Browsing by Author "Gqaleni, Nosipho Onwabile"
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- ItemSeasonal patterns of evapotranspiration, soil moisture, rainfall, and normalized difference vegetation index in a Nama-Karoo ecosystem(Stellenbosch : Stellenbosch University, 2023-03) Gqaleni, Nosipho Onwabile; Midgley, Guy; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH SUMMARY: This study mainly focused on the South African semi-arid region, the Eastern Karoo, which is located on an ecotone between the Nama Karoo and the Grassland Biomes. The Eastern Karoo is classified as a summer rainfall area, and is known for its highly variable rainfall patterns, which vary in time, space, amount and duration. Seasonal changes in rainfall patterns can affect the hydrological cycle, environmental processes, vegetation, and other biological processes of this region. Dryland ecosystems such as in the Eastern Karoo seem to be one of the most responsive ecosystems to climate change and rising atmospheric CO2, for example, leading to globally widespread desert “greening”. Despite these important changes underway globally and locally, and the value of semi-arid systems in southern Africa, much remains to be learned about their functioning and resilience in response to biophysical drivers. The main aim of this study was to determine if the soil moisture regime, and the related vegetation evapotranspiration and production response to rainfall and other climatic drivers in the Eastern Karoo are predictably linked, and if the ecosystem shows predominantly “pulsed” (eventdriven) or seasonal functioning. The inter-biome ecotonal location was specifically selected to enhance the likelihood of gathering data representing a range of climatic conditions over a succession of years. Results suggest that while soil moisture in this system is somewhat more strongly event-driven rather than seasonally driven, particularly for shallow soil depths, system evapotranspiration appears to be under strong plant physiological control, especially via a reliance of evapotranspiration on deeper soil moisture. These findings do not support the notion that the Nama-Karoo is strongly event-driven with respect to vegetation physiological activity. They also do not support the inference that ongoing climate change will necessarily increase evapotranspiration and cause system aridification. Results for vegetation productivity showed that average normalized difference vegetation index (NDVI) is driven by evapotranspiration and air temperature, not soil moisture, while short term shifts in NDVI (DNDVI) are driven by rainfall and soil moisture conditions. Finally, in-field daily average NDVI measurements on a dominant grass species strongly indicated that shallow soil moisture is a significant driver of the C4 grass productivity response. Taken together, these results show the value of using a range of approaches as lenses in answering questions of how climate conditions affect vegetation water use and production as a whole, and that in-field sampling adds value to the mechanistic understanding gained by studying the individual components of biodiversity. Future research could usefully build on this platform to develop a fuller picture of the interplay between these components of plant biodiversity, and how they contribute to the resilience of overall productivity under climatic variability and ongoing change.