In every debate about the validity and utility of the hotspot concept, there has been consensus on one issue – that the Cape Floristic Region is the hottest of them all. So what are the hot-spot criteria?
First, a hot spot is assessed in terms of three measures of its species diversity: the number of species within a homogeneous community; the amount of change, or turnover, in species composition across a gradient; and the change in species composition within similar habitats but in different geographical locations, such as on neighbouring mountain peaks. A walk up the mountain backdrop to Kirstenbosch will illustrate how rapidly plant species composition changes, from one small community dominated by proteas, to another dominated by ericas, or to the restio communities in the moist bogs of the summit. If one spends a day listing species on the plateau of the Table Mountain summit, followed by a day in similar mountain fynbos just across the Cape Flats, in the Hottentots
Round Trip To Kirstenbosch National Botanical Garden Photo Gallery
Holland Mountains, one might find less than a 50 per cent similarity in the species of these two sites, each of which, at first glance, presents the same rather dull, olive-green heathland appearance.
High biodiversity occurs where all three measures are simultaneously high. The clearly delimited 470 square kilometres of the Peninsula had, at last count, 2 285 species of fern and flowering plant, of which more than 150 occur nowhere else in the world. A comparison can be made with the flora of the United Kingdom, which has an area of 308 000 square kilometres, with just 1 472 native species, only 20 of which are endemic. Table Mountain National Park, covering an area similar to that of Greater London, has 1 470 species – equal to that of the whole of the UK, in the area of just one city. Even the Amazon Basin, famously rich in species across its many-layered forests, has only one third as many species per 10 000 square kilometres as does the fynbos.
The Red List of South African Plants, 2009, sounds a warning about species loss in the region. The Red List of South African Plants 2009 includes the contributions of 169 botanists, brought together by an editorial team competently led by SANBI’s Domitilla Raimondo.
The new list sounded a warning: of the 20 456 species assessed, of which 13 265 (65 per cent) are endemic to South Africa, 2 577 species were considered in danger of regional or global extinction. A further 2 232 are listed in other categories of conservation concern, giving a total of 4 809 species, or 23.5 per cent of the flora – one in every four South African plants – in some level of danger.
The good news – if it can be called such – is that of the 59 species believed to have gone extinct in an earlier (1996) survey, no fewer than 18 have been rediscovered in the course of the latest survey programme. But in many cases these rediscovered species are represented by very small populations – representing, in effect, ‘the living dead’. The really bad news is that the total number of species listed as Extinct or Possibly Extinct has increased from 59 to 116, a 96 per cent increase since 1996.