Stephan Getzin

Helmholtz-Zentrum für Umweltforschung | UFZ · Department of Ecological Modelling

The fairy circles of Namibia form a remarkable gap pattern in arid grassland along the Namib Desert. The origin of the fairy circles is subject to an ongoing debate. Solving the mystery of the fairy circles (FCs) requires the right timing in fieldwork after rainfall, as the newly appearing grasses complete their life cycle within only a few weeks....

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-...

Aims The fairy circles along the Namib Desert in southern Africa are round grassland gaps that have puzzled scientists for about 50 years. With the discovery of fairy circles in Australia in 2016, the debate on the origin of the circles has been extended to a new continent. Research interest on the topic has since then risen strongly but so has the...

Background: The Euphorbia hypothesis on the origin of fairy circles (FCs) in Namibia dates back to 1979. It proposes that the remains of decaying shrubs would induce an allelopathic interaction with the grasses and thereby cause bare-soil FCs. Here, we investigated this hypothesis based on revisiting marked Euphorbias after four decades, comparing...

1. So‐called fairy circles (FCs) comprise a spatially periodic gap pattern in arid grasslands of Namibia and north‐west Western Australia. This pattern has been explained with scale‐dependent ecohydrological feedbacks and the reaction‐diffusion, or Turing mechanism, used in process‐based models that are rooted in physics and pattern‐formation theor...

Numerical analysis of spatial pattern is widely used in ecology to describe the characteristics of floral and faunal distributions. These methods allow attribution of pattern to causal mechanisms by uncovering the specific signatures of patterns and causal agents. For example, grassland‐gap patterns called fairy circles (FCs) in Namibia and Austral...

Under homogeneous habitat conditions, fairy circles are extremely ordered grassland gaps that are densely packed and that function as an extra source of water for the surrounding matrix vegetation. While the origin of fairy circles is still disputed, most of the research has so far focused on such typical habitat conditions where the fairy circles...

Fairy circles (FCs) are extremely ordered round patches of bare soil within arid grasslands of southwestern Africa and northwestern Australia. Their origin is disputed because biotic factors such as insects or abiotic factors such as edaphic and eco‐hydrological feedback mechanisms have been suggested to be causal. In this research, we used a multi...

Seed dispersal by frugivores, particularly primates, plays an important role in structuring and maintaining tree diversity in tropical forests. However, little is known about the effect of frugivores on the diversity of saplings and large trees. We used detailed census data from the fully mapped 30-ha Mo Singto forest dynamics plot in Thailand toge...

Context Field inventory plots which usually have small sizes of around 0.25–1 ha can only represent a sample of the much larger surrounding forest landscape. Based on airborne laser scanning (LiDAR) it has been shown for tropical forests that the bias in the selection of small field plots may hamper the extrapolation of structural forest attributes...

Significance Pattern-formation theory predicts that vegetation gap patterns, such as the fairy circles of Namibia, emerge through the action of pattern-forming biomass–water feedbacks and that such patterns should be found elsewhere in water-limited systems around the world. We report here the exciting discovery of fairy-circle patterns in the remo...

Over the last two decades spatial point pattern analysis (SPPA) has become increasingly popular in ecological research. To direct future work in this area we review studies using SPPA techniques in ecology and related disciplines. We first summarize the key elements of SPPA in ecology (i.e., data types, summary statistics and their estimation, null...

Interactions among neighboring individuals influence plant performance and should create spatial patterns in local community structure. In order to assess the role of large trees in generating spatial patterns in local species richness, we used the individual species-area relationship (ISAR) to evaluate the species richness of trees of different si...

The spatial placement of recruits around adult conspecifics represents the accumulated outcome of several pattern-forming processes and mechanisms such as primary and secondary seed dispersal, habitat associations or Janzen-Connell effects. Studying the adult-recruit relationship should therefore allow the derivation of specific hypotheses on the p...

Gap distributions in forests reflect the spatial impact of man-made tree harvesting or naturally-induced patterns of tree death being caused by windthrow, inter-tree competition, disease or senescence. Gap sizes can vary from large (>100 m2) to small (<10 m2), and they may have contrasting spatial patterns, such as being aggregated or regularly dis...

Streblus macrophyllus is a shade-tolerant and subcanopy tree species common to tropical evergreen forests in northern Vietnam. However, its ecology is poorly known. We used spatial point pattern analysis to describe the spatial arrangement of tree individuals within a forest community dominated by S. macrophyllus. All individual trees with diameter...

Ecological interactions of species and thus their spatial patterns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locations of tree individuals from two 1-ha tropicalforest plots in Vietnam. We analyzed the effect of environmental heterogeneity on tree d...

The mysterious ‘fairy circles’ are vegetation‐free discs that cover vast areas along the pro‐Namib Desert. Despite 30 yr of research their origin remains unknown. Here we adopt a novel approach that focuses on analysis of the spatial patterns of fairy circles obtained from representative 25‐ha aerial images of north‐west Namibia. We use spatial poi...

Niche and neutral theories emphasize different processes that contribute to the maintenance of species diversity and should leave different spatial structures in species assemblages. In this study we used variation partitioning in combination with distance-based Moran's eigenvector maps and habitat variables to determine the relative importance of...

