TDA-IME Project Final Report June, 2013 Overall, it has been estimated that global climate change is likely to result in the loss of 10- 20% of mangrove forests worldwide, with some areas likely to lose a much higher proportion of their mangroves than others. Particularly vulnerable regions include East Africa, the Bay of Bengal and the western Pacific (Gilman, et al., 2006; Alongi, 2008). Vulnerability and Resilience of Mangrove Ecosystems Because of their unique position at the interface between land and sea, mangrove ecosystems are vulnerable to changes in atmospheric, hydrological and meteorological conditions, and in particular, to rising sea level. In many cases, there are strong linkages between mangroves and other potentially vulnerable ecosystems such as coral reefs. The latter are more vulnerable than mangroves to rising sea temperature; hence mangroves might be affected indirectly by sea temperature change because of its effect on coral reef ecosystems (e.g. coral bleaching). Conversely, mangrove ecosystems have attributes that can promote resilience to climate change and hence they are regarded as an integral component of ecosystem-based adaptation to climate change for many coastal communities in Asia (Macintosh et al., 2009). Ecosystem resilience can be defined as ”the capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks” (Folke et al., 2004). Essentially, mangroves are a dynamic, rather than a ‘steady-state’ ecosystem, and therefore they are capable of adapting to a variable environment. An ecosystem impacted beyond its capacity for resilience will be replaced by an alternative one: this transition may be gradual or abrupt. Many examples of sudden ecosystem transitions have been described (Folke et al., 2004, Seddon et al., 2011). However among the factors promoting resilience in mangroves are below-ground nutrient reservoirs; high rates of nutrient flux and decomposition, resulting in rapid biotic turnover; complex biotic controls enabling internal reuse of resources; and simple tree architecture allowing rapid reconstruction after damage (Alongi 2008). The root systems of mangrove trees also show a remarkable capacity to grow adaptively to suit local conditions, like tidal level and soil texture. Three broad categories of ecological properties support resilience in various ways: diversity, connectivity, and the capacity to adapt (Bernhardt and Leslie 2013). Diversity Species-rich communities are often more productive, use resources more efficiently, recover more rapidly from disturbance, and deter invasive species (Folke et al., 2004 and Bernhardt and Leslie, 2013). In mangrove communities, for example, when mature trees die through storm damage, or for other reasons, the gap is more or less filled rapidly by a succession of species with differing dispersal and shade-tolerating capacities (Putz and Chan, 1986). The mangrove fauna typically includes a variety of species of ecologically similar sesarmid crabs, for example, that play a key role in energy and nutrient cycling. Functional redundancy implies the capacity of one species to compensate for another following disturbance (Bernhardt and Leslie, 2013), hence the number of similar sesarmid species promotes resilience within a mangrove community. Species diversity is, in general, directly related to habitat area. The logarithmic species-area relationship in mangroves has been shown for mangrove tree species and mangrove fauna (Simberloff and Wilson, 1970; Saenger and Bellan, 1995). The causal nature of the relationship between mangrove area and faunal diversity has also been demonstrated (Simberloff, 1976). Conclusion: a reduction in mangrove area could be expected to reduce biodiversity, and hence resilience to the impacts of climate change. 62
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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