Umgeni Vlei is located 20 km due south-west of Nottingham Road in the KwaZulu-Natal midlands. The main vlei is about 300 ha in extent, and is underlain by Karoo dolerite. It lies at an altitude of 1,840 m, with the highest hill in the reserve at 2,081 m. The vlei functions as a large sponge that is the source of the Umgeni river. The centre of the vlei has extensive areas of Carex marsh, with a ‘hummock-depression’ structure in places, intermixed with Cyperus, Pycreus and Juncus, and submerged vegetation such as Lagarosiphon and Utricularia. The grassland surrounding the vlei is an example of highland sourveld.
See Box for key species. The extensive vlei is good for cranes (Gruidae), and both Grus carunculatus and Balearica regulorum regularly breed there. It is the premier site in South Africa for Grus carunculatus—up to six pairs have nested in the main vlei, with four others nesting in four smaller vleis, all within the reserve boundary. At least two pairs of Balearica regulorum and one pair of Grus paradisea are also present in the IBA, the latter in the grassland surrounding the vlei, which also supports several other species of threatened bird, including Anthus chloris. The vlei could potentially support Sarothrura ayresi. Cisticola brunnescens forage and breed in the flooded grassland adjacent to the vlei. The rocky terrain at higher altitude supports Geocolaptes olivaceus, Saxicola bifasciata, Monticola explorator and Chaetops aurantius. Both Gyps coprotheres and the rare but widespread Gypaetus barbatus are regular visitors to the area.
Non-bird biodiversity: None known to BirdLife International.
Pressure/threats to key biodiversity
The site has been little modified in the past, having been used only for cattle and sheep-grazing. A proposal to develop some of the surrounds for agriculture in the early 1980s precipitated the acquisition of the site by NPB in 1987, in order to protect Grus carunculatus. Cattle are currently excluded from the reserve, probably to the detriment of the cranes. Typically only 5–6 pairs nest there now, and consideration must be given to allowing controlled grazing again, since cattle create some structural diversity in the vegetation that appears to benefit cranes. Apart from its biodiversity value, Umgeni Vlei is a valuable water-catchment area, supplying as it does the Umgeni river, which supports a substantial proportion of South Africa’s gross national product, and the whole of the catchment above the vlei is now conserved, either within the reserve or in a Natural Heritage Site.