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

Abstract

he mass media and scientific press have widely reported losses of tropical environments, such as fellingof rain forests and bleaching of coral reefs.This well-meritedattention has created a worldwide constituency that supportsconservation and restoration efforts in both of these threat-ened ecosystems. The remarkable degree of public aware-ness and support has been manifested in benefit rock concertsat Carnegie Hall and in the designation of ice cream flavorsafter rain forest products. Mangrove forests are another im-portant tropical environment,but these have received muchless publicity.Concern about the magnitude of losses of man-grove forests has been voiced mainly in the specialized liter-ature (Saenger et al. 1983, Spalding et al. 1997).Mangrove trees grow ubiquitously as a relatively narrowfringe between land and sea, between latitudes 25°N and30°S.They form forests of salt-tolerant species,with complexfood webs and ecosystem dynamics (Macnae 1968,Lugo andSnedaker 1974, Tomlinson 1986).Destruction of mangrove forests is occurring globally.Global changes such as an increased sea level may affect man-groves (Ellison 1993,Field 1995),although accretion rates inmangrove forests may be large enough to compensate for thepresent-day rise in sea level (Field 1995).More important,itis human alterations created by conversion of mangroves tomariculture,agriculture,and urbanization,as well as forestryuses and the effects of warfare, that have led to the remark-able 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 changesin it have become more readily available, especially with theadvent of satellite imagery and the Internet. Moreover, in-formation about the function of mangrove swamps, theirimportance in the sustainability of the coastal zone, and theeffects of human uses of mangrove forests is growing. Somepublished regional assessments have viewed anthropogenicthreats to mangrove forests with alarm (Ong 1982,Fortes 1988,Ellison and Farnsworth 1996),but reviews at the global scaleare dated (Linden and Jernelov 1980, Saenger et al. 1983).We collated and revised published information to reviewthe status of mangrove swamps worldwide.To assess the sta-tus of this major coastal environment, we compiled and ex-amined available data to quantify the extent of mangroveforest areas in different parts of the world,the losses of man-grove forest area recorded during recent decades, and therelative contributions by various human activities to theselosses.We first assessed current mangrove forest area in tropicalcountries of the world.It is difficult to judge the quality of thesedata in the published literature, because in many cases themethods used to obtain them were insufficiently described andthe associated uncertainty was not indicated. Much infor-mation based on satellite imagery is summarized in the