Vulnerability and Resilience of Soils under Different Rangeland Use
Final Report Abstract
South Africa’s rural areas are currently undergoing rapid changes due to land tenure reform and changing patterns of land use. The project focused on the mutual interdependencies of soil and vegetation dynamics and social change in two selected areas of South Africa: (1.) the grassland biome in the Orange Free State, and (2.) the savannah biome in the Northern Cape Province. Changes in the grass communities and invasions of woody plants are severely threatening the economic viability of pastoralism in both biomes. However, the causes of and the processes involved in these changes and human interactions with them remained poorly understood. Our aim was, therefore to elucidate how and to which extent soil properties respond to different types and intensities of rangeland use in the grassland and savannah biome in semiarid South Africa. In particular we aimed at understanding: (1) Which soil properties and mechanisms reflect most sensitively the impact of different kinds of rangeland use? How is the perception of soil by the farmers? (2) Are microbial communities in soils influenced by different rangeland management systems? (3) Which present or past vegetation structures control the spatial patterns of soil properties in the different rangeland systems of the savannah biome? (4) What is the age and pattern of bare patches in the grassland biome, and how these are affected by management? To answer these questions, we identified sites with different parent material and different tenure systems (common property, municipal commonages, commercial farms, and nature reserve areas). At each site we sampled gradients away from the water points as well as open fields to cover changes in species composition (grassland biome) and bush encroachment (savannah biome) as induced by different land use histories and grazing intensities. We then analyzed spatial distribution of nutrients, aggregate stability, and biomarkers in both biomes. We found that the grazing system (continuous vs. rotational) significantly influenced soil properties. In the grassland biome, soils degrade by aggregate disruption and associated organic matter losses, whereas those in the savannah biome improve with increasing grazing pressure because of nutrient reallocations from the invasion of brush. Yet, the effects were patchy, i.e., the spatial-temporal variability of soil properties seems to control their vulnerability and resilience to the management system. In the grassland biome, formation of bare patches accompanies rangeland degradation, which is of concern to farmers. Yet only few people really depend on rangeland income, so that the ecological system, at least at Thaba Nchu, is increasingly decoupled form the social one. In the Kuruman savannah biome instead, rangeland degradation is a slow process, with ages of invaded bush frequently exceeding 30 years; hence, many of these are not been perceived by farmers, thus preventing incentives and options to react.
Publications
- (2013) Rangeland management impacts on the properties of clayey soils along grazing gradients in the semi-arid grassland biome of South Africa. J. Arid Environ. 97, 220-229
Kotze, E., Sandhage-Hofmann, A., Meinel, J.-A., du Preez, C.C., Amelung, W.
(See online at https://doi.org/10.1016/j.jaridenv.2013.07.004) - (2014) Stability and Transformation in a South African Landscape: Rural Livelihoods, Governmental Interventions and Agro-economic Change in Thaba Nchu. Journal of Southern African Studies 40(1): 41-57
Naumann, C.
(See online at https://doi.org/10.1080/03057070.2014.877653) - (2015) Rangeland management effects on soil properties in the savanna biome, South Africa: A case study along grazing gradients incommunal and commercial farms. J. Arid Environ 120, 40-125
Sandhage-Hofmann, A. Kotze, E. van Delden, L., Dominiak,M. Fouche, H.J., van der Westhuizen, H.C., Oomen, R.J., du Preez, CC. Amelung, W.
(See online at https://doi.org/10.1016/j.jaridenv.2015.04.004) - (2016) Assessing the resilience of a real-world social-ecological system: lessons from a multidisciplinary evaluation of a South African pastoral system
Linstädter, A., Kuhn, A. , Naumann, C., Rasch, S., Sandhage-Hofmann, A., Amelung, W., Jordaan, J., Du Preez, C.C., Bollig, M.
(See online at https://doi.org/10.5751/ES-08737-210335) - (2016) Rangeland Management – A review. Reference Module in Earth Systems and Environment
Sandhage-Hofmann, A.
(See online at https://doi.org/10.1016/B978-0-12-409548-9.10455-5) - (2017) Growth rings in bush species of the South African savannah. African Journal of Ecology. 1-5
Zacharias, M., Weijers, S., Löffler, J.
(See online at https://doi.org/10.1111/aje.12440) - (2017).Soil microbial communities in different rangeland management systems of a sandy savanna and clayey grassland ecosystem, South Africa. Nutrient Cycling in Agroecosystems, Nutr Cycl Agroecosyst.
Kotze, E., Sandhage-Hofmann, A., Amelung, W., du Preez, CC.
(See online at https://doi.org/10.1007/s10705-017-9832-3)
