BIODIVERSITY AND VEGETATION OF SMALL-SIZED INSELBERGS IN A WEST-AFRICAN RAIN-FOREST (TAI, IVORY-COAST)

The vegetation of small granitic rock outcrops (geomorphologically sma ll-sized inselbergs) which do not reach the canopy was studied in the Tai rain forest (southwestern Ivory Coast) under aspects of species di versity and phytogeographical affinities. Rock outcrops form edaphical ly arid (due to absent or very sparse soil cover) and microclimatologi cally xeric (i.e. low air humidity, temperature regularly exceeding 50 degrees C) islands with cryptogamic crusts, succulents and poikilohyd ric vascular plants as characteristic elements of their vegetation whi ch differs totally from the surrounding forest. Altogether sixty-six s pecies of vascular plants out of twenty-nine families occur, the numbe r of species correlates positively with inselberg size. Compared with large inselbergs the microclimatic attributes of small-sized rock outc rops are less pronounced. This is accompanied by a decrease of typical inselberg taxa (i.e. species mainly occurring on inselbergs). Low bet a diversity between inselbergs indicates deterministic influences as i mportant regulators of species composition. Annual Poaceae and Cyperac eae are richly represented. It call be hypothesized that inselbergs ma y represent natural growing sites of widely distributed tropical weeds today. Inselbergs might provide habitat resources for savanna element s in rain forest zones.