Mendip Communications Ltd Job ID: BIO1----0055-1 383 - 55 Rev: 18-04-96 PAGE: 1 TIME: 15:40 SIZE: 57,02 OP: XX Biodiversity and Conservation 5, 55–73 (1996) Patterns of endemism in the limestone flora of South African lowland fynbos CHRISTOPHER K. WILLIS Botany Department, University of Venda, Private Bag X5050, Thohoyandou, South Africa RICHARD M. COWLING* Institute for Plant Conservation, Botany Department, University of Cape Town, Rondebosch 7700, South Africa AMANDA T. LOMBARD FitzPatrick Institute, University of Cape Town, Rondebosch 7700, South Africa Received 15 November 1994; revised and accepted 8 February 1995 Taxonomic and biological aspects of endemism and Red Data Book status were studied amongst the limestone endemics of the lowland fynbos in the Cape Floristic Region, South Africa. Of the 110 limestone endemics, 1.8% are widely distributed in the Cape Floristic Region and 56.4% are regional endemics. Relative to flora of non-limestone lowland fynbos (n = 538 species), the families which were overrepresented in terms of limestone endemics included the Ericaceae, Fabaceae, Polygalaceae, Rutaceae and Sterculiaceae. The Restionaceae was the only underrepresented family. The local limestone endemics were not significantly different from regional endemics in terms of their biological attributes. An analysis of the frequency of the biological traits associated with the limestone-endemic flora established a biological profile for a limestone endemic: a dwarf-to-low shrub with soil-stored seeds which are ant or wind dispersed. In terms of the species richness of limestone endemics, the De Hoop Nature Reserve was the ‘hotspot’ within the region. Relative to the total species richness, the Hagelkraal and Stilbaai areas contained higher-than-predicted numbers of rare species. These areas require urgent attention if the unique floral diversity associated with limestone substrata within the Bredasdorp–Riversdale centre of endemism is to be conserved. Keywords: Cape Floristic Region; lowland fynbos; limestone; endemism; conservation. Introduction Within the south-western corner of Africa, the Cape Floristic Region (CFR) represents the smallest of the six floral kingdoms of the world (Takhtajan, 1986). Covering some 0.04% (89 000 km2) of the earth’s surface, it contains c. 8550 species of vascular plants, of which 73% are endemic to the CFR (Moll, 1990). Of the 957 genera, 198 are endemic and seven families (namely the Lanariaceae, Penaeaceae, Grubbiaceae, Roridulaceae, Retziaceae, Stilbaceae and Geissolomataceae) are endemic. The CFR is dominated by fynbos, a sclerophyllous, heath-like shrubland associated with nutrient-poor soils which *To whom correspondence should be addressed. 0960-3115 q 1996 Chapman & Hall Mendip Communications Ltd Job ID: BIO1----0056-1 383 - 56 Rev: 18-04-96 PAGE: 1 TIME: 15:40 SIZE: 55,10 OP: XX 56 Willis et al. cover most of the region (Cowling and Holmes, 1992a). These shrublands are fire-prone and usually burn at six to forty year intervals (Cowling and Holmes, 1992b). The coastal lowland areas of the CFR represent one of the most threatened regions of natural vegetation because of intensive agriculture, urbanization and alien-plant encroachment (Jarman, 1986). Amongst the lowland flora, limestone fynbos communities are particularly vulnerable, because of their edaphic specialization and restricted nature and they contain many threatened endemic species (Hilton-Taylor and Le Roux, 1989). Despite the flora being relatively well studied, patterns and determinants of endemism have been poorly examined in the CFR (Cowling and Holmes, 1992a). For conservation management, it is important to know whether or not an endemic flora constitutes a random assemblage with respect to taxonomy, habitat preference and biological attributes. If not, then the peculiar characteristics of the endemic flora can be used as a guide for management. Unfortunately, studies that seek to characterize endemics in terms of these attributes represent a major gap in the literature for all endemic-rich areas (Cowling et al., 1992). Although certain studies in the lowland floras of the CFR have shown that most endemics are edaphic specialists and that certain substrata (for example, limestone) harbour disproportionally high numbers of endemics (Cowling and Holmes, 1992a; Cowling et al., 1992), no studies have looked at these edaphic specialists per se. This study therefore represents the first attempt to analyse and characterize endemic vascular plants restricted to limestone substrata within the Cape lowland flora. Based on the distributions of limestone endemics within the lowland flora, J.P. Willis et al. (in press) have attempted to determine the ideal configuration of reserves for their conservation. We addressed the following