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Thematic focus: Ecosystem management, Disasters and conflicts, Climate change
Mangrove forest cover fading fast
The uniquely adapted mangrove forests on the marine-terrestrial interface preserve coastline integrity by buffering wave energy from marine processes. The ecosystem services they provide and their support for coastal livelihoods worldwide are worth at least US $1.6 billion a year. Despite their global importance, mangroves are being lost rapidly and action is urgently needed to protect them.
Why is this issue important?
Mangroves are an important bulkhead against climate change: they afford protection for coastal areas from tidal waves and cyclones and are among the most carbon-rich forests in the tropics (Cornforth et al., 2013). In the face of rising sea levels and changing climates, coastal buffering against negative impacts of wave action will become critical and will play an important role in climate change adaptation.
Distributed in the tropical and sub-tropical regions of the world (Figure 1), mangroves provide shoreline protection and an array of ecosystem services. They support nutrient and organic-matter processing, sediment control for other inshore habitats (e.g. seagrass beds and coral reefs), and a source of wood for coastal communities. As a habitat for commercially valuable marine species (Walters et al., 2008), it is estimated that almost 80% of global fish catches are directly or indirectly dependent on mangroves (Ellison et al., 2008; Sullivan, 2005). Thus, the food security for many indigenous coastal communities is closely linked to the health of mangrove ecosystems (Horwitz et al., 2012). As much as 7% of the carbon dioxide reductions required to keep atmospheric concentrations below 450 ppm could be achieved simply by protecting and restoring mangroves, salt marshes and seagrass communities (Nellemann et al., 2009). Mangroves sequester up to 25.5 million tonnes of carbon per year and contribute more than 10% of essential organic carbon to the world’s oceans (Dittmar et al., 2006).
Figure 1: Global mangrove forests distribution – 2000 (Giri et al., 2011). Map redrawn by UNEP/DEWA.
What are the findings?
Mangrove ecosystems, which make up less than 0.4% of the world’s forests (Spalding et al., 2010), are being lost at the rate of about 1% per year (FAO, 2007); in some areas, the rate may be as high as 2 to 8% per year (Miththapala, 2008). From 20% to 35% of the world’s mangrove area has been lost since 1980 (FAO, 2007). The rates of loss are highest in developing countries where mangroves are cleared for coastal development, aquaculture, timber and fuel production (Polidoro et al., 2010). In as few as 100 years, the world’s mangrove forests may become so degraded and reduced in area that they would be considered to have “functionally disappeared” (Duke et al., 2007). Figure 2 shows the areas where mangroves are already threatened in the world.
Figure 2: Proportion of Threatened (Critically Endangered, Endangered, and Vulnerable) Mangrove Species. (Polidoro et al., 2010).
Importance of mangroves
(i) Storm surge protection:
In the Red River Delta in Vietnam, it has been estimated that an earthen sea dyke with a rock face on the open ocean side would require repairs in about five years, whereas the same dyke would last about 50 years if the rock face were replaced by a 100-metre-wide protective mangrove belt (Macintosh and Ashton, 2004). In another project in Vietnam, the cost of planting and protecting mangroves was about US $1.1 million, and the project saved US $7.3 million a year in dyke maintenance. Moreover, during Typhoon Wukong in 2000, the project areas remained unharmed while neighboring provinces suffered major losses in lives, property and livelihoods. The Vietnam Red Cross estimated that some 7,750 families have benefited from mangrove rehabilitation (Reid and Swiderska, 2008).
(ii) Provisioning value:
Figure 3: Factors affecting wave energy in mangroves (McIvor et al., 2012).
Threats to mangroves
(i) Conversion of mangrove forests:
(ii) Global temperature rise:
(iii) Rising sea levels:
(iv) Storms and natural disasters:
Progress in the conservation and restoration of mangroves
Since the 2004 Indian Ocean tsunami, there has been a general increase in the awareness of the importance of mangrove ecosystems; efforts to conserve, protect and restore them can be seen in Bangladesh, India, Indonesia, Myanmar, Seychelles, Sri Lanka, Pakistan, Thailand and Vietnam (Macintosh et al., 2012). The Ministries of Environment and Natural Resources of Guatemala, Honduras and Nicaragua, in collaboration with the UN Environment Programme, have embarked on sustainable mangrove management, raising awareness of the critical role mangroves play in areas that are constantly threatened by the risk of hurricanes and sea level rise (UNEP, 2012).
What are the implications for policy?
As the negative impacts of climate change, including rising sea levels, become more evident, the economic value of coastal wetlands for protection will also increase as the need for their buffering services becomes more critical (Costanza et al., 2008). While market pressures push for mangroves to be cleared for aquaculture and urbanization, coastal land managers must consider not only the value of the services that mangroves provide, but also their potential value in the future (see Box 1).
Mangrove conservation and management
Curbing deforestation may be more effective than reforestation. In the last decade, a study in Thailand found that the cost of restoring mangroves was US $946 per hectare, while the cost for protecting existing mangroves was only US $189 per hectare (Ramsar Secretariat, 2001).
Framework policy and legislation established at national levels, and integrated into a broader spatial framework of coastal zone management, should cross all sectors and involve all stakeholders to prevent piecemeal loss and degradation (Lavieren et al., 2012). For example, countries such as Tanzania and Malaysia have placed all mangroves in forest reserves under state ownership. In some locations in Australia and the United States, local policies of “no net loss” have placed specific limitations on future mangrove clearance. These strategies will be effective in the long term if backed by strong political will, enforcement measures and penalties for noncompliance.
An array of market-oriented strategies have been proposed to curtail the conversion of mangrove areas to other land uses. The fact that mangrove forests are increasingly recognized as a valuable source of revenue should in theory make it easier to entice those who benefit from mangroves to make payments for the ecosystem services that they generate (Lavieren et al., 2012). Furthermore, because mangrove forests store significant amounts of carbon and are threatened by the economic allure of conversion, they could be ideal targets for carbon financing. Such initiatives and investment funds provide exciting new opportunities to better protect natural capital, benefit communities, and utilize cost-effective green technologies to address the challenges of climate change.
Written by: Braedon Cashiona
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