Mangrove vegetation: An evolutionary perspective

The world-wide occurrence of mangrove vegetation and the modem floristic divergence between the Indo-Pacific and the Atlantic mangroves, can only be explained by historical processes, in that the composition of the modem mangrove flora at any one location, while subject to present-day climatic and geographical conditions, is largely relict. Although several interpretations have been offered to relate mangrove distributions to past events, none has been universally accepted. What is explored here, is that there are several historical and modem processes which in combination, have resulted in the present day distribution of mangroves. Evolutionary processes are reviewed from the fossil record and from the data on continental drift. Next, the ecological processes that are selectively acting on the various species and their distributions are examined with particular emphasis on aridity, temperature and latitudinal attentuation of species. Finally, some modem anthropogenic processes (e.g. species introductions, over-exploitation and habitat modification, afforestation) are examined in terms of their effects on mangrove distribution. As an outcome of these various processes, the modem mangrove vegetation is analysed particularly in relation to regions of endemism, vicariance among species, discontinuous distributions, hybridization and divergence. Finally, some speculation is offered in terms of future trends and evolutionary possibilities.