The Indonesian island of Java has lost 70 percent of the mangroves that once protected its coast from erosion and flooding. Now villagers are using natural wooden barriers to try to restore the mangrove forests and save their lands and homes from being washed away.

To reach Timbulsloko, a village on the north coast of the Indonesian island of Java, we drove for 3 miles along a narrow causeway. All the way, there were lines of houses strung out on either side of the road. But behind them, rather than fields, there was only water, punctuated by half-submerged fences and the remnants of dykes. Something, it was clear, had gone badly wrong here. Two decades before, this had been all land; but since then, the ocean had steadily invaded. Richer residents along the road were rebuilding their houses on new, higher foundations to keep above the rising tides. Other houses were inundated, abandoned, or marooned on tiny islands that could only be reached by rickety walkways. The village cemetery was being washed away – locals said lapping waters occasionally floated decomposing bodies into their living rooms. At the far end of the causeway, in the meeting hall, village leaders discussed the plight of their community and remembered the old days, before the water came. The village of 3,500 people had been on a prosperous, rice-growing river delta, famous for its fertile soils and protected from the ocean by a wide belt of mangroves. “I grew up in the 1960s when the sea was more than a mile away,” said Slamet, a fisherman. “Then the flooding began.” Beside him, community activist Mat Sairi admitted that the village had made mistakes back then. Like almost every other coastal community in the area, they had wanted to make money by raising prawns and milkfish. So they converted their rice fields into ponds and began cutting down the mangroves along the shore to make more.

“Before, we had a good life with rice and fish,” a villager says. “Now we only have a memory of agricultural land.”

“Our parents warned us that we should protect the mangroves,” he remembered. “They said the mangroves provided many benefits, like the oysters, crabs, and fish among their roots, as well as protection of the coastline. But our people wanted to make money and feed their families.” With the protective mangroves mostly gone, the sea began to wash away the dykes that surrounded the ponds. By 2013, it had penetrated inland for about a mile. The village has lost 25 rows of fish ponds, Sairi said. Now the waters lapped at their houses along the raised causeway. Other nearby villages had been entirely washed away. They feared they might be next. But they had a plan that they believed would save them, by encouraging nature to restore the mangroves. