Summary1. Shrub encroachment has been widely observed in savanna regions. This study analysed the causes of shrub encroachment in the lowveld savanna of north-eastern Swaziland, southern Africa, and highlighted management regimes that can be used to reduce or prevent it. 2. The rates and dynamics of shrub encroachment were quantified for the period 1947-90 using aerial photographs, and for 1997 using a ground survey. Five similar areas with different land-use histories were compared to investigate the relative importance of fire, herbivory, rainfall, soil type and shrub density in driving shrub dynamics. 3. In the study area as a whole, shrub cover increased from a mean of 2% in 1947 to 31% in 1990. Dichrostachys cinerea accounted for most of the increase in cover, contributing 81% to total shrub cover during 1997. Shrub cover was strongly correlated with shrub density and weakly negatively correlated with tree cover. 4. Shrub encroachment varied across land-use fence lines. The key determinants of shrub dynamics were grazing, through its negative effect on fire frequency and an interaction between drought frequency and high shrub cover. Browsing pressure had a significant but minor impact on dynamics, while soil type had no significant effect. High grazing pressures through their effect on fire frequency were critical throughout the study period in promoting shrub encroachment, while the interaction between drought and high shrub cover produced declines in the later stages. Browsing had an impact on encroachment only in the early stages. 5. Frequent fires, facilitated by low grazing pressures, were capable of preventing shrub encroachment. When coupled with drought, frequent fires could reduce high shrub densities. 6. As cover and density were strongly correlated, it can be inferred from the negative correlation between change in cover (density) and initial cover (density) that the rate of shrub encroachment was cover (density)-dependent and that there was a shrub equilibrium of 40% cover, approximating to 2400 plants ha -1 . Shrub population growth was driven by events (fire, drought) as well as continuous agents (density dependence, mean browsing and grazing pressure). 7. Bush encroachment can be reversed by a combination of management (frequent fires) and climatic events (drought). The implications for savanna management are discussed.

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The Blue Swallow Hirundo atrocaerulea is a globally threatened species endemic to sub-Saharan Africa. The total population breeding south of the Limpopo River (i.e. in South Africa and Swaziland) probably numbers around 100 pairs. A significant proportion of these birds breed in Swaziland, but to date little has been published on this population. Suitable breeding habitat has been reduced significantly in the country in recent decades, due mostly to afforestation with exotic timber plantations, with urbanization playing a lesser role. In Swaziland, breeding sites are restricted to grasslands above 1,200 m, but mostly above 1,300 m. Timing of egg laying is bimodal indicating double brooding. The number of nests initiated in a season is weakly correlated with rainfall in preceding months. Nests were built predominantly in disused antbear Orycteropus afer burrows, with smaller numbers in natural sinkholes. Mean clutch size was 2.80, and 61% of eggs laid resulted in fledged offspring. Mean productivity was 1.30 fledglings per pair per nest attempt. These figures suggest that breeding success is not currently being reduced in Swaziland. The minimum total population currently thought to be breeding in Swaziland is 10 pairs, but this is based on intensive studies of only part of the suitable range. It is recommended that a complete survey be conducted covering the entire range of the species in Swaziland.

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