TDA-IME Project Final Report June, 2013 environmental variables “are unlikely to be additive, and their combinational dynamics are not likely to be linear” (Walther, 2010; Montoya and Raffaelli, 2012;) these factors make detailed prediction difficult. 3) The relationship between biodiversity and ecosystem function in mangroves is 66 unclear Climate change affects species differentially. This means that the relative abundance of species, or the actual species present within a particular mangrove habitat, is likely to change. In one recent assessment, eleven of 70 mangrove species were reported to be facing an elevated threat of extinction (Polidoro et al., 2010). Change in species composition is likely to affect ecosystem function, and the goods and services provided. It has been established, for instance, that the density and species mix of mangroves affects seedling survival and recruitment, and the ability of mangroves to trap sediment, and consequent elevation of the soil surface (Huxham et al., 2010). In temperate mesocosm experiments, invertebrate species richness was found to affect the release of nitrogen (as NH4 -) into the water column (Bulling et al., 2010). Lack of clear understanding of how mangrove ecosystems function makes it impossible to make clear predictions, but it seems likely that biodiversity loss would reduce mangrove ecosystem resilience; and, bearing in mind the species-area relationship (see above), it is likely that smaller areas of mangrove would show lower biodiversity, hence lower resilience. 4) The connectivity between separate mangrove habitats is not clearly understood The degree to which physically separate mangrove stands are mutually interdependent is not understood. It has been demonstrated that the number of species of mangrove in one isolated population is directly related to the distance from other mangrove populations (Saenger and Bellan, 1995). A species at the extreme of its range may depend for recruitment on propagules dispersing from more ‘core’ areas with higher reproductive rates. Depending on the species, mangrove propagules can float for up to 100 days before rooting, so their dispersal potential is considerable. Thus, a mangrove area under stress may have a low in situ reproductive rate, but survive because of propagule immigration from more flourishing areas. 5) Mangroves are connected with other ecosystems Mangroves are connected with other ecosystems: coral reefs, the open sea, rivers. Interaction may be by nutrient or energy flow through soluble or particulate matter, or through the movement of fish, invertebrates, birds or mammals. Climate change impact on one ecosystem impacts other ecosystems. A clearer understanding of the connectivity between different ecosystems is essential to making detailed prediction of the effects of climate change on mangrove forest ecosystems. 6) Will the impact of climate change be incremental, or catastrophic? Predicting a linear response by an ecosystem to incremental change in a single environmental parameter is relatively straightforward. However, a linear response cannot be assumed; and, where several parameters change in parallel, where their effects are not additive, or where complex interactions occur, accurate prediction becomes virtually impossible. What is clear, however, is that the various components of climate change will, separately or in conjunction, place mangrove ecosystems under increasing stress. At some point resilience of the ecosystem will be insufficient to resist this stress, a threshold is passed, and progressive deterioration of the ecosystem will lead to its collapse, or an abrupt shift to an alternative more stable state, such as mudflats, saltmarsh or saline blanks. Although some possible ecological indicators of such impending shifts have been proposed, most thresholds in ecosystems have been detected only after they have already been
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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