The Wood vegetation of the proposed Stiegler's Gorge Reservoir, South - East Tanzania

The plans to develop hydropower at Stiegler’s Gorge date from German colonial era in Tanzania when several expeditions were made to investigate the Rufiji River Basin. In 1975 the Tanzania Government established the Rufiji Basin Development Authority (RUBADA), charged with the construction and operation of hydro-works in the Rufiji Basin as well as the promotion of general development of the entire basin. The dam will give a reservoir of about 1,500 sq.km. This study, which evaluates the vegetation within the planned reservour, is one of many aimed at providing RUBADA with information needed in the planning, construction and operation of the project. The vegetation of the study area was mapped from aerial photos and field work provided information on species composition and size classes. Multi-stage stratified sampling was adopted during field work and the point-centred quarter (PCQ) technique was used. The technique gave distance data that were used in the determination of absolute densities. The Miombo woodland formation was shown to occupy the whole study area although an analysis of the vegetation associations showed that the typical dominants of miombo, i.e. Brachystegia spiciformis and Julbernardia globiflora are few. Past human settlements are thought to have had serious effects on the distribution and composition of the vegetation mainly through the use of fire and shifting cultivation which were practised by the inhabitants. As a result most parts of the study area are wooded grassland which accounts for 60% of the total area. Population estimates have shown that there are 13.1 million trees of which 43.5% are in wooded grassland and 56.5% in other vegetation types. Commercial species account for 38.1% of the trees. There are 57.5% million shrubs, 54.9% of which are in wooded grassland. For the commercial species not all individuals are exploitable because some do not possess the exploitation size requirements and/or are damaged by fire and elephants. The results of this study indicate that total vegetation clearing of the reservoir before river impoundment is not recommended. Selective clearing is justified in isolated areas. However, drawing up of the criteria for clearing requires consideration of other factors apart from those pointed out in the text.