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Natural populations of woody perennials on lead-mining sites in the Mechernich area of the Eifel Mountains were investigated with respect to soil factors determining the degree and type of heavy metal tolerance. Salix caprea L.

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The mat‐forming poikilohydric sedge Afrotrilepis pilosa (Cyperaceae) occurs as the dominant member of characteristic stands on West African inselbergs. The species composition of this community has been examined in the Ivory Coast along a latitudinal gradient from the savanna to the rainforest region. Inselbergs consisting of Precambrian granites and gneisses, are prominent landscape elements characterized by large areas of exposed rock. Monocotyledonous mats are one of the most conspicuous communities of this ecosystem. Floristically, the mats are poor in higher plant species with a total of only 15 species (mostly therophytes) recorded in 110 relevés. Species diversity is likewise low, indicating extremely stressful environmental conditions. A major factor affecting plant colonization is the pronounced short‐term variation in water‐availability, even in the more humid regions in the south of the country. Afrotrilepis pilosa is highly competitive under these conditions, and the dense stands leave only little space for other species to become established. Longevity (attaining an age of several hundred years) and the ability, to spread radially to form almost monospecific stands are further characteristics which render this species a superior competitor. In marked contrast with most other tropical vegetation types, Afrotrilepis mats have therefore to be regarded as an example of a naturally occurring, extremely species‐poor community, in which competitive displacement and the low degree of disturbance prevent higher diversity.

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.