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Mangroves, nature’s shield against typhoons and tsunami

Natures flood defences. Gerald Herbert/AP

Following typhoon Haiyan, the Philippines’ Department for Environment and Natural Resources has earmarked around US$8m to fund efforts to replant much of the affected coastal zone with mangrove forests. Reforesting these coasts with 19m trees, particularly the extensively damaged islands of Leyte and Samar, is a key part of bolstering the first line of defence against future storms. Reports suggest up to 80% of the money is likely to be channelled to residents to engage them in tree planting activities as part of the country’s cash-for-work programme.

Why trees and not, say, concrete? Mangrove forests grow along the coast in fine, salty sediments across the tropics and sub-tropics. Recent research has revealed that mangroves, along with salt marshes and other wetlands, can sequester carbon much more permanently and effectively than terrestrial forests, offering an important means to mitigate global climate change.

But more importantly in this case is their role in coastal protection – something that will grow in importance if storms the magnitude of Haiyan become more frequent with the effects of climate change. The extent to which mangroves reduce the damage caused by typhoons (as well as tsunami) is still debated, but the evidence suggests that mangroves provide an effective natural buffer against storms, flooding, coastal erosion and strong waves.

The value of vanishing mangroves

The global economic value that can be extracted from mangrove forests is estimated by the UNEP at US$1.6 billion per year. Many millions of dollars have been invested in replanting efforts in several of the more than 100 countries with mangroves – as this value has become more widely recognised, and with the effects of storms such as Haiyan. These multi-million dollar investments haven’t always been successful though – it’s not as straightforward as just planting trees.

Replanting damaged areas will depend on the nature of damage caused, the geography, and extent of infrastructure development in the area. It will also depend on how the financial and practical aspects of planting and replanting are addressed, and how local communities are involved. Similar considerations apply in devising ways to protect the remaining mangrove areas, already drastically reduced by more than a third of their global extent. This is largely due to land clearance for agriculture and fish farming, major coastal development, rapid urbanisation, and pollution.

A Vietnamese case study

Having just returned from a study of mangrove forests in Vietnam, we found those living alongside the mangroves use them as a source of food (fish, crabs, clams, worms, octopus, shrimps, jellyfish), either subsisting from them or using their natural resources as a safety net when other food supplies fail. The communities use various formal and informal rules and practices to govern and manage the mangroves.

The formal institutions and governance structures that many of the current restoration and replanting efforts operate through ignore these. They frequently reinforce existing power relations and inequalities, and fail to take into account the importance of community buy-in that can make or break ecological rehabilitation initiatives.

Some groups (often the poor and those with limited livelihood options) are more dependent on certain areas of the mangrove forests, and planting replacement mangroves elsewhere could change or remove how they can access those essential forest benefits. It’s important to develop a clear picture of who, what for, and how the mangroves are used and governed, as a pre-requisite to large-scale planting.

Efforts to plant and replant more mangroves, such as those planned in the Philippines, are laudable. But a clear understanding is needed of the mangrove forests’ role in underpinning the livelihoods of some of the poorest people living along the coast. If the long-term sustainability of any replanting investment is to be assured, then it is vital to understand how the mangroves will be used once the short-term cash to communities for assisting replanting is gone, so that the new forests are not exploited unsustainably.

Finally, detailed consideration needs to be given to the scale and distribution of costs and benefits linked to mangrove restoration and rehabilitation, not just in the Philippines, but globally. Mangroves certainly offer a means to mitigate climate change, conserve biodiversity, and provide a wide range of goods and services as well as protecting coasts against erosion and storm surges. But unless planted and managed carefully, those who depend most upon the mangroves for their survival could lose out.

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