IMPACTS OF TSETSE CONTROL AND LAND-USE ON VEGETATIVE STRUCTURE AND TREE SPECIES COMPOSITION IN SOUTH-WESTERN ETHIOPIA

1. More effective control of the tsetse fly in Africa will reduce cons traints imposed by the livestock disease, trypanosomiasis. Trypanosomi asis lowers livestock productivity, and in some areas, may limit the a bility of farmers to keep livestock and plough the land using animal t raction. Control of the disease may cause the expansion of livestock p opulations and cultivated land area which, in turn, may have negative impacts on ecosystem structure and function. 2. The objective of this study was to assess the impacts of tsetse control, through expansion o f agricultural land-use. on vegetative structure and tree species comp osition in the Ghibe Valley, south-western Ethiopia. This was done by first describing land cover/land-use patterns in areas with and withou t tsetse flies, and then quantifying land-use impacts on vegetation. 3 . Land-use/land cover was assessed and quantified by classifying a rec ent LANDSAT Thematic Mapper (TM) image of the valley and analysing the abundance of cover types in a geographical information system (GIS). Vegetative structure and tree species composition were measured in fie ld plots in two types of cultivated fields (oxen and tractor-ploughed) , and in upland wooded grasslands and riparian woodlands. 4. Land cove r in the Ghibe Valley was dominated by wooded grasslands (60%) and cul tivation (26%), with smaller patches of dense upland woodland (9%) and sparse woodland strips along river courses (3%). Most farms were cult ivated by smallholders using oxen (25% of the total cultivated area) w ith limited areas ploughed by large holders using tractors (0.5%). 5. The cover of woody plants was highest in riparian woodlands (53%), mod erate in oxen-ploughed fields (6%) and wooded grasslands (9%), and low est in tractor-ploughed fields (1%). Species diversity (Shannon index - H') was greatest in riparian woodlands (1.6) and smallholder fields (1.4), moderate in grasslands(1.0) and low on largeholder farms (0.7). 6. These results highlight the importance of rare but biologically ri ch riparian areas, which should be a focus for conservation. If tsetse control, through the expansion of cultivation causes degradation of t hese woodlands, the potential for impact is high. 7. However, there ap pear to be few changes in the vegetation in the process of conversion of wooded grasslands into smallholder fields, which is the likely resu lt of successful tsetse control. A hypothetical model of vegetative ch ange in the Ghibe Valley is described in the light of the vegetative p otential of the area and recent changes in the frequency of hunting an d burning in the valley.