Landscapes Forest and Global Change - ESA - Escola Superior ...

E. Kouhgardi et al. 2010. Values of mangroves and its interaction with marine ecosystem
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mangrove forests and the fishery sector suggested that for every hectare of forest cleared;
nearby coastal fisheries lose some 480 kg of fish per year (MacKinnon and MacKinnon, 1986).
Mangrove ecosystems are also used for aquaculture, both as open-water estuarine mariculture
(e.g. oysters and mussels) and as pond culture (mainly for shrimps).
Because of its high economic return, shrimp farming has been promoted to boost the national
economy and alleviate poverty in several countries. This activity is often an answer to the
financial constraints on many farmers and local communities and represents a source of
employment. However, if unsustainably planned and managed, it can lead to uncontrolled
deforestation and to pollution of coastal waters, damaged or totally destroyed coastal
ecosystems and the loss of the services and benefits provided by mangroves. A series of
international principles for responsible shrimp farming have been prepared (FAO/Network of
Aquaculture Centers in Asia-Pacific/UNEP/ World Bank/Worldwide Fund for Nature, 2006;
FAO, 1995a), with the main aim of offering guidance on reducing the sector’s environmental
impact while boosting its contribution to poverty alleviation. The principles were welcomed by
many countries (FAO, 2006b)) and will hopefully provide support to the development of more
ecofriendly shrimp production.
The increasing popularity of ecotourism activities also represents a potentially valuable and
sustainable source of income for many local populations, especially where the forests are easy
accessible.
Mangroves also help protect coral reefs, sea-grass beds and shipping lanes by entrapping upland
runoff sediments. This is a key function in preventing and reducing coastal erosion and provides
nearby communities with protection against the effects of wind, waves and water currents. In
the aftermath of the 2004 Indian Ocean tsunami, the protective role of mangroves and other
coastal forests and trees received considerable attention, both in the press and in academic
circles. After more than two years, there are still contrasting views on this issue: eyewitnesses
reported that coastal forests had saved villages from the destruction and lives, while some
analyses asserted that elevation and distance from the coast were more significant determinants
of protection than the forest cover itself.
Even though additional studies are needed to define specific details and limits of this protective
function, the numerous studies and workshops undertaken on this topic over the past couple of
years have brought to light a number of interesting factors. Experts and scientists agree that
thick and dense coastal forest belts, if well designed and managed, have the potential to act as
bioshields for the protection of people and other assets against some tsunamis and other coastal
hazards (i.e. coastal erosion, cyclones, wind and salt spray). However, generalizations – and the
creation of a false sense of protection provided by these bioshields – should be avoided, because
mangroves and other coastal forests are not able to provide effective protection against all levels
of hazards and may not be effective as shields against tsunamis as severe as the one that
occurred in 2004. A full description of the factors to be taken into account with regard to
enhancing the protective functions of mangroves and other coastal forests goes beyond the
scope of this report. Interested readers are referred to FAO (2007) for further information.
2.3 Undervalued resources
Despite the many services and benefits provided by mangroves, these coastal forests have often
been undervalued and viewed as wastelands and unhealthy environments. The high population
pressures frequently present in coastal zones has in some places led to the conversion of
mangrove areas for urban development. In order to increase food security, boost national
economies and improve living standards, many governments encouraged the development of
shrimp and fish farming, agriculture, and salt and rice production in mangrove areas.
Mangroves have also been fragmented and degraded through overexploitation for wood forest
products and pollution. Indirectly, habitats have been lost because of dam construction on rivers,
which often diverts water and modifies the input of sediments, nutrients and freshwater. Even
though dense mangrove forests can be important in coastal protection, natural disasters should
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.