Legacy Effects of Different Land-Use Histories Interact with Current Grazing Patterns to Determine Grazing Lawn Soil Properties
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Pastoralism and agriculture have affected rangeland ecosystems over the past millennia, including many ecosystems that are currently protected as reserves. However, the legacy of these land-use practices on current ecosystem functioning remains unclear. We studied legacy effects of former human land use on soil physical and chemical properties in a South African savanna. We did this by comparing soil properties in grazing lawns (patches of short grass maintained by the positive feedback between grazing intensity and forage quality) with the surrounding less grazed bunch grasslands within three different human land-use history contexts: (i) Abandoned bomas: permanent stone enclosures where livestock were kept overnight, and dung and urine accumulated for several years or decades. (ii) Old fields: areas where vegetation was cleared, soil tilled, and cultivated, but received little or no fertilization. (iii) Natural grasslands: not cultivated but grazed by livestock before the establishment of the reserve and wildlife thereafter. Former human land use rather than soil texture was the main determinant of grazing lawn location. Moreover, lawn soil properties also varied among land-use histories. In all grazing lawns, soil nutrient concentrations were higher than in adjacent grasslands but abandoned bomas contained three times more phosphorus, and twice as much nitrogen and carbon than old fields and natural grassland lawns. In addition to past land use, soil texture influenced lawn soil nutrients: Concentrations of phosphorus, potassium, calcium, magnesium, total nitrogen, and carbon in lawns were higher on clayey soils than sandy soils, whereas phosphorus, C:N ratio, and pH did not change with soil texture. Our study confirms previous findings on the effect of human land use on savanna heterogeneity, but also highlights how legacy effects may vary among different historic land-use practices.
Keywordssavanna boma nutrient cycling Ithala Game Reserve herbivory resource hotspots
We would like to thank KZN wildlife for giving us the opportunity to conduct our research in Ithala Game reserve. We also thank our colleagues from UKZN particularly Vincent Chaplot (IRD) for advice on soil sample collection and analysis. We are grateful to Jacques Gignoux and Simon Chamaillé-Jammes for their comments on earlier versions of the manuscript. Funding for the project was provided to A.S. (UKZN) by the National Research Foundation (NRF) and to H.F. (LBBE) by the CNRS INEE “Zone Atelier” grant, and the CNRS GDRI Biodiversity Dynamics in Southern Africa. H.V.F. was supported by the Ecole Normale Superieure as an élève fonctionnaire stagiaire. J.P.G.M.C. was supported by a Marie Curie Career Integration Grant (PCIG10-GA-2011-304128) and by the Swedish Thematic research program WILDLIFE & FORESTRY. We thank two anonymous reviewers for their comments which greatly improved a previous version of this manuscript.
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