Stefan Porembski

Vegetation of rock outcrops in Guinea: granite inselbergs, sandstone table mountains and ferricretes — remarks on species numbers and endemism

Summary A survey of characteristic plant communities and species occurring on granite inselbergs, sandstone outcrops, and ferricretes in Guinea is given. Examples of species restricted to these insular biota are Pitcairnia feliciana (Bromeliaceae) and rodracoides squamosus (Cyperaceae) . Rock outcrops harbour characteristic habitat types: cryptogamic crusts on rocks, drainage channels, crevices, rock pools, shallow depressions, Afrotrilepis pilosa -mats, ephemeral and wet flush vegetation. Sandstone outcrops of the Fouta Djalon are rich in species and endemics probably due to combined effects of vertical differentiation, large area, long-term climatic stability and isolation. Granite inselbergs and ferricretes have no local endemics and a lower number of species. Floristic homogeneity of granite inselbergs indicates the importance of deterministic processes for controlling diversity. The vegetation of Guinean inselbergs was compared with similar localities in other parts of tropical Africa. Species diversity of inselbergs in Guinean rain forests is higher than on inselbergs in Ivorian rain forests due to higher numbers of growing sites (e.g. rocky slopes of mountain ranges) available 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, Zimbabwe and Angola.

First protozoa-trapping plant found

Some 450 species of insectivorous plants have been discovered since Darwin published his work on the subject in 1875. We report here the first known case of a plant that traps and digests protozoa.

An inverted latitudinal gradient of plant diversity in shallow depressions on Ivorian inselbergs

The vegetation of shallow depressions on Ivorian granite inselbergs was studied along a gradient from the savanna zone in the north to the rainforest zone in the south of the country. Short-term inundation and prolonged drought are typical features of this habitat. In total, 64 taxa belonging to 25 families were recorded, with the Poaceae, Cyperaceae and Fabaceae accounting for the greatest proportion of species. Annuals represent the predominant life form and comprise nearly two thirds of all species recorded. DCA ordination of the sample plots illustrates that diversity decreases from north to south, and is accompanied by a gradual transition in the ambient vegetation from savanna to rainforest. This decrease is in marked contrast with diversity of surrounding vegetation types. In the drier northern area, it appears as if the less favourable environmental conditions prevent a state of community equilibrium being attained in the shallow depressions. This enables weak competitors to co-exist along with more vigorous species, which, in the south of the country, form species-poor stands. Furthermore, the fact that inselbergs in the rainforest zone are more isolated enhances the probability of extinction of less competitive associates.

Notes on the vegetation of inselbergs in Malawi

Summary Flora and vegetation of Malawian inselbergs are briefly described. Habitat types which are known from other parts of Africa also occur here. Inselbergs in Malawi are floristically richer with many succulents and poikilohydric species and harbour more endemics than those in West Africa. Of major importance for the higher species richness is the isolated massif of Mt. Mulanje. Outstanding examples of endemics are the tree-like Velloziaceae Xerophyta splendens and the Orchidaceae Polystachya johnstonii epiphytic on stems of the preceding species. Apart from widespread species (e.g. Cyanotis lanata ) which are shared with West African inselbergs there is a high degree of floristic divergence with vicariant taxa replacing each other, e.g. the mat-forming Cyperaceae Coleochloa setifera as ecological counterpart of the West African Afrotrilepis pilosa . The inselberg flora of Malawi is largely Zambezian with links to Madagascar.

Selenicereus wittii (Cactaceae): An epiphyte adapted to Amazonian Igapó inundation forests

The biology, ecology, and distribution ofSelenicereus (Strophocactus)wittii, one of the least known taxa ofCactaceae, are described. This epiphyte climbs appressed to tree trunks with leaf-like, flattened stems and is found exclusively along the high waterline of black water rivers (Rio Negro, Vaupés, Apaporis) in the Igapó inundation forests of Amazonia. Ecophysiologically,S. wittii is a crassulacean acid metabolism (CAM) plant. It bears white, nocturnal flowers 25 cm in length which emit a fragrance consisting mainly of benzylalcohol, benzyl benzoate, and benzyl salicylate. They exhibit an extreme sphingophilous syndrome as an adaptation to pollination by probably only two species of hawkmoth from the generaAmphimoena andCocytius. The seeds, aberrant for the family, contain air-filled chambers and are water-dispersed. Thus,S. wittii represents the paradoxical life form of an hydrochorous epiphytic cactus which withstands periodical inundation.

Flora and vegetational aspects of miniature dunes in a sand-depleted Haloxylon salicornicum community in the Kuwait desert

Summary Micro-nebkas are miniature dunes found around the base of dwarf shrubs in deserts and semi-deserts, and which represent distinct habitat patches. Their formation is due to the accumulation of wind-blown sand, particularly on the leeward side of shrubs. The present study provides a first account of the flora and vegetational aspects of such dunes associated with the chenopod Haloxylon salicornicum in a sand-depleted area of Kuwait. Therophytes account for by far the largest proportion (88%) of the 51 species found on the 31 micro-nebkas investigated. Species number on individual mounds is positively correlated with nebka size, not however, with total cover of the accompanying vegetation (i.e. without Haloxylon ). Species with both Saharo-Arabian and Irano-Turanian phytogeographical affinities predominate. At the sand-depleted study site, a distinct pattern was found with respect to vegetation development and species composition on the micro-nebkas. Very striking is the fact that the leeward side of these dunes offers the most favourable growth conditions for the majority of species, as indicated by the dense vegetation cover and more vigorous growth of the individual component species. The importance of micro-nebkas in sand-depleted communities as possible “safe sites” and also in alleviating further desertification processes is briefly discussed.