biomass-water feedbacks and the competition of grasses for limiting water resources. [ABSTRACT FROM AUTHOR]

Context: Vegetation patterns in hummock grasslands of Australia's arid interior can be very complex. Additionally, the grasslands are interspersed with variable amounts of trees and shrubs. Objectives: To better understand the spatial arrangement of this vegetation structure, and in particular the unvegetated bare-soil gaps, we analyzed the scale-dependent patterns of gaps, trees, and shrubs. Methods: We focused on two size categories of grassland gaps, large gaps ≥ 4 m2 known as fairy circles (FCs) and small gaps 1 to < 4 m2, and on trees and shrubs. We mapped four 200 m × 200 m study plots located east of the town of Newman in Western Australia, using drone-based aerial images and LiDAR. The RGB images were converted into binary images and the gaps and woody plants were automatically segmented. The spatial patterns of the four vegetation components were analyzed, as well as the shape properties of the vegetation gaps. Results: The most striking result was that small gaps appeared consistently at about 5 m distance away from the FCs, which are known as the most water-depleted locations in the grassland. The FCs were also rounder than the small gaps and this symmetry underlines their function as an extra source of water for the surrounding matrix vegetation. Trees and shrubs had spatial patterns that were unrelated to FCs, which likely results from their water uptake in deeper sub-soil layers. Conclusions: The consistent distance of small gaps to FCs is further support that the Australian fairy circles are a self-organized vegetation pattern that results from ecohydrological feedbacks. [ABSTRACT FROM AUTHOR]

Aeolian sand transport is a major process shaping landscapes on Earth and on diverse celestial bodies. Conditions favoring bimodal sand transport, with fine-grain saltation driving coarse-grain reptation, give rise to the evolution of megaripples with a characteristic bimodal sand composition. Here, we derive a unified phase diagram for this special aeolian process and the ensuing nonequilibrium megaripple morphodynamics by means of a conceptually simple quantitative model, grounded in the grain-scale physics. We establish a well-preserved quantitative signature of bimodal aeolian transport in the otherwise highly variable grain size distributions, namely, the log-scale width (Krumbein phi scale) of their coarse-grain peaks. A comprehensive collection of terrestrial and extraterrestrial data, covering a wide range of geographical sources and environmental conditions, supports the accuracy and robustness of this unexpected theoretical finding. It could help to resolve ambiguities in the classification of terrestrial and extraterrestrial sedimentary bedforms. Megaripples are sand landforms found in wind-blown environments. A newly identified characteristic signature of the underlying bimodal sand transport process is found in the grain-size distribution on megaripples and could lend insight into transport conditions on Earth and other planetary bodies. [ABSTRACT FROM AUTHOR]

A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev. The most impacted shrub species is the Noaea mucronata (Forssk.) Asch. and Schweinf. In a four-year study, we found that herbaceous vegetation growth was greater in the dead shrub patches than in the surrounding inter-patch biocrusted spaces, suggesting that the dead shrub patches encompass improved micro-habitats. However, unexpectedly, the soil moisture in the dead shrub patches was consistently lower than that of the inter-patch biocrusted spaces. At the same time, soil quality in the dead shrub patches was higher than that in the inter-patch spaces. Therefore, it seems that the overall better soil conditions in the dead patches overcome the scarcity of soil-water, supporting increased herbaceous productivity. For explaining the discrepancy between herbaceous vegetation and soil-water, we formulated a conceptual framework, which highlights the key factors that regulate soil-water dynamics in this dryland ecosystem. We demonstrate that herbaceous vegetation is facilitated in the dead shrub patches by a legacy effect that takes place long after the shrubs have died. The dead shrub patches encompass a unique form of ecosystem engineering. The study highlights the complex and unpredicted impacts of prolonged droughts on dryland ecosystems. [ABSTRACT FROM AUTHOR]

Geodiversity refers to the variety of geological and physical elements as well as to geomorphological processes of the earth surface. Heterogeneity of the physical environment has an impact on plant diversity. In recent years, the relations between geodiversity and biodiversity has gained attention in conservation biology, especially in the context of climate change. In this study, we assessed the spatial and temporal change in plant's community structure in a semi-arid region, Sayeret Shaked Long Term Ecosystem Research (LTER) station, Israel. Vegetation surveys were conducted on different hillslopes, either with or without rock covers in order to study the spatial trends of hillslope geodiversity. The surveys were conducted for two consecutive years (2016 and 2017), of which the second year was drier and hotter and therefore permitted to investigate the temporal change of plant's community structure. The results of the spatial trends show that (1) geodiversity increases vegetation biodiversity and promotes perennial plants and those of the temporal change show that (2) the positive effect of geodiversity on plants' community structure and species richness is greater in the drier year than that in a wetter year. The main insight is that in these drylands, hillslopes with higher geodiversity appear to buffer the effect of drier years, and supported a more diverse plant community than lower geodiversity hillslopes. [ABSTRACT FROM AUTHOR]

Riverbed terracing has been introduced in ancient times to retain water and soil, to reduce hydrological connectivity and erosion and to increase primary and secondary productivity of agro-ecological systems. These presently abandoned human-made landscapes have become novel ecosystems and a potential source of ecosystem services to humans in drylands. We use a mathematical-modeling approach to study factors that regulate terraced riverbeds and affect community and ecosystem attributes such as productivity, functional diversity and resilience to droughts. We introduce a model that captures the relationships between rainfall pattern, runoff coupling between adjacent terraces, and vegetation growth, taking into account competition for water and light. We found that a large number of weak rainfall events results in lower total biomass and functional diversity across the terraced riverbed compared with a few strong rainfall events. We further analyzed the filtering of species traits from pools of functional groups that make different tradeoffs between investment in above-ground biomass to capture canopy resources and investment in below-ground biomass to capture soil resources. Pools characterized by concave tradeoffs give rise to higher functional diversity, lower biomass production and lower resilience to droughts, as compared with convex pools. New empirical studies are needed to test these model predictions. [ABSTRACT FROM AUTHOR]