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Abstract
In this article we examine bush encroachment in a savanna ecosystem of the lower Omo Valley occupied by Mursi agro-pastoralists. Focusing on the role of fire and grazing, the main anthropogenic disturbance factors in the savanna, we compare the results of our ecological surveys with Mursi perceptions and understandings of environmental change. The main change described by Mursi is the loss of grassland over the last 30 to 40 years. Their explanations centre on three complementary factors: a growth in human and livestock numbers, leading to a reduction in grass availability; a tendency towards more permanent settlement, leading to heavy year-round pressure on certain grazing areas; and the loss of traditional burning practices, leading to frequent small fires rather than infrequent large blazes, capable of clearing the savanna of trees. In addition, state encroachment in general and the establishment of the Omo and Mago National Parks in particular have restricted mobility and reduced the actual and potential grazing area available to Mursi livestock. Our ecological surveys did not, however, show a causal relationship between fire, grazing and encroachment pattern. We therefore suggest that grazing and burning practices should be considered relevant, but not necessarily the most important, factors explaining bush encroachment in this case.
Acknowledgements
This article is one of the outcomes of research project A/H E510590/1, “Landscape, People and Parks: environmental change in the Lower Omo Valley, southwestern Ethiopia”, funded by the Arts and Humanities Research Council of the United Kingdom, under its “Landscape and Environment” programme. We are grateful to the people of Dargus, Maganto and Mako for generously sharing their knowledge and experience; to Olisarali Olibui for his equally vital work as translator; and to two reviewers for the Journal of Eastern African Studies for their very helpful comments on the manuscript.
Notes
1. Homewood, Ecology of African Pastoralist Societies.
2. Little, “Pastoralism, Biodiversity and the Shaping of Savanna.”
3. Vetter, “Rangelands at Equilibrium”; Homewood, Ecology of African Pastoralist Societies.
4. Wiegand, Ward and Saltz, “Multi-scale Patterns and Bush Encroachment”; Burke, “Savanna Trees in Namibia”; Belsky, “Tree/Grass Ratios in East African Savannas”; Gillson, “Testing Non-equilibrium Theories”; Jeltsch et al., “Tree Spacing and Coexistence”; Sankaran, Ratnam and Hanan, “Tree–grass Coexistence”; Scholes et al., “Trends in Savanna Structure”; Scholes, “Convex Relationships in Ecosystems”; Walker et al., “Stability of Semi-arid Savanna Grazing Systems”; Walter, Natural Savannas; Archer et al., “Autogenic Succession”; Wiegand, Saltz and Ward, “A Patch-Dynamics Approach to Savanna Dynamics.”
5. See discussion in Abule, Snyman and Smit, “Comparisons of Pastoralists Perceptions”; Archer et al., “Autogenic Succession in a Subtropical Savanna”; Asner et al., “Large-scale Impacts of Herbivores on African Savannas”; Coughenour and Ellis, “Landscape and Climatic Control of Woody Vegetation “; Goheen et al., “Consequences of Herbivory by Native Ungulates”; Holdo et al., “Plant Productivity and Soil Nitrogen as a Function of Grazing”; Sankaran et al., “Determinants of Woody Cover in African Savannas”; and Scholes and Archer, “Tree–grass Interactions in Savannas” amongst many others.
6. Angassa and Oba, “Bush Encroachment Control Demonstrations in Southern Ethiopia”; Homewood et al., “From the Cover”; Homewood and Brockington, “Biodiversity, Conservation and Development in Mkomazi Game Reserve”; Oba and Kotile, “Assessments of Landscape Level Degradation in Southern Ethiopia”; Oba et al., “Bush Cover and Range Condition Assessments.”
7. Kloos et al., “Problems for Pastoralists in the Lowlands.”
8. Scott, Seeing Like a State.
9. Nicholson, “The Nature of Rainfall Variability over Africa.”
10. Nicholson, “The Nature of Rainfall Variability over Africa.”
11. Turton, Pastoral Livelihoods in Danger; Turton, “The Mursi and the Elephant Question.”
12. Sankaran et al., “Determinants of Woody Cover in African Savannas.”
13. Van Langevelde et al., “Effects of Fire and Herbivory”; Higgins, Bond and Trollope, “Fire, Resprouting and Variability.”
14. Sinclair et al., “Long-Term Ecosystem Dynamics in the Serengeti”; Dublin, “Vegetation Dynamics in the Serengeti-Mara Ecosystem.”
15. Trollope, “Fire in Savanna,” cited in FAO, Global Forest Fire Assessment, cited in Walters, “The Land Chief's Embers,” 264.
16. Gil-Romera and Sevilla-Callejo, “Bush Encroachment Assessment Based in Point-pattern Models.”
17. Lusigolonyi (Red Boy) is the name given by Mursi to David Turton.
18. Bio-iton-giga plays an important part in the affairs of the northern Mursi, being widely respected as a “jalabai” or influential speaker, and acting as a spokesperson on behalf of the community in such matters as conflicts with the national park authorities.
19. Randall, “African Pastoralist Demography.”
20. Walters, “The Land Chief's Embers.”
21. Walters, “The Land Chief's Embers.”, 117.
22. Walters, “The Land Chief's Embers.”, 192.
23. See, for example, Bollig and Schulte, on local explanations of vegetational change amongst the pastoral Pokot of northern Kenya: “Many elders allege that internal conflicts are at the heart of the problem. The generational conflict between elders and young men, curses inflicted by elders on juniors, and antisocial behaviour in general are rated as probable causes for environmental decline.” “Environmental Change and Pastoral Perceptions,” p. 499.
24. Gil-Romera and Sevilla-Callejo, “Bush Encroachment Assessment Based in Point-pattern Models.”
25. Gillson and Ekblom, “Resilience and Thresholds in Savannas.”
26. Holling, Gunderson and Ludwig, “In Quest of a Theory of Adaptive Change”; Holling, “Understanding the Complexity of Economic, Ecological, and Social Systems”; Holling, “The Resilience of Terrestrial Ecosystems.”
27. Gunderson and Holling, Panarchy.
28. Gil-Romera et al., “Long-term Resilience, Bush Encroachment Patterns and Local Knowledge.”
29. Bird et al., “The ‘Fire Stick Farming’ Hypothesis.”
30. Sullivan, “The Impacts of the People and Livestock in Arid North-west Namibia”; Angassa, “The Ecological Impact of Bush Encroachment in Borana”; Angassa and Baars, “Ecological Condition of Encroached and Non-Encroached Rangelands”; Angassa and Oba, “Herder Perceptions on Impacts of Range Enclosures”; Oba and Kaitira, “Herder Knowledge of Landscape Assessments in Arid Rangelands”; Reid and Ellis, “Impacts of Pastoralists on Woodlands in South Turkana”; Sullivan and Konstant, “Human Impacts on Woody Vegetation, and Multivariate Analysis.”
31. Connectivity refers to the level of interaction between the elements of an ecosystem. This is typically low in arid savannas, which means that the system is able to recover relatively quickly following a disturbance, since the alteration will affect a relatively small number of elements.