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Study area and data
The data we used were records of all naturalised alien plant species from the National Herbarium, Pretoria Computerised Information System (PRECIS), for Namibia, Botswana, South Africa, Lesotho and Swaziland. Distribution records in PRECIS are currently most complete for these southern African countries (Steenkamp et al., 2005) and of these, South 2. Southern African Alien Phytogeographic Regions Africa, Lesotho and Swaziland provide the best data. Analyses were conducted at the quarter degree square resolution because PRECIS data are mainly available at this resolution.
The species rank was the lowest taxonomic level which was analysed: records of differen infraspecific taxa were pooled and hybrids were not considered. Ultimately, 861 alien plant species were included in the analysis.
Southern Africa is a geologically and climatically diverse region. Notable drivers of floristic composition are the topographical and geological variation between the interior plateau of relatively high altitude, that is bordered on three sides by mountain ranges forming the Great Escarpment, beyond which is a sharp drop in altitude towards the coastal plains (Fig. 1; Steenkamp et al., 2005; Mucina & Rutherford, 2006). Notable climatic drivers include a strong moisture gradient from arid regions in the west to humid regions in the east, and a variation in the seasonality of rainfall, from summer rainfall comprising most of southern Africa, to a smaller winter rainfall area in the west, and year-round rainfall on the south-west coast between the winter and summer rainfall areas (Steenkamp et al., 2005; Mucina & Rutherford, 2006). Finally, eight biomes have been described for South Africa, the grassland, savanna, Albany thicket, Nama-Karoo, succulent Karoo, forest, fynbos and Indian Ocean coastal belt (Fig. 1; Mucina & Rutherford, 2006). The Nama-Karoo, succulent Karoo and savanna biomes continue north into Namibia, which also includes the desert biome (Irish, 1994; Van Wyk & Smith, 2001). Botswana is mainly covered by savanna biome with a smaller area of Nama-Karoo (Van Wyk & Smith, 2001; Ringrose et al., 2002).
Chapter 1: General Introduction
Chapter 2: Alien Phytogeographic Regions of Southern Africa: Numerical
Classification, Possible Drivers, and Regional Threats
Chapter 3: Are Environmental Transitions More Prone to Biological Invasions?
Chapter 4: Patterns of Beetle and Spider Richness and Composition Across a South
African Savanna-Grassland Ecotone.
Chapter 5: General Discussion
Appendix 1: Supporting information for Chapter 2.
Appendix 2: Supporting information for Chapter 3
Appendix 3: Supporting information for Chapter 4.
