Assessing the dynamics of land use and land cover change in semi-arid savannah: A focus on woody plant encroachment utilising historical satellite data

The encroachment of woody plants into grassland and the conversion of grasslands to woodlands is a worldwide phenomenon and has been regarded as a major global problem for decades. The rate of woody plant encroachment (WPE) varies across biomes and can be influenced by land use activities and climate conditions. As a result, the current study assessed the spatial distribution of woody plants and land use and land cover (LULC) change within the Letaba River catchment in the Limpopo province of South Africa's subtropical region. Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) satellite data sets were used to map and quantify WPE and other LULC changes in the Letaba River catchment over a 30-year period (1989–2019). Random forest classifier was used to determine of the rate of change of WPE and LULC within the study area. The results indicated that the Letaba River catchment has undergone a significant change with an increase in woody plant species. The woody plant cover had increased from 36,014 ha in the year 1989 to approximately 561,493 ha by 2019. Meanwhile, grassland has declined by 486,322 ha (33.7%) from 1989 to 2019. The overall classification accuracy (OA) ranged between 91.7% and 95.5%. The study findings will provide critical insights and baseline information about the state of WPE in semi-arid environments, as well as provide catchment managers with the information they need to take the necessary actions to manage the rapid increase in woody plants. However, fire and herbivory are important factors that influences the WPE, and this might have also played an important role in the findings. The study suggests that WPE is an ongoing process and management strategies are required to mitigate and maintain the intensity of woody plants.