How mangroves can defend communities in Indonesia from the next tsunami

Jane Madgwick
Fred Pearce

Aceh’s coastal villages in Indonesia were devastated by the 2004 Boxing Day tsunami. The survivors decided to plant mangroves as a buffer against future storms, and so far so good.

Jane Madgwick
Fred Pearce

Indonesian fisher Hajamuddin was at sea the day the 2004 tsunami hit. 

It was the safest place to be. He only felt a mild swell as the wave generated by an earthquake beneath the Indian Ocean headed towards the shore of Aceh, the northernmost province on the Indonesian island of Sumatra. But when he returned to his home port, the coastal village of Gle Jong, he found it obliterated by the giant wave and under three metres of water. A village that had been home to 800 people was an open bay. Just seven residents survived the giant wave that hurtled up the beach that morning. “My family was all gone,” he recounted ten years later. The lucky few were collecting firewood and had time to rush up the steps of the village’s only high point which, with heavy irony, was its cemetery. There, they sheltered among the corpses as their families drowned. 

Gle Jong was one coastal community among hundreds washed away on Boxing Day 2004, when the tsunami battered coasts for thousands of kilometres. An estimated 167,000 people lost their lives in Aceh alone. Another half a million lost their homes. A decade on, the village was on the mend. “People here are still traumatized. The faithful lost their faith,” Hajamuddin admitted. Survivors were still frightened by a glimpse of the ocean or the sound of wind in the trees. But an influx of newcomers such as Hajamuddin’s new wife, and a post-disaster baby boom, had brought the village’s numbers back to 130. They all live in new homes built with international aid and set further back from the coast. 

The recovery was a remarkable story of human resilience. But it was more than that. For the community was doing its best to ensure that, should another tsunami hurtle towards their village, the coastline would be better protected. A few yards inland from the new post-tsunami shore, on land left waterlogged by the killer wave, the survivors have planted 70,000 mangrove trees. “When the floods come again, the mangroves can save us,” said Hajamuddin.

The people of Aceh’s Alue Naga village plant mangrove seedlings to buffer future floods and revive local fisheries · Abdul Hadi Firsawan / Pacific Press / Alamy

Wishful thinking? Maybe not. Research into the tsunami tragedy has shown that a key factor in who lived and who died in coastal communities was whether the natural mangroves that once lined the shore were still there. Often, communities had removed them to make way for prawn ponds, rice paddies, or to make charcoal. But those places that still had mangroves are widely reported to have suffered much less, because the dense foliage and roots dissipated much of the tsunami’s energy.

Such anecdotal conclusions are hard to test in the field, obviously. But they are backed up by some research. One modelling study mimicking a smaller tsunami in Papua New Guinea in 1998, concluded that a 100-metre belt of mangroves reduced the destructive force of the wave by as much as 90 per cent. Another estimated such a belt could reduce wave height by between 13 and 66 per cent. Of course, thousands would have died regardless in Aceh.

Many mangroves were themselves destroyed by the Boxing Day wave. But on the worst-hit western coast of Aceh, field research found that forests in front of villages reduced casualties by an average of 8 per cent. That figure sounds modest, but on the fateful day it could have represented 13,000 lives saved.

Drawing on such findings, the calls to restore the coastal mangroves grew. Initially, to put back the 300 square kilometres of mangroves destroyed or badly damaged by the tsunami. And then to plant more on some of the 600 square kilometres of land permanently swamped by the floodwaters and on land which subsided due to the quake.

Many early projects failed. Most of the mangroves died through poor choice of species and location, or lack of aftercare. Learning the lessons, Wetlands International and Oxfam Novib launched a new initiative. Rather than just paying for villagers to plant trees in a haphazard manner, the Green Coast project offered a deal that emphasized aftercare. In return for giving their labour for planting, groups of villagers were given small loans to help establish enterprises that would revive their communities—everything from opening cafés to buying new fishing nets or setting up goat farms. Crucially, the deal was that if three-quarters of the trees were thriving after two years, then the loans would be written off.

Mangroves are disappearing fast, especially to make room for shrimp and prawn ponds · Pieter van Eijk / Wetlands International

The incentive worked, says Wetlands International’s Indonesian Director, Nyoman Suryadiputra, who masterminded the scheme. Aceh villagers formed groups that planted almost two million seedlings on 1,000 hectares around seventy villages. With better preparation and choice of sites—plus tender loving care from the villagers—more than 80 per cent passed the two-year test, he said. And our visit a decade later suggested that the trees were mostly still thriving. Villagers were proud of them. The dense vegetation was providing visible protection against cyclones, coastal erosion, and any future killer waves. It was also reviving nature. Birds flocked to the cool, new forests. Villagers saw this as a good omen for the revival of their communities.

Some communities were initially reluctant to give up coastal land for planting, particularly when they wanted to restore fish ponds. So, Suryadiputra has worked hard to reconcile the conflicting needs of coastal protection and income generation. Rather than opposing the restoration of fish ponds along the coast, he has instead encouraged villagers to plant mangroves in their ponds and along the dykes between them. 

