Exploring the impacts of active faulting & tectonics on the vegetation cover of the dynamic Serengeti-Mara and Ngorongoro ecosystems of East Africa through spectral index analysis

The study of how topographic and geological complexities drive vegetation dynamics over extended timescales, provides critical insights into the interactions between landscapes and ecosystems. Our study area encompasses the Greater Serengeti-Mara Ecosystem (GSME) in the Kenya-Tanzania transboundary region, renowned for its ecological richness and dynamic environments, most famously as the setting for the world’s largest terrestrial mammal migration. We focus on two case study regions: the Mara River Basin (MRB) and the Ngorongoro Conservation Area (NCA) to investigate localized interactions between geological, topographic, and ecological processes. The ecosystems are supported by a healthy and diverse vegetation cover, impacted by natural as well as anthropogenic factors. MRB is bounded in the north by active normal faulting dominated by Utimbara and Isuria faults whereas NCA is centred on Ngorongoro Crater, a large volcanic caldera. The tectonics of NCA is well-studied but subrecent faulting of Utimbara and Isuria was previously unrecognised and the impacts of these faults on uplift, subsidence and tilting of MRB has been revealed only recently. Previous studies have explored the relationship between precipitation and vegetation dynamics in the region. Limited research has focused on soil properties, primarily examining the effects of volcanic ash on the southeastern sector of GSME. However, the role of tectonics in influencing vegetation and, by extension, the broader ecosystem remains underexplored. We used remote sensing data (Landsat 5, 7, 8 and Sentinel 2) to create a time series analysis from the years 1984 until 2024 to examine the changes in the vegetation cover in the study area. Landsat 7 & 8 and Sentinel 2 data were processed in Google Earth Engine whereas those from Landsat 5 & 7 using Erdas Imagine. The normalised differential vegetation index (NDVI) shows a clear difference in vegetation cover during wet and dry seasons throughout the four decades for both the regions. MRB, which is covered by Quaternary sediments, has a higher vegetation cover throughout the year. NCA is affected by intermittent ash eruptions from Oldoinyo Lengai and has a vegetation cover, which varies at differing altitudes within the region and also shows a considerable seasonal variation at lower altitudes. Additionally, there is a significant difference in precipitation between MRB and NCA. In such a scenario, the vegetation cover in both the regions is likely to be a function of the interaction between the inherent soil properties and precipitation. Interestingly, stable vegetation also persists along active faults. Fault escarpments and fault-bounded wetlands provide seasonally stable vegetation cover, potentially due to localized influences on hydrology and soil properties and may serve as refugia during dry seasons. Our preliminary results highlight the need to integrate geo-tectonic analysis into broader ecosystem studies to better understand their role in sustaining biodiversity and ecosystem resilience.