Abstract
Vegetation in dryland ecosystems often forms remarkable spatial patterns. These range from regular bands of vegetation alternating with bare ground, to vegetated spots and labyrinths, to regular gaps of bare ground within an otherwise continuous expanse of vegetation. It has been suggested that spotted vegetation patterns could indicate that collapse into a bare ground state is imminent, and the morphology of spatial vegetation patterns, therefore, represents a potentially valuable source of information on the proximity of regime shifts in dryland ecosystems. In this paper, we have developed quantitative methods to characterize the morphology of spatial patterns in dryland vegetation. Our approach is based on algorithmic techniques that have been used to classify pollen grains on the basis of textural patterning, and involves constructing feature vectors to quantify the shapes formed by vegetation patterns. We have analysed images of patterned vegetation produced by a computational model and a small set of satellite images from South Kordofan (South Sudan), which illustrates that our methods are applicable to both simulated and real-world data. Our approach provides a means of quantifying patterns that are frequently described using qualitative terminology, and could be used to classify vegetation patterns in large-scale satellite surveys of dryland ecosystems.
Highlights
Vegetation in dryland ecosystems of Africa, North America, Australia and Asia often forms remarkable spatial patterns
Shapes are distinguished by their complements, and in the context of the binary images in our dataset, the foreground shapes formed of white pixels are reflected in the background shapes formed of black pixels and vice versa
We suspect that the clear characterization of modelled vegetation patterns using foreground pixels might be related to the fact that these simulated vegetation patches are displayed as uniform green–yellow pixels with distinct and regular borders
Summary
Vegetation in dryland ecosystems of Africa, North America, Australia and Asia often forms remarkable spatial patterns. These range from regular bands of vegetation alternating with bare ground, to vegetated spots and labyrinths, to regular gaps of bare ground within an otherwise continuous expanse of vegetation. At relatively high rainfall levels, the entire land surface is covered with vegetation, and as the rainfall progressively decreases vegetation patterns change from gaps (near continuous vegetation cover with small openings) to labyrinths (reticulate networks of vegetation) to spots (small patches of vegetation), and to bare ground (figure 1b; [10,12]).
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