The Janzen-Connell hypothesis is among the most important theories put forward to explain species coexistence in species-rich communities. However, the relative importance of Janzen-Connell effects with respect to other prominent mechanisms of community assembly, such as dispersal limitation, self-thinning due to competition, or habitat association...

1. One of the primary goals in community ecology is to determine the relative importance of processes and mechanisms that control biodiversity. Here, we examined habitat-driven species assemblages and species distribution patterns as well as their temporal variations for three life stages of two censuses of a 25-ha mixed dipterocarp forest at Sinha...

Walter (Jahrb Wiss Bot 87:750–860, 1939) proposed a two-layer hypothesis, an equilibrium explanation for coexistence of savanna trees and grasses. This hypothesis relies on vertical niche partitioning and assumed that grasses are more water-use efficient than trees and use subsurface water while trees also have access to deeper water sources. Thus,...

Studying the spatial pattern and interspecific associations of plant species may provide valuable insights into processes and mechanisms that maintain species coexistence. Point pattern analysis was used to analyze the spatial distribution patterns of twenty dominant tree species, their interspecific spatial associations and changes across life sta...

[This corrects the article DOI: 10.1371/journal.pone.0046074.].

Habitat of the 20-ha permanent plot of tropical seasonal rain forest in China. Valley: slope<27.1°, elevation<764.87 m; Low-slope: slope>27.1°, elevation<764.87 m; High-slope: slope≥27.1°, elevation≥764.87 m, convexity>0; High-gully: slope≥27.1°, elevation≥764.87 m, convexity<0; High-plateau: slope<27.1°, elevation≥764.87 m, convexity>0; Gap: with...

Spatial associations of twenty dominant species across life stages in 20-ha permanent plot of tropical seasonal rain forest in China. The bivariate statistic of the pair-correlation function was used to analyze the spatial associations among five canopy species under the heterogeneous Poison null model. “p” stands for positive association, “r” stan...

Distribution maps of the twenty dominant species across life stages in the 20-ha plot of tropical seasonal rainforest. See Table 1 for species codes. Green cross: saplings, blue open circle: poles, red solid circle: adults. (TIF)

Univariate patterns of the twenty dominant species across life stages in the 20-ha plot of tropical seasonal rainforest. Shown are the univariate g11 pair-correlation functions of the data in dependence on scale r (solid squares), and the expected g11(r) function under the heterogeneous Poisson null model (open squares) and the Monte Carlo simulati...

The assertion that the spatial location of different species is independent of each other is fundamental in major ecological theories such as neutral theory that describes a stochastic geometry of biodiversity. However, this assertion has rarely been tested. Here we use techniques of spatial point pattern analysis to conduct a comprehensive test of...

1. Structural diversity and niche differences within habitats are important for stabilizing species coexistence. However, land-use change leading to environmental homogenization is a major cause for the dramatic decline of biodiversity under global change. The difficulty in assessing large-scale biodiversity losses urgently requires new technologic...

Does competition prevail in large size classes of trees in tropical forests? This question is fundamental to our understanding of the demography and dynamics occurring in rain forests. We investigated this question based on an undisturbed late-secondary forest on a 1-ha plot in central Cameroon. Trees were stem-mapped and classified into three size...

Summary 1. The spatial pattern of tree species retains signatures of factors and processes such as dispersal, available resource patches for establishment, competition and demographics. Comparison of the spatial pattern of different size classes can thus help to reveal the importance and characteristics of the underlying processes. However, tree dy...

The detection and quantification of competition at the stand level is important in forest management because competition reduces growth and increases the risk of mortality. This is of interest for timber production where efficient tools of forest inventory are increasingly demanded. Especially modern planning of thinning based on aerial or satellit...

a b s t r a c t Nearest tree neighbour distances and the tree spatial formation on a large scale over time and space replicates were examined. The study was conducted in a natural savanna eco-system in the Southern Kalahari, South Africa. Nearest tree neighbour and point pattern analysis methods were used to investigate changes in the spatial patte...

Asymmetric tree growth is an adaptation to maximise photosynthesis by growing in response to gaps and neighbours, topographical site conditions or incoming solar radiation. Whereas spatial statistics have been widely used to study the distribution of trunk locations, less research has been undertaken to analyse the distribution of crown centres and...

While the successional dynamics and large-scale structure of Douglas-fir forest in the Pacific Northwest region is well studied, the fine-scale spatial characteristics at the stand level are still poorly understood. Here we investigated the fine-scale spatial structure of forest on Vancouver Island, in order to understand how the three dominant spe...

The Degradation Gradient Method (DGM) is a sophisticated technique for the assessment of range condition. It applies multivariate analyses of herbaceous species data to detect subtle degrees of overgrazing. The suitability of this multivariate method was tested in the central Highland Savanna of Namibia by comparing its results against a univariate...

AbstractEmbedded in species-poor grasslands, fairy circles are circular or sub-circular patches devoid of any vegetation. Characteristically, the circumference of each circle shows a band of more densely packed taller tussocks within a shorter, more sparse grassland matrix. The average diameter of the circles is between 58 m. Restricted to sites sh...