Shrub vegetation on tropical granitic inselbergs in French Guiana

In French Guiana, inselbergs in the form of granite outcrops rise abruptly from the surrounding rain forest. They constitute isolated islands of a special type of vegetation restricted to this peculiar substrate. Shrub granitic vegetation, organized in thickets on open exposed rocks of inselbergs, are described using the Braun-Blanquet method combined with Correspondence Analysis. This phytosociological study revealed only one particular shrub community on each inselberg, including predominantly evergreen and sclerophyllous shrubs, especially microphanerophytes, belonging to the Clusiaceae, Myrtaceae and Bombacaceae. These outcrop communities exhibit species endemic to the Guianas region and also species rare in French Guiana. Affinities with flora of other inselbergs and vegetation types in South America are examined and discussed. Reasons for observed floristic and structural changes in each community are also discussed.