Essential mangrove forest threatened by cryptic ecological degradation

The recent killer tsunami has highlighted once more the importance of coastline protection. In natural conditions, this function is taken up by mangroves, forests thriving at the edge of land and sea that are ecologically and socio-economically important for local people in tropical countries on all continents. Using biology, geography, hydrology, socio-economic interviews, and 18th-century history, an international team led by Dr. Farid Dahdouh-Guebas has demonstrated that in the recent past an increase in human-environment interactions that affect the hydrology of rivers has turned coastal mangrove lagoons into freshwater bodies.

Such elucidation of past ecosystem processes and human-environment interactions is an essential part of the Past Global Changes (PAGES) project of the International Geosphere-Biosphere Programme (IGBP), funded by the U.S. and Swiss National Science Foundations as well as the National Oceanic and Atmospheric Administration (NOAA).

Drawing on diverse data sources, including assessment of contemporary mangrove assemblages in southern Sri Lanka, changing water runoff patterns, and archival material from the Dutch East-India company, the researchers show that over the past few decades contemporary irrigation projects have abused the long-standing Sri Lankan tradition of freshwater management that once sustained robust irrigation-based civilizations. The researchers show that, increasingly, the magnitude of these modern irrigation projects has been such that entire river basins have been diverted to those of other rivers. Whereas these projects certainly develop the ability to grow crops inland, at the same time such practices drastically affect the coastal zone by introducing an excess of fresh water. The consequences range from adverse shifts in the composition of mangrove tree species to disrupted ethnobiological relationships, lagoon fisheries, and many additional functions provided by mangroves.

The authors believe that the worrying aspect of the research is that a degradation of the most vulnerable, most socio-economically important and most aesthetic species is masked by the expansion of less important species. The authors emphasize that such cryptic ecological degradation must be acknowledged by policy and decision makers if mangrove protection is an aim. The research team argues that early detection of such changes should be adopted and is essential for the prevention of further mangrove degradation.

F. Dahdouh-Guebas, S. Hettiarachchi, D. Lo Seen, O. Batelaan, S. Sooriyarachchi, L.P. Jayatissa, and N. Koedam: “Transitions in Ancient Inland Freshwater Resource Management in Sri Lanka Affect Biota and Human Populations in and around Coastal Lagoons”