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Environmental stress and landscape recovery in a semi-arid area, the Karoo, South Africa

Boardman, J., Foster, I. D. L., Rowntree, K. M., Mighall, T. M. and Gates, J. B. (2010) Environmental stress and landscape recovery in a semi-arid area, the Karoo, South Africa. Scottish Geographical Journal. 126(2), pp. 64-75. 1470-2541.

Item Type: Article
Abstract: Semi-arid landscapes are vulnerable to cultivation, overgrazing and climate variability, although it is difficult to identify the relative significance of these three factors. In the South African Karoo, the ‘desertification debate’ seeks to explain a change to more shrubby vegetation in heavily grazed areas. We examine these issues in catchments where farm reservoirs provide sediment stores with 137Cs, 210Pb, geochemical and mineral magnetic signatures. Rainfall data and stocking numbers are reported and current erosion rates are estimated. Sediment accumulation in the reservoirs increases between 1935 and 1940, probably due to rises in the frequency of rainfall events of 425mm day. Significant increases in sedimentation rates (68) occur during rain-fed wheat cultivation. In an uncultivated catchment, sediment yields remain relatively high and reflect increases in erosion from hillslopes, colluvial storage, and cultivated land sources. Gully systems have acted as transport routes rather than sediment sources over the last ~70 years. Badland erosion rates average ca. 50t ha-1 yr-1. At Ganora, their development in the 1920s strongly influences peak sedimentation between 1970 and 1980. Any delay between badland initiation and increased sediment yield appears to be a function of landscape connectivity. Recovery following disturbance is occurring slowly and is likely to take ~100 years. De-stocking and better management systems are reducing erosion rates but may be offset by increases in rainfall intensity
Uncontrolled Keywords: Land degradation; semi-arid environment; soil erosion; overgrazing; Karoo
Subjects: Q Science > QE Geology > QE500 Dynamic and structural geology > QE570 Weathering. Erosion
S Agriculture > S Agriculture (General) > S589.75 Agriculture and the environment
G Geography. Anthropology. Recreation > GB Physical geography > GB400 Geomorphology. Landforms. Terrain > GB440.S6 Geomorphology of South Africa
S Agriculture > S Agriculture (General) > S900 Conservation of natural resources, including land conservation
Q Science > QE Geology > QE500 Dynamic and structural geology > QE571 Sedimentation and deposition
Creators: Boardman, John, Foster, Ian D L, Rowntree, Kate M, Mighall, T M and Gates, John B
Publisher: Routledge
Faculties, Divisions and Institutes: Faculties > Faculty of Arts, Science & Technology > Environmental Science
Date: June 2010
Date Type: Publication
Page Range: pp. 64-75
Journal or Publication Title: Scottish Geographical Journal
Volume: 126
Number: 2
Language: English
ISSN: 1470-2541
Status: Published / Disseminated
Refereed: Yes

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