Time Series Monitoring of Bush Encroachment by <i>Euclea divinorum</i> in Ol Pejeta Conservancy Laikipia, Kenya

Abstract

Abstract:Bush encroachment refers to the invasion of woody species in Savannah ecosystems driven by either anthropogenic and/or natural factors. This study sought to examine land cover changes and topographic features attributable to patterns of encroachment in Ol Pejeta Conservancy (OPC) where, Euclea divinorum unpalatable woody species has colonised former grasslands and other habitats which provide grazing grounds for herbivore wildlife species. Here, we monitored vegetation cover trends in the period 1987-2016 using five vegetation classes on Landsat images acquired during the dry season. Additionally, slope based NDVI maps and digital elevation models were used to identify topographic influences on vegetation change. Results revealed that E. divinorum increased significantly between 1987 and 2016 (Mann Kendall test for trend analysis tau 1, n=6, p< 0.01). On the other hand, Acacia drepanolobium and Acacia xanthophloea decreased from 49.72% and 5.31% in 1987 to 17.00% and 0.29% in 2016 respectively. Further, areas in low elevation were more colonised by E. divinorum. The colonising E. divinorum is unpalatable hence lacks natural predators whilst, A. drepanolobium and A. Xanthophloea which are alternative herbivory species decreased. Understanding dynamics of woody vegetation in savannah is crucial for management of healthy and sustainable ecosystems.

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

“…Although these studies have broadened the understanding and scope of the bush encroachment phenomenon, from its impact on the ecology to its impact on carbon sequestration (Stafford et al, 2017), there has been no correlation between bush encroachment and climate variability in rangeland areas, especially by using remotely-sensed data. However, some studies have used remote sensing to compare the biodiversity between the protected savannah rangeland and the adjacent non-protected farmland in the southern Kalahari (Munyati et al, 2011;Mutunga, 2018). There are some gaps that still need to be explored with regard to the impact of climate variability on rangeland bush encroachment, especially in southern Africa.…”

“…Given the observed trends in precipitation seasonality, droughts and land use in East African countries, this is expected to change in the future; therefore, monitoring techniques, such as the deployment of hyperspectral and multispectral sensors, are used to improve our understanding of the potential impacts of land-use changes on the ecosystem services in the East African rangelands. It has been observed that Kenya has a high rate (39%) of bush encroachment in the rangeland areas, with the severe impact being felt in both the protected and unprotected areas, which changes the livestock grazing habits and conservation benefits (Mutunga, 2017(Mutunga, , 2018.…”