Box 2.2 FRA 2005 thematic study on mangroves

Mangroves are salt-tolerant forest ecosystems commonly found along sheltered coastlines, in deltas and along river banks in the tropics and subtropics. These trees and shrubs have developed morphological adaptations to tidal environments, such as aerial roots, salt excretion glands and, in some species, vivipary of seeds.

A large proportion of coastal populations in tropical regions depend on mangroves for their subsistence, either directly through the extraction of wood and non-wood forest products, such as fuelwood, charcoal, timber, food and medicines, or indirectly through the many aquatic and terrestrial species for which these ecosystems provide nutrients and a habitat. Mangroves serve as spawning grounds and nurseries for a variety of fish and shellfish, playing a significant role in the marine food system. When mangrove forests are destroyed, declines in local fish catches often result. These ecosystems also play an important role in preventing and reducing coastal erosion, providing nearby communities with protection against the effects of wind, waves and water current. This was demonstrated during the 2004 tsunami in Asia – in locations in which extensive areas of mangroves existed, coastal villages suffered less damage. Moreover, these unique coastal forests provide other important services: conservation of biological diversity and – by trapping sediment from upland erosion – protection of coral reefs, sea-grass beds and shipping lanes against siltation.

Despite their many important uses and benefits, high population pressure in coastal areas has frequently led to the conversion of mangrove areas to other uses, including fish and shrimp farming, agriculture, salt or rice production and urban development. Mangroves have also been fragmented and degraded due to overexploitation and pollution. Numerous case studies describe mangrove losses over time, but comprehensive information at the global level is scarce. Despite past attempts to estimate total mangrove area, recent reliable information on status and trends at the global level is limited. The past attempts include: FAO and UNEP, 1981a, b and c; Saenger, Hegerl and Davie, 1983; groombridge, 1992; Clough, 1993; Diop, 1993; fisher and Spalding, 1993; Lacerda, 1993; Spalding, Blasco and field, 1997; and Aizpuru, Achard and Blasco, 2000.

The FRA 2005 thematic study on mangroves was coordinated by FAO and cofunded by ITTO. it provides an overview of the current extent of mangroves, their species composition, uses and threats, and changes in the extent of mangroves over time for the 124 countries or areas in which they exist. The study aims to facilitate access to comprehensive, comparable information that may serve as a tool for policy- and decision-makers and mangrove managers worldwide. The initiative builds on FRA 1980 and on information provided for FRA 2000 and 2005, for which countries were asked to provide information on current forest area according to forest types, using their own classification systems. Since mangroves form a distinct and relatively easily defined forest type, most countries with mangroves provided specific information on their extent. An extensive literature search and inputs from national mangrove experts yielded additional information. Where recent national information was lacking, it was updated through interpretation of remote sensing data (an in-kind contribution from the UNEP World Conservation Monitoring Centre – WCMC). Local authorities and national experts played a key role in the process of gathering and reviewing the extensive country-level information collected. regression analyses yielded estimates for 1980, 1990, 2000 and 2005 for each country.

About 15.2 million hectares of mangroves currently exist worldwide, down from 18.8 million hectares in 1980, with the largest extent found in Asia, followed by Africa and South America. The area of mangroves present in each country varies from a few hectares to more than 3 million, with close to half the global area found in just five countries: Indonesia, Australia, Brazil, Nigeria and Mexico. Over the last 25 years, 3.6 million hectares of mangroves (or about 20 percent of the total extent found in 1980) have disappeared worldwide. Although alarming, the rate of net loss of mangroves is showing signs of slowing down. from about 185 000 ha lost annually in the 1980s (-1.03 percent per annum), it dropped to some 105 000 ha/year (-0.67 percent) during the 2000–2005 period. This reflects an increased awareness of the value of mangrove ecosystems, which has led, in turn, to the preparation of new legislation, better protection and management and, in some countries, to an expansion of mangrove areas through active planting or natural regeneration.

The detailed findings of the thematic study will constitute an important contribution to the revised World atlas of mangroves (www.fao.org/forestry/site/mangrove-atlas). The study report was being completed for release during 2006. further information on the study and the profiles for the 124 countries or areas in which mangroves occur can be found at www.fao.org/forestry/site/mangrove. The country profiles will also be compiled into five regional reports