Modelling topographic influences on vegetation vigour in the Cradle Nature Reserve, Gauteng province, South Africa

Abstract

The study explores topography and vegetation changes in the Cradle Nature Reserve’s landscape, which is characterised by interconnected water infiltration and drainage patterns with geological features such as sinkholes, using indices such as the Enhanced Vegetation Index (EVI), the Topographic Position Index (TPI), the Topographic Ruggedness Index (TRI), and the Topographic Wetness Index (TWI). The high-resolution satellite images, including Sentinal-2A, the Shuttle Radar Topography Mission Digital Elevation Model, and NASSA Power Rainfall, Temperature, and Ground Wetness in the Root Zone-Modern Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), were analysed using advanced statistical models. The software tools Stata/SE v.13.1, QGIS v.3.36, and ArcGIS desktop v. 10.8.2 were utilised for this analysis. The results emphasise the significance of incorporating topography into ecological research and highlight the necessity of focused conservation initiatives to address habitat suitability and erosion risk in challenging landscapes. Specifically, the results show that the Enhanced Vegetation Index (EVI) has a strong negative correlation with the Topographic Position Index (TPI) (R2 = 0.95), indicating that TPI usually decreases as EVI increases. This relationship is influenced by landscape features such as sinkholes and depressions, which impact plant health. Additionally, the strong positive relationship between EVI and percentage slope gradient (R2 = 0.85) offers valuable insights for environmental studies and land management practices. Additionally, TRI shows a negative correlation with EVI (R2 = 0.94), emphasising the impact of terrain ruggedness on vegetation density. TWI analysis strongly correlates with slope gradients (R2 = 0.96), highlighting topography’s role in hydrological dynamics. Despite these insights, we acknowledge limitations such as scale dependency and the inability to capture fine terrain details. Integrating topographic information into ecological assessments and land management strategies is crucial for promoting conservation, sustainable practices, landscape ecology understanding, and biodiversity preservation decision-making.