Mangroves: on the front line of rising sea levels (Cost of Climate Change Post #2)

A United Nations Environment Programme report called Changing Climate and Rising Sea, written with SPREP and WPRFMC in 2006, outlines the economic and ecological significance of mangroves in the Pacific region.   According to the report, “By the year 2100, a reduction in area by as much as 13 percent of the current 524,369 ha of mangroves of the 16 Pacific Island countries and territories where mangroves are indigenous is possible.”

Mangroves are on the front line of damage incurred by rising seas due to climate change, but they have considerable economic value.  Their value has been measured in different ways in different places, but however they are measured, the value of the services they provide is very significant and tends to exceed the cost of preserving them. 

The report expands on this:

“The annual economic values of mangroves, estimated by the cost of the products and services they provide, have been estimated to be USD 200,000 — 900,000 per hectare (Wells et al., 2006).  However, the location and values of the beneficiaries can result in substantial variation in mangrove economic value. For instance, mangroves fronting a highly developed coastline or located near major tourist destinations may have a higher economic value than mangroves in less developed areas with little or no tourism sector development (Wells et al., 2006).  The value of Malaysian mangroves just for storm protection and flood control has been estimated at USD 300,000 per km of coastline, which is based on the cost of replacing the mangroves with rock walls (Ramsar Secretariat, 2001). The  mangroves of Moreton Bay, Australia, were valued in 1988 at USD 4,850 per hectare, based only on the catch of marketable fish (Ramsar Secretariat, 2001).

Mangroves can also be provided with an economic value based on the cost to replace the products and services that they provide, or the cost to restore or enhance mangroves that have been eliminated or degraded. The range of reported costs for mangrove restoration is USD 225 to USD 216,000 per hectare, not including the cost of the land (Lewis, 2005). In Thailand, restoring mangroves is costing USD 946 per hectare while the cost for protecting existing mangroves is only USD 189 per hectare (Ramsar Secretariat, 2001).”

The key message here is that it is worth investing in the protection of existing mangroves but some mangroves are more economically valuable than others.

Of key relevance for Land Resources Division are the following aspects mentioned in the report:

  • Mangroves act as protection of valuable crop land from coastal hazards such as storm surges, coastal erosion, hurricanes, tsunamis and protection of coral reefs from soil and sediment erosion which stem from poor land use.
  • On rising sea levels, “agencies managing coastal land use and coastal ecosystems of Pacific Island countries and territories require assistance to determine trends in relative mean sea level and trends in the frequency and elevations of extreme high water events (Church et al., 2001; Woodworth and Blackman, 2002, 2004; Gilman et al., In Press, 2005b), and assistance to interpret and incorporate this information into land-use planning processes.”  Also, “governments need the institutional capacity to manage a land-use permit or zoning program to ensure coastal earthmoving and development activities are sustainable, including accounting for effects on mangroves, and to plan for any landward mangrove migration.”
  • A final point implied in the report but which I am making explicitly: as sea levels rise, land becomes more scarce and mangroves tend to migrate inland unless natural or artificial barriers stand in their way.  “However small island states have limited capacity to adapt to relative sea level rise, including accommodating landward migration of mangroves and other coastal ecosystems. This is a result of their small land mass, high population densities and growth rates, limited funds, poorly developed infrastructure, and susceptibility to damage from natural disasters (Nurse et al., 2001). It may not be physically or economically feasible for many small island state communities to retreat from a landward migrating mangrove and other coastal habitats, or to establish zoning setbacks from coastal habitats for new development.”  Thus as land gets more scarce, valuable mangroves will compete with other economic projects for land, and the land administration and land use issues around this have to be well managed in order to best adapt to climate change.

*Photo is from the front cover of the report.

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