One village that took up the proposal was Krueng Tunong, a fishing community where rescuers found more than a thousand bodies after the tsunami. A local group planted mangroves around 20 hectares of rehabilitated village ponds. It turned out to be a win-win, they told us. 

“We get more fish [in the ponds] now that there are mangroves,” local leader Wahab said. “They grow faster and in greater numbers than when the ponds were bare. I can see the juveniles hiding in the roots of the mangroves. The roots help them avoid predators. We get more crabs, too.”

In Grong-Grong Capa, on Aceh’s north coast, they formed a planting group of thirty people, one from each household, who planted 16,000 mangroves around the village. “They are getting thicker and thicker now. We get lots of cockles around the roots,” said Nurbaidah, a member of the organizing committee, standing outside her home beside one of the ponds. She picked up a bucket. It contained several hundred large cockles gathered that morning. “Every day we can pick that amount,” she said. Traders from Banda Aceh, the provincial capital, came to her door and paid ten dollars a bucket. But much as she liked the extra income, the main benefit of the mangroves was “to protect our homes from the wind and waves,” she said, gathering her children as the sun set behind her. Nothing was more important than that.

Extreme weather events like the 2004 Boxing Day tsunami are getting worse because of climate change · Water Lands

Mangroves are salt-tolerant trees that grow in shallow tidal waters in tropical regions. They require slow currents, no frost, and plenty of fine silty sediment. Their dense root networks become vital nursery and breeding grounds for marine life, including a large proportion of the world’s coastal fish. The coral of Australia’s Great Barrier Reef might be barren without the nearby mangroves. Mangroves also yield their own harvests of oysters, which cling to their roots, and crabs and cockles living in the surrounding mud. Along with the algae and filter-feeding animals they harbour, mangroves also clean up pollution, especially nutrients from sewage. 

As we have seen, they provide physical as well as ecological services. Mangroves are the best protectors of tropical coastlines. Waves and winds rapidly lose their power as they pass through their dense thickets. They can handle sea-level rise, too. In fact, they thrive on it. The dense roots in a hectare of mangroves can trap up to 20 tonnes of sediment in a year, enough to keep pace with rises up to eight times current rates, says the Australian Institute of Marine Science in Queensland. No sea wall can do that. 

But, just when we could use them, mangroves are disappearing fast—at a rate of some 200 square kilometres a year. They are cut for timber or charcoal, and removed for coastal developments such as ports, industrial zones, oil-palm cultivation and, most of all, ponds for raising fish or prawns. Most Caribbean, Indian, West African, and South Pacific mangroves are long gone. Globally, around 150,000 square kilometres remain, says the Global Mangrove Alliance, a coalition of NGOs. Most are in South-East Asia, where Indonesia has around a quarter, despite losing an estimated 1,150 square kilometres between 2000 and 2012. 

Of the seventy known species of mangroves, more than a dozen are thought to be at risk of extinction. But the good news is that the decline can be reversed.

In places conservation is happening at scale. Indonesia has established the Sembilang National Park on the east coast of Sumatra to safeguard the largest intact mangrove region in South-East Asia.

“We get more fish [in the ponds] now that there are mangroves. They grow faster and in greater numbers than when the ponds were bare.” · Getty Images

Many countries have attempted replanting. A bellwether could be Sri Lanka, a mangrove biodiversity hotspot with twenty-one species. In 2015, the country became the first to declare comprehensive protection of all its surviving mangroves. It recruited 15,000 women in coastal communities to mount patrols to protect the estimated 90 square kilometres of surviving mangroves, and to raise and plant 40 square kilometres of new mangroves in coastal lagoons and abandoned fish ponds. In return, the women get small loans to set up businesses such as bakeries, restaurants, and dressmakers.

Back in Aceh, fisher Mumtadar was waist-deep setting nets in his rented pond. Since he planted mangroves on the banks, the fish have grown bigger and quicker. He harvested 2.4 tonnes a year from his 2 hectares of ponds. Selling at roughly a dollar per kilo, he makes a good living, even after buying larvae and renting the pond, he said. White herons were looking for food in his ponds. But he didn’t object. It showed there were rich pickings. 

The new post-tsunami landscape of Aceh has attracted visitors from around the world to see how this novel combination of fish ponds and mangroves is being achieved. It is certainly not a return to the days when the coastal strip was covered in forests rich with wild boar, monkeys, and even the occasional tiger. But the combination of natural flood protection and ecological nurturing afforded by the mangroves, coupled with the cash-raising power of the ponds, is a compromise the villagers appreciate.

This story is a glimpse of Wetlands International’s Water Lands, a beautiful book about the world's life-giving wetlands. Journalist Fred Pearce and Wetlands International chief executive, Jane Madgwick, will take you on an environmental, cultural and socio-political journey from the peat bogs of Ireland to the marshes of the Brazilian Pantanal. Water Lands will leave you with an understanding of wetlands as in-between and ever-changing worlds that change character with the seasons and are the source of all life. Most importantly, the book sets out a timely call to action for one of the world’s most overlooked ecosystems.

Contributors
Jane Madgwick
CEO, Wetlands International
Fred Pearce
Environment writer
Wetlands International
Wetlands conservation & restoration
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