Abstract: Hypotheses about the origin of vegetation pattern formation in semi-arid areas around the world almost all include a common feature of semi-arid areas: the presence of a positive feedback between plant density and water infiltration We investigate whether this positive feedback and the spatial redistribution of runoff water are sufficient to explain vegetation pattern formation For this purpose, we analyze a spatially explicit model con- sisting of partial differential equations using a method for demonstrating pattern formation (Turing analysis) Our analysis reveals that pattern formation can occur in semi-arid areas given only the positive feedback between plant density and local water infiltration coupled with the spatial redistribution of runoff water Thus, slope and underlying heterogeneity are not essential conditions Other factors in the model, such as herbivory, plant dispersal, rainfall, and drought tolerance of plants, appear to determine under what conditions pattern formation is likely but are not the primary factors that generate the patterns The model is in agreement with field observations and indicates the conditions for which vegetation pattern formation can be expected in arid and semi-arid grazing systems

Abstract: Banded vegetation patterns and related structures * Theories on the origins, maintenance, dynamics and functioning of banded landscapes * Specific methods of study * Runoff and Erosion Processes * Soil Water balance * Soil Biota in Banded Landscapes * Vegetation dynamics: recruitment and regeneration in two-phase mosaics * Multiscale Modelling of Vegetation Bands * Landscape Models for Banded Vegetation Genesis * Productivity of patterned vegetation * Towards Improved Management of Arid and Semi-Arid Banded Landscapes * Banded landscapes: Ecological Developments and Management Consequences

Abstract: Patterned landscapes are characterized by the banding of perennial, usually dense vegetation on the contour, separated from more-or-less unvegetated soil. The vegetated section acts as a sink area, sequestering soil sediments, water, and nutrients shed from the bare source area immediately above it in the landscape. Water avail-ability is the driving force in patterned landscapes, controlling the structure and the dynamics of the vegetation. Runoff generated on the source zones is trapped on the upslope areas of the sink zones where infiltration proceeds. At the same time, erosion of the lower surface of the vegetated zone is occurring so that the vegetated band gradually moves upslope (Ambouta 1984; Thiery, d’Herbes, and Valentin 1995). Given the importance of overland flow in the formation and maintenance of patterned vegetation, it follows that factors that influence the amounts and distribution of runoff and infiltration will ultimately affect the patterning phenomenon itself.

Abstract: In the course of this book, the patterning of banded vegetation has been described at various scales (chapters 1 and 4), a theory of its genesis has been proposed (chapters 2 and 3), and many of the internal processes of patterns have been summarized (chapters 5 and 11).

Abstract: Summary 1 Vegetation cover regularly punctuated by spots of bare soil is a frequent feature of certain semi-arid African landscapes, which are also characterized by banded vegetation patterns (i.e. tiger bush). 2 The propagation-inhibition (PI) model suggests that a periodic pattern characterized by a dominant wavelength can theoretically establish itself through a Turing-like spatial instability depending only on a trade-off between facilitative and competitive interactions among plants. Under strictly isotropic conditions, spotted and banded patterns are distinct outcomes of a unique process, whereas anisotropy leads to a banded structure. The model predicts that spotted patterns will have a lower dominant wavelength than bands. 3 We test some outcomes of the PI model against vegetation patterns observable in aerial photographs from West Africa. Two sites with rainfall of c. 500–600 mm year−1 were studied: a 525-ha plain in north-west Burkina Faso and a 300-ha plateau in southern Niger. Digitized photographs were subjected to spectral analysis by Fourier transform in order to quantify vegetation patterns in terms of dominant wavelengths and orientations. 4 Spotted vegetation proved highly periodic. The characteristic range of dominant wavelengths (30–50 m) was similar at two sites more than 500 km apart. The PI model suggests that spots may occur as a hexagonal lattice but there is little evidence of such patterning in the field. A dominant wavelength was far quicker to establish in simulations (c. 102–103 years for annual grasses) than a hexagonal symmetry (c. 105 years), and observed patterns are therefore likely to be far from the asymptotic structure. 5 Elongated and smudged spots that locally became flexuous bands have been observed in southern Niger. This pattern that had a dominant wavelength of 50 m but lacked any dominant orientation can be interpreted as a transition from spots to bands under fairly isotropic conditions. 6 The PI model provides a framework for further investigation of patterns in semi-arid vegetation and may be of a broader ecological application.