Advancements in the satellite sensing of the impacts of climate and variability on bush encroachment in savannah rangelands

Abstract

An increase in shrubs or woody species is likely, directly or indirectly, to significantly affect rural livelihoods, wildlife/livestock productivity and conservation efforts. Poor and inappropriate land use management practices have resulted in rangeland degradation, particularly in semi-arid regions, and this has amplified the bush encroachment rate in many African countries, particularly in key savannah rangelands. The rate of encroachment is also perceived to be connected to other environmental factors, such as climate change, fire and rainfall variability, which may influence the structure and density of the shrubs (woody plants), when compared to uncontrolled grazing. Remote sensing has provided robust data for global studies on both bush encroachment and climate variability over multiple decades, and these data have complemented the local and regional evidence and process studies. This paper thus provides a detailed review of the advancements in the use of remote sensing for the monitoring of bush encroachment on the African continent, which is fuelled by climate variability in the rangeland areas. An understanding of how bush encroachment is fuelled by climate variability and change, as well as its impact on rangelands in the semi-arid areas, is still limited due to the scanty and, at times, fragmented research, especially when it comes to using remote sensing technology. This study also highlights the scientific knowledge gap that exists regarding the impact of climate variability on rangelands, which has yet to be explored by using remotely-sensed data. From a remote sensing viewpoint, rangeland monitoring is challenging when it comes to discriminating between the different herbaceous layers and implementing management practices. Overall, this review emphasizes the increasing role and potential of remote sensing in tracking the impact of climate change on savannah rangelands.