The Overberg is the region of the Western Cape in South Africa situated at the southern extremity of the African continent. It is bordered by the Hottentots Holland mountains in the west and extends to Cape Infanta at the mouth of the Breede River. To the north it is bordered by the Riviersonderend and Langeberg mountain ranges and it includes the districts of Caledon, Bredasdorp and Swellendam. It is literally over the mountains, east of Cape Town. The shores are washed by the Indian and Atlantic oceans which meet at Cape Agulhas, the southern most tip of the continent.
The Overberg has a typical Mediterranean climate with mild, wet, winters and warm to hot, dry summers. Rainfall varies from 300 to 1000 mm per annum depending on the topography with the highest precipitation occurring near the coast and on the south facing mountain slopes. About 20% of the rainfall comes in summer. The mountain ranges consist of ancient Table Mountain Sandstone (quartzites) giving rise to sandy, acid soils low in nutrients. Between the coastal and inland mountains is a wide undulating plain consisting of shale and clay deposits which are fertile and suitable for intensive agriculture. The coastal plain consists of recent marine deposits from which limestone has been formed, resulting in sandy, alkaline soils.
The Overberg is the heart of the Famous Cape Floral Kingdom mainly comprising the well known Fynbos vegetations (fine-leafed shrubland). Although it is the smallest of the plant kingdoms in the world, it is the richest with an amazing 9000 species of which about 70% are endemic. Different types of Fynbos occur in the different habitats - the mountain fynbos being dominated by Proteas, Ericas and Restios. The fynbos vegetation that occurs on the shale and clay soils is called Renosterveld after the dominant species, the Rhinocerus bush (Elytropapus rhinocerotis). This area is particularly rich in bulbous plants. A third distinctive form of fynbos occurs exclusively on the limestone and dune soils of the Agulhas coastal plain.
Bulbs occur in all three types of fynbos vegetation, each having a number of distinctive species. The Iridaceae are the most spectacular with large numbers of Gladiolus, Moraea and other species. Hyacinthaceae and Amaryllidaceae are well represented with some rare endemics occurring in the region. The Renosterveld has the richest and most diverse bulbous flora, but because it has been so extensively cultivated only about 7% of the original vegetation survives and many species are under severe threat. Occasional fires are a natural occurrence in the region and most species are adapted to fire. Some bulbous plants, like Lachenalia sergeantii, are dependent on fire to flower. In spring after a fire an amazing explosion of flowering of bulbous plants occurs. The spread of alien vegetation, especially of Australian acacia species and pines on the mountains, is a very severe threat to the survival of much of the Fynbos and attempts to control its spread have been very ineffective.
This information furnished by Cameron McMaster.