TDA-IME Project Final Report June, 2013 Relative Sea Level Rise is a function of overall sea level rise, modulated by rising or falling of the land level, and by net sedimentation levels within the mangroves. Overall sea level rise is predicted by the IPCC survey (Solomon et al., 2007). Uplifting or subsidence of the site as a whole may be caused by tectonic action or sediment compaction (as, for example, in the Ganges Delta: Blasco et al.,1996). Assessment of relative sea level rise can involve tidal gauge data or three-dimensional mapping using techniques such as LIDAR (Light Detection and Ranging), with comparison of historical data, or repeated assessments to establish rates of change. Sedimentation rate If this is not sufficient to keep pace with sea level rise, a site is at greater risk of destruction. Sedimentation rate can be measured directly by installing permanent vertical stakes against which net accretion can be measured periodically. Shore topography A shallow slope indicates a given RSLR will affect a greater horizontal area than a steeper one. Shore gradient may be assessed by standard surveying, or more technical methods such as LIDAR. RSLR may result in the upshore/inland migration of mangroves. An indication of whether this process is occurring may be gained by assessment of whether mangrove losses are occurring at the seaward fringe, and expansion at inland fringe, possibly at the expense of other vegetation such as saltmarsh communities. Historical records, such as aerial photographs or satellite imagery, may already be available to assess mangrove landward migration. Local knowledge can also provide valuable information. The establishment and periodic assessment of permanent upshore/downshore transects can be used to monitor any landward shift by mangroves. However, mangrove upshore migration may be limited by either shore topography or the presence of anthropogenic barriers: agriculture, roads, and buildings. These must be taken into account in vulnerability assessments Other aspects of climate change affect mangrove ecosystem function and health more generally (as do non-climate-related impacts). There are numerous established methods of assessing forest coverage, biodiversity, photosynthesis, productivity and other important ecosystem functions. To discern patterns and changes in these, an appropriate selection of sites, fixed sampling areas, transects or quadrats needs to be established, with periodic repeated assessments at standardized times of year. Much of the value of ecosystem assessment methods lies in between-site comparison, plus time sequence analysis, and these approaches are particularly important in assessing ecosystem vulnerability to climate change. Consequently, standardized methods and procedures, applied similarly across space and time, are crucial for monitoring purposes, and they should be applied at country, transboundary and regional scales. Ellison (2012) presents a comprehensive framework for the vulnerability assessment of mangroves, in which standard assessment methods are discussed in detail, key variables of mangrove habitats measured by those methods are systematically categorized, with semiquantitative figures assigned to different levels of impact (an example is shown in Table 18). These figures can then be combined to give an overall assessment of each site’s vulnerability. The appropriateness and applicability of the Ellison scheme has been demonstrated in disparate mangrove sites, in Cameroon, Tanzania and Fiji (Ellison 2012). It also proved to be a valuable approach in assessing the vulnerability of mangrove habitats in the Indochina. Such methods are suggested as a good starting point from which to develop a regionally-agreed framework for assessing the current status and vulnerability of the Indochina mangrove forest ecosystems. 89
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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