FloristicDiversity of African and South American Inselbergs: a Comparative View

Porembski Stefan

UniversitätRostock, Institut für Biodiversitätsforschung, Allgemeine undSpezielle Botanik, Rostock, Germany

Inselbergs consist of Precambrian rocksand form ancient (often > 50 million years), stable landscape elements thatare widespread on old crystalline shields. Characterized by harsh environmentalconditions, their vegetation is clearly different from that of thesurroundings. This gives inselbergs island-like attributes, and beinggeologically uniform they bear a vegetation whose composition and diversity isdetermined by the regional climate, vegetation history and localestablishment/extinction dynamics.

On both tropical and temperateinselbergs, a typical set of physiognomically defined habitats (e.g. ephemeralflush vegetation, monocotyledonous mats, rock pools, shallow depressions)occurs.

Globally c. 3500 angiosperm species growon inselbergs. Certain families are characterized by a particularly highpercentage of inselberg specialists, e.g. Velloziaceae (c. 24% of all specieson inselbergs), Lentibulariaceae (c. 16%) and Xyridaceae (11%).Floristically there are largedifferences in species richness and the number of endemics between separateregions, but there is no clear trend of increasing diversity from temperateregions towards the tropics. On African inselbergs Fabaceae, Scrophulariaceaeand Lentibulariaceae belong to the most species-rich families whereasMelastomataceae, Orchidaceae, Bromeliaceae and Euphorbiaceae are dominant on South Americaninselbergs.

With regard to the species richness ofindividual habitats the ephemeral flush vegetation is top ranking on Africaninselbergs in contrast to South American inselbergs where monocotyledonous matsform the most species-rich habitat. According to preliminary data,inselberg-specific taxa in Africa possess larger distributional areas than inSouth America.