questions. (i) How many limestone endemics are there? (ii) How many of these species are widespread within the CFR, or are endemic at the regional and local scales? (iii) How many endemics are listed in the Red Data Book? (iv) What are the patterns of species richness across the landscape? (v) Do the limestone endemics differ in terms of taxonomic and biological traits from non-limestone flora in the Cape lowlands? (vi) Do local limestone endemics differ from more widespread limestone species in terms of these traits? Study area Geology, geomorphology and soils The study area comprises a gently rolling, coastal lowland landscape towards the southern tip of Africa from Hermanus in the west to the Gouritz River in the east, and it includes both the Agulhas (Cowling et al., 1988) and Riversdale coastal plains (Rebelo et al., 1991). See Fig. 1. As the entire area was inundated by transgressions during the mid-Miocene (15 Myr (million years)) and the early–mid-Pliocene (4 Myr), most sediments and soils postdate the regression (Hendey, 1983). Despite the low topographical diversity when compared with the mountainous regions of the fynbos biome, the area has numerous contrasting soil types and land systems (Thwaites and Cowling, 1988). Table Mountain Group sandstones and quartzites, Bokkeveld Group shales, limestones, remnant silcrete and ferricrete outcrops and calcareous coastal dunes are all represented in the area. Miocene–Pliocene limestones and associated colluvial deposits of the Bredasdorp Group form distinctive relief features in the coastal zone, and soils on the limestone bedrock are shallow, well-drained, calcareous sands (Cowling and Holmes, 1992a). The Riversdale Plain, defined as the coastal plain south of the Langeberg Mountains between the Mendip Communications Ltd Job ID: BIO1----0057-1 383 - 57 Rev: 18-04-96 PAGE: 1 TIME: 15:40 SIZE: 55,10 OP: XX Patterns of endemism in the limestone flora of lowland fynbos 57 Duiwenhoks River in the west and the Gouritz River in the east, contains the largest development of Tertiary limestone in the fynbos biome. Further details on the geomorphology, geology and soils of the area are given by Malan (1987), by Thwaites (1987), by Rogers (1988) and by Thwaites and Cowling (1988). Climate The climate of the area is relatively uniform. The average annual temperature is in the range 15–17.48C, depending on the locality. Along the coast, the mean annual rainfall ranges from 454 mm at Gansbaai to 400 mm at the Gouritz River mouth. Higher values would be recorded in the hills but data are lacking. Rainfall seasonality is typical of a Mediterranean-type climate, with most of the annual precipitation falling in the winter months. Limestone fynbos The study was conducted in the Bredasdorp–Riversdale centre of endemism (BRC) (Cowling et al., 1992), a well-defined centre for the calcicole fynbos taxa confined to the Bredasdorp Formation limestone and associated colluvial deposits which have their maximum exposure in this area (Fig. 1). The term used to describe the vegetation associated with limestone in the BRC has varied according to the classification used. Moll et al. (1984) described the vegetation as ‘limestone fynbos’, whereas Cowling and Holmes (1992b), based on Campbell’s (1985) use, classified the vegetation as ‘proteoid fynbos’. Leucadendron meridianum I.J. Williams and Protea obtusifolia Bueck ex Meissner dominate the limestone areas within the proteoid fynbos, with Leucospermum truncatum (Bueck ex Meissner) Rourke and Leucodendron muirii E. Phillips co-dominant in this community where limestone outcrops have skeletal soils (Rebelo et al., 1991). We regard the vegetation endemic to limestone substrata as limestone fynbos. Fifty-four per cent (1100 km2 of the 2030 km2) of the limestone fynbos occurs in and immediately adjacent to the Riversdale coastal plain (Moll et al., 1984; Bohnen, 1986). Details of other vegetation categories in the area are given by Cowling et al. (1988) and by Rebelo et al. (1991). Methods Categories and centres of endemism Three categories of endemism were recognized in the BRC: (i) CFR endemics confined to the CFR; (ii) regional endemics confined to Weimarck’s (1941) South Western Centre and the BRC (Fig. 1) (Cowling, et al., 1992); and (iii) local endemics, arbitrarily recognized as taxa confined or nearly confined to subcentres (such as the Bredasdorp Centre) within the BRC (Weimarck, 1941; Midgley, 1986; Oliver et al., 1983). All of the local endemics considered in this study occupy ranges of less than 2000 km2 (2.2% of the Cape Floristic Region); some ranges are less than 5 km2. Data collection Data on the distribution of the vascular-plant taxa (species and intraspecific variants, henceforth referred to as species) endemic to limestone substrata in the