Land cover change and its effect on landscape function in the Koue Bokkeveld

[摘要] ENGLISH ABSTRACT: Natural vegetation and wetlands in regions of the Western Cape are being replaced by agricultural development. Previous studies on one such region - the Koue Bokkeveld, a high mountainous region at the source of three major drainage basins, demarcated for study purposes to cover nearly 2500 km2, have failed to provide a comprehensive overview of such change and its landscape outcomes. This research aimed to detect, capture, record and classify the spatial nature, extent and change dynamics of various landscape elements and functions due to change in the land cover of this region. It assembled a comprehensive spatial database by digitising existing maps, aerial photograph mosaics and satellite imagery. Land cover maps were created for three historical and land cover change analyses were performed for the interim periods. Morphological landscape images were derived from a DEM and used to explain and interpret the location of land cover types and trends in change patterns. The effects on three landscape functions were determined, namely modelled run-off production, biodiversity deduced from landscape pattern structure and SANBI ratings, and carbon storage potential based on published figures.The research found that the regional landscape has undergone substantive land cover change , since the reference state. Increased intensity and productivity of agriculture and its related infrastructure increased its coverage to nearly 45 000 ha or 20 % of the total area. Perennial agriculture (nearly 10 000 ha of orchards and plantations) and annual (intensive vegetable growing and diminishing cereal crops) agriculture, accompanied by improved enabling infrastructure, such as irrigation technology (large storage dams, pipelines, micro delivery modes), transportation, roads, product cooling and packing plants, have extensively replaced natural vegetation. Located in valley bottoms and along toe-slope locations, where they compete for space directly with expanding and constantly intensifying agricultural activities, wetlands, shale fynbos and renosterveld face complete replacement. Land use and land cover changes have profoundly affected landscape functioning. Modelled rainfall run-off has increased (2% overall) in most subregions, opening possibilities for sedimentation and erosion. A high degree of fragmentation of the vulnerable and affected vegetation types threatens biodiversity. Increased carbon storage in perennial agriculture offers a benefit of change, as opposed to the negative outcomes on biodiversity of change in the Koue Bokkeveld.The research recommends improved institutional provision of the data required for system and regional modelling of processes like run-off in developing communities and for meeting the requirements of more sophisticated and accurate landscape models. Improved availability and appropriateness of GIT software solutions to conduct regional research and the use of more economical open software for GIS applications are to be encouraged. Ongoing and improved management and control are advocated for the expanding and intensified agriculture in a sensitive fynbos setting and for the maintenance of healthy landscape functioning. Concerning the discipline of geography, the exploitation of landscape functioning as a transdisciplinary focus inherent to a new regional geography is encouraged to arrest disciplinary drift. Specifically, future research should intensify the examination of the linkages between land use, land cover, change and ecological landscape functioning.

[发布机构] Stellenbosch University