Namaqualand, South Africa - An overview of a unique winter-rainfall desert ecosystem
Namaqualand is a winter-rainfall desert of some 50 000 km2, located in north-western South Africa. For a desert ecosystem, the region is characterized by a unique selective regime, namely highly predictable annual rainfall and a moderate temperature regime throughout the year. This selective regime is responsible for the unique plant ecological features of Namaqualand. These include: the dominance of communities by dwarf to low, shallow-rooted, short-lived and drought-sensitive leaf succulent shrubs; high abundance and diversity of geophytes; winter growth phenology; regular and spectacular spring flowering displays; rapid population turnover of perennials; weak competitive interactions; and high local and regional plant diversity. This paper provides a physiographical, biogeographical and ecological overview as background to this special issue. First, we outline the physiography and climate of Namaqualand, emphasizing unique components of its selective regime. Next we discuss the region's phytogeographical and floristic characteristics. Then we summarize what is known about plant form and function, focusing on growth form mix, phenology, carbon gain, water relations, and reproduction in vegetation dominated by leaf-succulent shrubs. Finally, we interpret Namaqualand's uniquely rich and dynamic plant communities in terms of plant functional processes. These plant ecological patterns and processes are discussed in terms of the predictions of a simple conceptual model for succulent-rich communities.