Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Determining the effect of soil on bush encroachment between 1993 and 2018 in the North West Province

Auteur : Cloete, Willie Herman

Université de soutenance : North-West University

Grade : MSc (Environmental Sciences) 2022

Résumé partiel
Bush encroachment (BE) is a serious form of land degradation and South Africa alone has lost an estimated 8 million hectares (ha) of grazing or cultivation land due to BE. This consequently leads to decreased food security. To prevent BE, one needs to understand the drivers and mechanisms that control the process and to advise when and where certain management actions should be implemented. Unfortunately, the proposed drivers for BE in African savannas are still widely debated given that the causes for this process is still poorly understood. The focus of this study was to understand the effect of soil type and certain soil properties on BE in the North West Province (NWP) between 1993 and 2018. For this study, the main driving factors of BE extent and spread were identified in the study area for the specified period by taking a GIS approach on provincial (NWP) and regional scales (four significant areas). Maps indicating the percentage (%) of woody cover for the years 1993, 1998 and 2018 were sourced from Symeonakis et al. (2020). The layers indicating the % woody cover in the NWP were used for calculating the spread of bush and bush spread maps were created for time frames, 1993-1998, 1998-2018 and 1993-2018. Potential driving factors of BE were sourced from various sources and used to analyse the bush spread and determine the driving factor/s of the specific bush spread from 1993 to 2018 on a provincial scale and regional scale. On a provincial scale, mean annual precipitation (MAP) was the main driving factor of BE, while in land-managed areas, land-use and MAP together with soil, were important driving factors of bush encroachment from 1993 to 2018. Therefore, soil can be regarded as a minor driving factor of BE in the NWP from 1993 to 2018. Vegetation surveys were also carried out at the study sites, characterising different soil types, soil properties and degrees of BE. The belt-transect method was used for the vegetation survey to determine the composition, density, and structure (height classes) of the woody component (tree- and shrub species).

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