Phytogeography of bryophytes on the Piton de la Fournaise volcano (Réunion Isld., France): preliminary results.

Abstract : Oceanic islands are unique ecosystems in which hypothesis may be tested to explain their biological diversity. Bryophytes are known to be dispersed over long distances by air currents. New lava flows provide virgin substrates on which plant colonization can take place by means of airborne propagules and spores. Thus the role of the long distance dispersal of bryophyte propagules in the formation of community structure can be better understood. Réunion Island (Mascarene archipelago) along with Madagascar and the neighbouring islands is one of the world’s major biodiversity hot spots. It contains a rich flora with a high diversity of habitats along the elevation from sea level to 3070 m. In the eastern part is located the Piton de la Fournaise, a basaltic effusive volcano, that produces regularly, low width flows, flowing out from an open caldera to the sea. Detailed ecological studies along an altitudinal gradient on a 1986 lava flow and a chronosequence of 6 volcanic events (from the year 1700 to 2004) were undertaken. Bryophytes on these sites were collected and identified at the infraspecific level within 23 microhabitats (rocks, organic material and on vegetation) on the different lava flows. The process of colonization, succession, and maintenance of bryophytes on lava flows were studied. About 190 species of bryophytes were recorded on the lava flows. This study examined the phytogeography of the bryophytes on the lava flows. We discuss how this data set and approach can be used to understand the colonization of the island by land plants.