VEGETATION OF ROCK OUTCROPS IN GUINEA - GRANITE INSELBERGS, SANDSTONETABLE MOUNTAINS AND FERRICRETES - REMARKS ON SPECIES NUMBERS AND ENDEMISM

A survey of characteristic plant communities and species occurring on granite inselbergs, sandstone outcrops, and ferricretes in Guinea is g iven. Examples of species restricted to these insular biota are Pitcai rnia feliciana (Bromeliaceae) and Microdracoides squamosus (Cyperaceae ). Rock outcrops harbour characteristic habitat types: cryptogamic cru sts on rocks, drainage channels, crevices, rock pools, shallow depress ions, Afrotrilepis pilosa-mats, ephemeral and wet flush vegetation. Sa ndstone outcrops of the Fouta Djalon are rich in species and endemics probably due to combined effects of vertical differentiation, large ar ea, long-term climatic stability and isolation. Granite inselbergs and ferricretes have no local endemics and a lower number of species. Flo ristic homogeneity of granite inselbergs indicates the importance of d eterministic processes for controlling diversity. The vegetation of Gu inean inselbergs was compared with similar localities in other parts o f tropical Africa. Species diversity of inselbergs in Guinean rain for ests is higher than on inselbergs in Ivorian rain forests due to highe r numbers of growing sites (e.g. rocky slopes of mountain ranges) avai lable for typical inselberg species. Principally, species richness of rock outcrops is positively correlated with the existence of otherwise suitable resources. Supposedly the most diverse inselberg vegetation of tropical Africa is found in Tanzania, Malawi, Mozambique, Zambia, Z imbabwe and Angola.