Biodiversity and its dramatic change play an increasingly important role in research and public discussions. Its protection and sustainable use require knowledge about its geographical distribution. One promising approach in this direction is the investigation of indicator groups, since substantial progress in the exploration of approximately 20 Mio species can hardly be expected in the near future. The well-investigated vascular plants, which comprise approximately 300,000 species, are comparatively well suited as indicator groups in terrestrial habitats.
Several examples show the good correlation of their diversity with overall diversity.
In 1996, we published a first world map of the species numbers of vascular plants . The six diversity maxima are all located in the humid tropics and subtropics. Additional centres can be found in Mediterranean-type regions, especially South Africa. It is based on approximately 1,400 records taken from literature and shows the species diversity of vascular plants on a standard area of 10,000 km 2 . Both strategies involve, to a different extent, a reduction of information.