Beni RAHARJO

However, scientists do not come to the same conclusion about the effectiveness of mangrove in tsunami mitigation. First, some scientists ask for more strong scientific evidences. UNEP-WCMC (2006:14) assumes that mangroves and reefs have some defensive function in shore protection but there is no enough scientific evidence to support this argument. The majority of arguments are based on observation and are subjective. However, the facts say the opposite. In Pichavaran and Muthupet of India, areas with intense mangroves have less property’s damage than areas without mangroves (Appropriate Technology 2005:16). Danielsen et al. (2005:643) had similar finding that areas without coastal tree vegetation were noticeably more damaged than areas with this vegetaion.

When a tsunami struck Bangladesh in 1960, nobody died because the coastal area was shielded by healthy mangrove. Subsequently, the mangroves were replaced by shrimp farms. When the next tsunami of the same scale hit Bangladesh in 1991, thousands of people died (Sharma 2005:14). Further information about this study is limited however.

The second uncertainty is the mechanical process. UNEP-WCMC (2006:15) exaggerates that although the capacity of mangrove in buffering seems to be clear, the mechanical processes are complex. The degree to which
scale mangrove can protect the shoreline compared with artificial barriers and other natural features is not well understood. The mangrove is itself destroyed by coastal disasters such as tsunamis. Conversely, other scientists have measure wave forces and modelling fluid dynamics. This computation suggests that tree vegetation can protect the shoreline from tsunamis by decreasing wave?s power and its amplitude. That analytical model shows 30 trees per 100 metres square in a 100 metres wide belt can cut down the maximum tsunami stream power by more than 90 percent (Danielsen et al. 2005:643).

Third, the satellite images analysis does not prove correlation between shoreline damage reduction and the existences of mangroves. In some locations mangroves reported as protecting shorelines from tsunamis, were located in the save zone, or were next to deep sea. This makes those areas less vulnerable to serious impact (UNEP-WCMC 2006:17). This criticism could be true because some research does not reveal a complete description surrounding the area of study; but with the same satellite image tool, another scientist comes into another conclusion nevertheless. Kathiresan and Rajendran (2006:1) conclude that based on satellite images, area with coastal tree vegetation were markedly less damaged than areas without.

Another criticism is that mangroves are not the main factor in reducing tsunami impact. UNEP-WCMC (2006:17) reveals that shoreline bathymetry and profile of coastline are possibly the key factors which help form the wave power at any coastline location. Coasts next to deep water are less susceptible to the tsunami force than those adjacent to shallow water. However, this does not make sense because the effectiveness of mangroves should be compared in the same conditions. In the equal profile of the coastline, mangroves existence is definitely better than mangroves absence.

Finally, effectiveness of mangroves in tsunami mitigation has not been tested in real tsunamis. Kathiresan and Rajendran (2006:1) explain that their study was not based on a large tsunami, but rather a small one of 2.8 metres height. Others studies conducted by Anonimous (2006), Appropriate Technology (2005:16-17) Danielsen et al. (2005:643), Dahdouh-Guebas (2006:187-191), and Sharma (2005:14-15) were mainly based on their observations post-tsunami December 26. It is possibly logical that a good early warning system is a better choice for protection against tsunamis in future disasters rather than mangroves (Luntz 2006:10). However, mangroves and early warning systems are not mutually exclusive; therefore, we can use both of them in tsunami mitigation.

Even the affectivity of mangrove to protect people from tsunami is still debated; people should consider benefits from mangroves. They can give more benefits than artificial protection. Appropriate Technology (2006:5) states that mangrove does not only protect the shoreline, but also can be a feeding ground for a lot of species. For example, fish and shrimp are grown in mangroves before moving into the sea. In relation coral reefs, mangroves are also identified to enrich the population of coral reef fish, therefore maintain their biodiversity. In addition, Danielsen et al. (2005:643) mentions that beside the enhancement of fisheries, mangroves can enhance forestry production too. These benefits are certainly not found in artificial coastal protection construction.

Unfortunately, current conditions of mangroves around the world are generally depressing. Shrimp farms and industrialisation are blamed as the main sources of tarnishing the mangroves. Sharma (2005:14) argues that shrimp farms have replaced more than 50 percent of mangroves worldwide. For example aquaculture and industrialisation started in the 1960s in Thailand have resulted in the elimination of more than 65 thousand hectares of mangroves. In Indonesia, Java Island, 70% of mangroves have vanished. In India, its mangrove forest has decreased by more than two-third in the last 30 years (Sharma 2005:14).

Furthermore, costs and benefits of destroying the mangrove should be taken into account. Shrimp industries are now a $9 billion business; but, one enormous loss caused by a tsunami in 11 Asian countries has recorded an unpriced cost greater than the economic benefits that shrimp industries have produced (Sharma 2005:14).

The current tourism industry throughout the Asia-Pacific countries is connected to mangrove destruction. Hotels and tourism facilities have been built in the coastlines along the Bay of Bengal, the Arabian Sea, and the Strait of Malacca in the Indian Ocean, as well as all the South Pacific Ocean. This region is projected to be visited by 229 million tourists (Sharma 2005:14).

The comprehensive view about mangrove degradation is provided by Dahdouh-Guebas (2006:188). The story of mangroves forest in Latin America, Africa, Asia and Oceania is influenced by negative human impacts such as deforestation, replacing mangrove for shrimp farms, reclamations for tourist hotels and facilities, and fragmentation of mangrove populations by urbanization. These made remarkable losses of mangrove forests in some countries. Based on estimation, the mangrove has decreased from 198.090 km2 in 1980 to 148.530 km2 in 2000. This represents a 25 percent loss only in 2 decades. These losses significantly increase the risk of natural disasters such as cyclones and tsunamis.

In summary, mangroves have important functions in tsunami mitigation. They are shields that can reduce the force of waves and decrease their power to a certain extent so that more people can survive tsunamis. Obviously, based on December 26 tsunami observations and analytical models, we can rely on mangroves as future protection from tsunamis. It is certain that we should integrate mangrove belts and other efforts of tsunami mitigation for complete protection. Regrettably, mangroves are now one of the most threatened natural resources. They should be protected and be enhanced not only for ecological and socioeconomic function, but to reduce the impact of future tsunamis.