Landscape change in the lower Omo valley, southwestern Ethiopia: burning patterns and woody encroachment in the savanna

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.