Biodiversity and vegetation of small-sized inselbergs in a West African rain forest (Taı, Ivory Coast)

The vegetation of small granitic rock outcrops (geomorphologically small-sized inselbergs) which do not reach the canopy was studied in the Ta? rain forest (southwestern Ivory Coast) under aspects of species diversity and phytogeographical affinities. Rock outcrops form edaphically arid (due to absent or very sparse soil cover) and microclimatologically xeric (i.e. low air humidity, temperature regularly exceeding 50°C) islands with cryptogamic crusts, succulents and poikilohydric vascular plants as characteristic elements of their vegetation which differs totally from the surrounding forest. Altogether sixty-six species of vascular plants out of twenty-nine families occur, the number of species correlates positively with inselberg size. Compared with large inselbergs the microclimatic attributes of small-sized rock outcrops are less pronounced. This is accompanied by a decrease of typical inselberg taxa (i.e. species mainly occurring on inselbergs). Low beta diversity between inselbergs indicates deterministic influences as important regulators of species composition. Annual Poaceae and Cyperaceae are richly represented. It can be hypothesized that inselbergs may represent natural growing sites of widely distributed tropical weeds today. Inselbergs might provide habitat resources for savanna elements in rain forest zones.