Impact of bush encroachment on African Savannah rangelands in the face of climate change and variability.
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Date
2024
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University of the Western Cape
Abstract
In the African continent, especially in the southern part of the continent, climate change has been associated with significant changes in temperature and precipitation patterns. Some of the signs of climate variability noted in Southern Africa are low and erratic precipitation that leads to drought, along with increases in temperature. Due to the climate variability, terrestrial ecosystems such as savannah rangelands have been adversely affected which has led to the disruption of ecosystem services and spatial configuration. For example, studies have shown that rainfall variability in the arid savannah regions is the primary determinant of the rate of bush encroachment. In rangelands, climate change has a significant impact on the transition from grass-dominated species to woody species, which is influenced by the specific weather patterns in the area. In this regard, it is pivotal to understand the rate of bush encroachment within the savannah rangelands of South Africa. The impact of bush encroachment on savannah rangelands amid climate variability in (un)protected areas remains under explored, despite extensive works in bush encroachment in general. In order to gain a thorough understanding of how environmental changes affect the growth of bushes, both in untouched landscapes and in human-manipulated environments.
The main aim of this study was to assess the utility of remotely sensed data in detecting and mapping the extent of bush encroachment in the African savannah rangelands in the face of climate change and variability. To address the overarching aim of this study, four specific objectives were set. Firstly, a review of literature on advancements in satellite sensing of the impacts of climate and variability on bush encroachment in savannah rangelands was conducted. Based on the results of objective one, it is evident that there is a knowledge gap regarding the impact of climate variability on rangelands that has to be fully explored using remotely sensed data. The second objective assessed the distribution of native invasive woody plants co-existing with native savannah rangeland. The findings from objective two showed that native invasive species occupy 63.3% of the area covered in contrast to the 18.3% of the native species found within the study area. The overestimation of the native invasive species was a result of the spectral similarities, comparable ecological composition, and the challenge of identifying native vegetation with Sentinel imagery, which may have led to confusion between native and native invasive species as indicated by the error metrics. The third objective evaluated the influence of climate variability on bush encroachment in both protected and non-protected areas over 30 years using Landsat archive data. The results from objective three shows that seasonal climatic variability also influenced the rapid increase of native invasive plants. Furthermore, the findings of this study suggested that the spatial extent of native invasive species has increased significantly between 1992 and 2022. The findings of the study demonstrated that the variability of precipitation, topography, and temperature within an annual period regulate the rate of bush encroachment in (un)protected areas. The final objective modelled the potential distribution of bush encroachment under different climate change scenarios. The results show a considerable disparity between current and future climate scenarios distributions of woody native invasive species. Overall, the predicted species distribution showed that native woody invasive abundance will increase, giving future climate scenarios using the maximum atmospheric carbon Representative Concentration Pathways (RCP) 8.5 for 2080. However, in contrast to the predicted species distribution using the minimum atmospheric carbon Representative Concentration Pathways (RCP) 2.6, which show a decrease in the abundance of encroachment by 2080. In summary there is a variation in the occurrence and distribution of bush encroachment of the estimated suitable areas across all models. The findings of this study offer comprehensive understanding of the historical, current and potential patterns of bush encroachment. Also, these findings underscore the critical need for proactive management strategies to mitigate bush encroachment, particularly under high-emission scenarios, ensuring the sustainability of semi-arid savannah rangelands in the face of climate change.
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Keywords
Bush encroachment, Climate change and variability, African savannah rangelands, Native invasive species