TDA-IME Project Final Report June, 2013 SECTION 3 Major Transboundary Issues and Problems Overview On a global scale, and especially within Indochina, the main threats to mangrove forests have been degradation and conversion, which still continue at an alarming rate, although mangrove rehabilitation efforts are partially compensating for earlier mangrove losses in a number of Asian countries. These two closely related destructive processes result from over exploitation of coastal resources (degradation) and land-use changes for development reasons (conversion), especially to agriculture, aquaculture or urban/industrial use. Alongi (2002) noted that mangrove destruction usually has a positive correlation to human population density, implying that this is the main underlying, or “root cause” of mangrove loss. Mangrove degradation results from a wide array of human exploitation activities: extraction of wood for timber, pole wood and fuelwood, including charcoal production; collection of nontimber products; livestock grazing and fodder collection; fishing activities; and partial cutting for boat access, for constructing jetties and house pilings, and for other structures, such as fishing stakes and aquaculture cages (often made from mangrove wood). While these and other uses of mangrove products are traditional and have occurred for centuries at a subsistence level in many Asian countries (e.g. Chan, 1986; Bandaranayake, 1998), spiraling human population pressures have greatly accelerated the degree of mangrove degradation in recent decades, to the point that other valuable services such as shoreline protection, biodiversity support and long-term carbon storage, have been lost or severely compromised. Mangrove conversion, in contrast, in the form of industrial, commercial and urban infrastructure has removed vast areas of mangrove forest permanently. Coastal roads and sea dykes both destroy mangroves and isolate other areas from their natural hydrological regimes, resulting in gradual death of the trees through desiccation or water-logging. Mangrove conversion to agricultural land, salt pans or aquaculture ponds is still potentially reversible (slow, natural regrowth of mangroves, or assisted restoration or rehabilitation may be possible), but this is often hampered by land ownership issues, even when the land seems to have been ‘abandoned’. Estimates of the global mangrove area suggest a loss of 20 to 30% since 1980 (Spalding et al., 1997; Millennium Assessment, 2005; Van Lieveren, et al., 2012). However, the original global mangrove cover is not known, although Spalding et al. (2010) suggest that it could not have been less than 200,000 km2. Even the most recent areal estimates differ widely, from about 110,000 to above 190,000 km2 (reviewed by Giri et al., 2010). The figures of 150,300 km2 (FAO, 2007), 152,361 (Spalding et al., 2010) and 137,760 km2 (Giri et al., 2010) are close to the average based on all the reported estimates. In conclusion, it is probably safe to assume that about one-third of the world’s mangrove forests have been destroyed since the 1950s (Alongi, 2002; Donato et al., 2011) and that the present total is little more than 150,000 km2. While the historical loss of mangroves is imprecisely known, but clearly has been tens of thousands of square kilometres, the recent annual rates of loss have been easier to quantify. Spalding et al. (2010) suggest that the annual average loss of mangroves decreased from just over 1% in the 1980s, to 0.66% per annum during the five years 2000-2005. While this represents a slowing of the annual rate of loss of mangroves, it is still higher than the overall average rate of forest loss globally (0.6% per annum) over the same period (Hansen et al., 2010). 57
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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