Abstract
ContextPiospheres describe herbivore utilization gradients around watering points, as commonly found in grass-dominated ecosystems. Spatially explicit, dynamic models are ideal tools to study the ecological and economic problems associated with the resulting land degradation. However, there is a need for appropriate landscape input maps to these models that depict plausible initial vegetation patterns under a range of scenarios. ObjectivesOur goal was to develop a spatially-explicit piosphere landscape generator (PioLaG) for semi-arid savanna rangelands with a focus on realistic vegetation zones and spatial patterns of basic plant functional types around livestock watering points.MethodsWe applied a hybrid modelling approach combining aspects of both process- and pattern-based modelling. Exemplary parameterization of PioLaG was based on literature data and expert interviews in reference to Kalahari savannas. PioLaG outputs were compared with piosphere formations identified on aerial images.ResultsPioLaG allowed to create rangeland landscapes with piospheres that can be positioned within flexible arrangements of grazing units (camps). The livestock utilization gradients showed distinct vegetation patterns around watering points, which varied according to the pre-set initial rangeland condition, grazing regime and management type. The spatial characteristics and zoning of woody and herbaceous vegetation were comparable to real piosphere patterns.ConclusionsPioLaG can provide important input data for spatial rangeland models that simulate site-specific savanna dynamics. The created landscapes can also be used as a direct decision support for land managers in attempts to maintain or restore landscape functionality and key ecosystem services such as forage production.
Highlights
In arid and semi-arid rangelands worldwide, livestock utilization gradients around watering points are commonly used to investigate the ecological effects of grazing on the biotic and abiotic environment (e.g. Adler and Hall 2005; Peper et al 2011; Wesuls et al 2013)
We report on the development of a piosphere landscape generator (PioLaG) based on a hybrid modelling approach that combines aspects of both process- and pattern-based modelling
Though the application ability of PioLaG should not be restricted to this region, its parameterization was based on the ecology of this savanna type and typical forms of local land use and range management
Summary
In arid and semi-arid rangelands worldwide, livestock utilization gradients around watering points are commonly used to investigate the ecological effects of grazing on the biotic and abiotic environment (e.g. Adler and Hall 2005; Peper et al 2011; Wesuls et al 2013). In arid and semi-arid rangelands worldwide, livestock utilization gradients around watering points are commonly used to investigate the ecological effects of grazing on the biotic and abiotic environment Adler and Hall 2005; Peper et al 2011; Wesuls et al 2013) These so-called ‘piospheres’ (Lange 1969) are ideal model systems to understand the interplay between grazing, vegetation, and the abiotic environment and can be used to guide range management with respect to landscape functionality and rangeland productivity (Thrash and Derry 1999). A piosphere can be understood as a spatially concentrated form of land degradation It derives from a radial symmetry of ecological impacts around watering points (or similar animal concentration points like stables or kraals). The livestock density per unit area—and effects of grazing, trampling, and feces accumulation—is highest in direct vicinity to the watering point and decreases with distance from it until effects start to vanish in the rangeland matrix (Andrew 1988), which may appear in a few hundred
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