Daniel Imbert

Floristics and structure of the Pterocarpus officinalis swamp forest in Guadeloupe, Lesser Antilles.

Swamp forest covers c. 2600 ha of coastal wetlands in Guadeloupe. An inventory of all vascular plants was conducted together with a characterization of the main abiotic descriptors within seventeen 10-m x 40-m plots, systematically sampled throughout the forest. Girth at breast height (GBH) was measured for all trees ,-10 cm GBH. Four forest types were discriminated according to pH, clay content and redox potential of the soils. Among the 107 species recorded, lianas and epiphytes were as much represented as tree species (28%). However, no epi- phytes were encountered at the canopy level where Pterocarpus officinalis (Papilionaceae) was the evenly dominant tree. Local hummock-hollow topography was responsible for an aggregated distribution of P. officinalis. This species exhibits several adaptative traits which may explain its dominance over all of the lowland swamp forests subjected to permanent waterlogging in the hurricane-prone Carib- bean islands.

Ouragans et diversité biologique dans les forêts tropicales. L'exemple de la Guadeloupe

Abstract In this work, we consider the role played by hurricanes in the maintenance of high biodiversity, ,and we look at how biodiversity may influence the response of tropical forest ecosystems to hurricane disturbances. After hurricane Hugo struck Guadeloupe in 1989, we started a comparative study on the resistance and the resilience of the rain forest, the semi-deciduous forest and the mangrove forest. It appeared that the resistance of these forests was positively linked to their diversity, which was assessed both through flora richness and structure complexity (resultin from the variety of life forms). Examples of species specific resistance or vulnerability occur in the three forests; however, the higher the ecosystem diversity, the fewer and the weaker they are. Abundant species tend to be less vulnerable than others — at least in the rain forest and in the semi-deciduous forest. Forest recovery operates mainly through pre-existing individuals (surviving trees, coppicing stumps, saplings or seedlings). Pioneer species may slightly and temporarily benefit from large openings, especially in the rain forest. Strong recurrence of hurricanes may lead to the extinction of some rare, vulnerable, short-range disseminating, non pioneer species.