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 × 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 epiphytes 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 Caribbean islands.

Nodulation of Pterocarpus officinalis appears to be widely distributed in the swamp forest of Guadeloupe even under conditions of permanent waterlogging. The large majority of the nodules were found above the water table and as such were located on large aerial buttresses or on root hairs which develop mainly in emerged soil. Further, large trees modify their environment by accumulating litter between the buttresses to the point of ensuring sufficient topographic elevation to keep a volume of soil regularly emerged. Consequently the nodules were concentrated in a small circle (5 m in diameter) around the oldest trees. A few nodules (5%) survived under the water table, provided that healthy root hairs were present, and this kept the rate of nodulation constant over a vertical gradient (0.9 nodule g−1 root DW). The C2H4-evolution rate of P. officinalis, 2.6–5.9 μmol h−1 g−1, appeared to be quite low compared to that of the potted Gliricidia sepium cuttings (19.4 μmol h−1 g−1), but was considerably higher than that of the woody liana Dalbergia monetaria (1.0 μmol h−1 g−1) from the same swamp forest site as P. officinalis. It was concluded that P. officinalis is a N2-fixing tree species under the waterlogged conditions of tropical swamp forests, and was hypothesised that the symbiotic nitrogen fixation on P. officinalis buttresses and root hairs could be considered as an additional adaptation to flooded soil and a contribution to its success in the tropical swamp forests of the Caribbean region.