Surviving 370 years of human impact: what remains of tree diversity and structure of the lowland wet forests of oceanic island Mauritius?

Mauritius, a 1,865 km(2) oceanic island within the Madagascar and Indian Ocean islands biodiversity hotspot may be regarded as reflecting what awaits many tropical oceanic islands owing to the extreme levels of transformation resulting from over 370 years of human presence. The island has an urgent need to conserve its surviving remnants of native terrestrial habitats. There, however, exists little published quantitative information like species diversity, stem density and basal area in these habitats and other essential parameters for informing their conservation. We surveyed woody native plants in five of the best preserved lowland wet forests using 75 random plots of 100 m(2) (totalling 0.75 ha). Density, dominance and frequency values were calculated along with species and family importance values for each site. For plants a parts per thousand yen1 cm diameter at breast height, 108 species in 66 genera and 39 families were represented by 6,000 individual plants. This gives a density of 8,000 plants per ha which is very high for a lowland wet tropical forest. Species endemism within the plots was 63 % to Mauritius and 87 % to the Mascarenes. Some 56 % of all woody native species ever recorded from the lowland wet forest of Mauritius was sampled. Extrapolated basal area varied from 31 to 49.1 m(2) per ha. The mean similarity in species between pairs of sites was about 60 %. Mauritian wet forests retain the highest tree diversity in the Mascarenes, and probably among all isolated oceanic islands around the world despite massive habitat destruction, extraction and invasion by alien species. Substantial conservation importance and restoration potential still exist.