A preliminary account of patterns of endemism in Namibia's Sperrgebiet - The succulent karoo

Abstract

Aim: This study investigated spatial patterns of endemism in the flora of Namibia's succulent karoo in order to generate information for conservation planning. Location: The study area, the Sperrgebiet, comprises the majority of Namibia's portion of the succulent karoo biome which is the south-west corner of the country. This is an arid area that has been off limits to public access, farming and tourism for nearly a century due to restrictions imposed by the diamond industry. Methods: Based on existing distribution records, areas of high concentrations of endemic plants were identified using numbers of endemics and weighted endemics according to area of occupancy. The resolution of the available data was quarter degree squares (15-min intervals of latitude and longitude grids). Results: At the scale of this study straight numbers of endemics generated similar results to the endemics weighted according to area of occupancy, which gives sparsely distributed species a higher weighting. Based on the current distribution records, 17.7% (184 species) of the Sperrgebiet's spermatophyte flora is endemic. The 'hotspots of endemism' comprised from north to south: LüderitzKowisberge, Klinghardt Mountains, Aurusberge-Heioab, Witpütz, Skorpion and Obib-Schakalsberge. Taking also areas into account that stand out because of their high proportion of local endemics, this adds Grillental and the central coastal area from Pomona to Baker's Bay to the areas of importance for plant endemism. Main conclusions: The Sperrgebiet's endemic flora is special in taxonomic composition in that it does not present a subset of the total flora of this area, but shows a remarkably high representation of the families Mesembryanthemaceae and Liliaceae (sensu lato). Compared with other arid areas, the level of endemism in the Sperrgebiet is high, but not compared with the succulent karoo in general or other hotspots in the succulent karoo biome, such as the Richtersveld. The proportion of local endemics (13.5%) is high compared with some endemism hotspots in southern Africa. Hotspots of plant endemism provide an important tool to contribute to conservation planning studies. This study also highlighted the importance of centralized data bases without which these analyses would not have been possible. Further plant collecting is required to fill presently data-deficient areas and studies at a finer spatial resolution taking habitat requirements into account are needed to elucidate some of the factors contributing to plant endemism in this area.