A large body of evidence indicates that global environmental change is altering species composition, and in turn modifying the pattern of functional trait distributions across tropical and temperate terrestrial forests. However, surprisingly little is known about the patterns of long-term changes in species and functional composition in coastal mangrove forests, which is the reservoir of world’s blue carbon and these forests are threatened globally, owing to climate change, sea level rise and anthropogenic land use changes. Using 110 inventory plots data for the period of 1986 – 2014, together with trait data (wood density, maximum tree height, plant successional stage, salinity tolerance, plant use value), here we examine the patterns of changes in taxonomic and functional composition of Sundarbans mangrove forest, which is the largest single tract of mangrove forest in the world.
Results/Conclusions
Our results indicate major shifts in taxonomic and functional composition of the Sundarbans mangrove forest over the last two decades. Notably, the relative abundance of a salt and disturbance tolerant mid-seral species, Excoecaria agallocha, has increased significantly, while the relative abundance of a relatively less salt and disturbance tolerant climax species, Heritiera fomes has decreased significantly. This is because sea level and salinity in this forest have raised significantly over the last two decades. As a result, the dominance of the forest has changed from Heritiera fomes to Excoecaria agallocha. Accordingly, functional composition of the forest has also changed markedly: species with low wood density and low stature (based on tree height) have taken over the place of species with high wood density and high stature. Moreover, our community weighted mean analyses indicate that the proportions of plots dominated by species with high use value have decreased significantly; that is, the forest’s quality has been degraded. Taken together, coastal mangrove forest may experience remarkable changes in taxonomic and functional properties under the changing coastal environment. Maintaining compositional integrity is thus critical for forest conservation and management under the changing coastal environment.