Mangrove Forests: One of the World's Threatened Major Tropical Environments

T mass media and scientific press have widely reported losses of tropical environments, such as felling of rain forests and bleaching of coral reefs. This well-merited attention has created a worldwide constituency that supports conservation and restoration efforts in both of these threatened ecosystems. The remarkable degree of public awareness and support has been manifested in benefit rock concerts at Carnegie Hall and in the designation of ice cream flavors after rain forest products. Mangrove forests are another important tropical environment, but these have received much less publicity. Concern about the magnitude of losses of mangrove forests has been voiced mainly in the specialized literature (Saenger et al. 1983, Spalding et al. 1997). Mangrove trees grow ubiquitously as a relatively narrow fringe between land and sea, between latitudes 25°N and 30°S. They form forests of salt-tolerant species, with complex food webs and ecosystem dynamics (Macnae 1968, Lugo and Snedaker 1974, Tomlinson 1986). Destruction of mangrove forests is occurring globally. Global changes such as an increased sea level may affect mangroves (Ellison 1993, Field 1995), although accretion rates in mangrove forests may be large enough to compensate for the present-day rise in sea level (Field 1995). More important, it is human alterations created by conversion of mangroves to mariculture, agriculture, and urbanization, as well as forestry uses and the effects of warfare, that have led to the remarkable recent losses of mangrove habitats (Saenger et al. 1983, Fortes 1988, Marshall 1994, Primavera 1995, Twilley 1998). New data on the magnitude of mangrove area and changes in it have become more readily available, especially with the advent of satellite imagery and the Internet. Moreover, information about the function of mangrove swamps, their importance in the sustainability of the coastal zone, and the effects of human uses of mangrove forests is growing. Some published regional assessments have viewed anthropogenic threats to mangrove forests with alarm (Ong 1982, Fortes 1988, Ellison and Farnsworth 1996), but reviews at the global scale are dated (Linden and Jernelov 1980, Saenger et al. 1983). We collated and revised published information to review the status of mangrove swamps worldwide. To assess the status of this major coastal environment, we compiled and examined available data to quantify the extent of mangrove forest areas in different parts of the world, the losses of mangrove forest area recorded during recent decades, and the relative contributions by various human activities to these losses. We first assessed current mangrove forest area in tropical countries of the world. It is difficult to judge the quality of these data in the published literature, because in many cases the methods used to obtain them were insufficiently described and the associated uncertainty was not indicated. Much information based on satellite imagery is summarized in the World Mangrove Atlas (Spalding et al. 1997). We compared and