Abstract
African savannas are increasingly affected by woody encroachment, an increase in the density of woody plants. Woody encroachment often occurs unexpectedly, is difficult to reverse, and has significant economic, cultural and ecological implications. The process of woody encroachment represents a so-called regime shift that results from feedback loops that link vegetation and variables such as fire, grazing and water availability. Much of the work on woody encroachment has focused on the direct drivers of the process, such as the role of fire or grazing in inhibiting or promoting encroachment. However, little work has been done on how ecological changes may provide feedback to affect some of the underlying social processes driving woody encroachment. In this paper, we build on the ecological literature on encroachment to present a qualitative systems analysis of woody encroachment as a social-ecological regime shift. Our analysis highlights the underlying indirect role of human population growth, and we distinguish the key social-ecological processes underlying woody encroachment in arid versus mesic African savannas. The analysis we present helps synthesize the impacts of encroachment, the drivers and feedbacks that play a key role and identify potential social and ecological leverage points to prevent or reverse the woody encroachment process.
Highlights
Woody encroachment has been a problem in both southern African savannas [1] and globally for over a century [2], and appears to be increasing in many regions [3,4]
The objective of this paper is to review woody encroachment in African savannas using a social-ecological regime shift lens
We developed a conceptual model of the main ecological and social processes underlying woody encroachment in African savanna systems (Figure 4)
Summary
Woody encroachment has been a problem in both southern African savannas [1] and globally for over a century [2], and appears to be increasing in many regions [3,4]. Savannas are home to 505 million people in Africa, most of whom rely directly on these ecosystems for their livelihoods [7]. Woody encroachment threatens the provision of ecosystem services such as food and clean water, grazing for livestock farming, and habitats for some of the world’s last remaining mega herbivores [6,8,9]. There is growing consensus that managing anthropogenic impacts on ecosystems and the services they provide requires a better understanding of the interactions between ecological and social systems [10]. Much of the research on woody encroachment has focused on ecological drivers, especially the impact of disturbance (e.g., fire and grazing) and water availability on tree establishment and persistence [11–14]. Few papers explicitly consider the role of social processes underlying these ecological changes, or how ecological changes can provide feedback to affect the underlying social processes. We build on the ecological understanding of woody encroachment, to develop a broader social-ecological understanding of the dynamics underlying woody encroachment
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