mangroves-in-the-firing


Just how resilient and protective are mangroves, particularly in the face of tsunamis and global climate change? The way these complex, hardy ecosystems react to major disturbances has been analysed by AIMS mangrove researchers in the paper, "Mangrove forests: resilience, protection from tsunamis and responses to global climate change" in Estuarine, Coastal and Shelf Science.

Mangroves grow fast in a naturally harsh environment and have unique physiology. But are they tough enough for the really big challenges that nature is throwing them at present? There have been few more devastating than the event of 26 December 2004 when a magnitude 9 earthquake produced a tsunami that killed more than 283,000 people in the Indian Ocean region.

In the wake of the Boxing Day 2004 tsunami, it had been suggested in scientific circles that mangroves had saved lives in some areas by absorbing the force of the in-rushing water. Soon after that suggestion had been made in Estuarine, Coastal and Shelf Science, a contradictory paper was submitted suggesting that this was not possible.

An AIMS researcher was called upon to adjudicate by reviewing the existing evidence. It was concluded that mangroves are only protective when certain geographic conditions are in place. For example, villagers living behind a wide expanse of mangroves may receive some protection but those at the funnel end of a river were not protected at all.

The evidence does show that mangroves can "attenuate" (weaken) wave energy, but this was strongly dependent upon forest density, the diameter of the stems and roots, the shape of the forest floor and other physical characteristics.

As for sea level rise caused by climate change, mangroves are meeting the current rate of rise, although that cannot continue indefinitely, and some species are more adept than others at dealing with flooding.

Not enough is known yet about the effect of rises in atmospheric carbon dioxide. Experiments to date are pointing to species-specific responses among mangrove plants, with predictions somewhat confounded by the many variables that affect the process, such as salinity, nutrient availability and water-use efficiency.

While the Inter-governmental Panel on Climate Change (IPCC) is predicting a global loss of coastal wetlands, including mangroves, of around 30 per cent by 2100, AIMS research indicates that it is more likely to be in the order of 10 to 15 per cent.

November 25, 2008