TDA-IME Project Final Report June, 2013 scale construction works and land-based runoff constitute a transboundary challenge to mangrove ecosystem integrity, which needs to be addressed by adopting an ecosystembased management approach, including evaluation of the goods and services provided by mangroves for the benefit of small-scale fishers and other traditional coastal dwellers, and how these can be safeguarded? From an ocean perspective, mangrove ecosystems likewise constitute an international waters transboundary management challenge. Many large mangrove ecosystems extend along coasts between countries. Most importantly, mangrove propagules, fish and crustacean larvae, and other biological materials, are dispersed by coastal currents from one mangrove habitat to another, and to marine habitats, including sea grasses and corals reefs. Thus, it is pertinent to note that transboundary issues involving mangroves are not only regional in scope, because they also relate to current and tidal transportation of genetic material from one mangrove ecosystem to the next ecosystem and further afield, but they also encompass mangrove connectivity to other, non-mangrove ecosystems. Biological and Ecological Characteristics The biology and ecology of mangrove ecosystems has been studied extensively over the past thirty years, and there are now a number of books on this subject (e.g. Tomlinson 1986; Robertson and Alongi, 1992; Saenger 2002; Hogarth, 2007; Giesen et al., 2007; Clough, 2013; Ong and Gong, 2013), including country-specific reviews and guidebooks (e.g. Thailand: Aksornkoae, 1993; Viet Nam: Hong and San, 1993; Philippines: Primavera et al. 2004). The Millennium Ecosystem Assessment determined that drivers of global change, such as land use changes and climate change, are threatening the capacity of natural ecosystems to provide key services (MEA, 2005). Biodiversity is widely regarded to be important in maintaining genetic richness, ecological functioning and the resilience of the ecosystem (Schultze and Mooney, 1993 and Heywood, 1995). The Indo-West Pacific region has the highest diversity of mangrove plant species (Duke, 1992; Duke et al., 1998; Ashton and Macintosh, 2002), as well as a rich mangrove fauna (Reid, 1986; Lee, 1998; Ashton et al., 2003a). Ricklefs and Latham (1993) offer a number of explanations for the high diversity in this region: it was the center of origin of mangrove speciation; or the presence of an adjacent diverse terrestrial flora, and a constant wet humid climate, together with the continuous presence of these factors since the end of the Cretaceous, may have enabled a continued increase in diversity, or prevented species extinction, when conditions were not ideal elsewhere. However, a converse explanation of mangrove evolution has been put forward by Ellison et al. (1999). Whatever the correct explanation, the mangroves of Indochina plus Indonesia (collectively the Indomalay Ecozone) represent important refugia of mangrove biodiversity. Consequently, mangrove conservation and sustainable use management are particularly important in this region (Macintosh and Ashton, 2002). Mangrove Flora A great deal is now known about the general floristic characteristics, ecology, growth and productivity of mangrove forests, although there are still many specific gaps in our understanding of the factors that control species distributions, zonation, forest structure and growth. Some 73 species and hybrids of trees, shrubs and ferns are recognized as true mangroves (Spalding et al., 2010), although a wide range of other plants are also found in association and contribute to the floristic diversity of mangrove systems in Southeast Asia, particularly along more landward mangrove zones (Giesen et al., 2007). In this sense, they are 29
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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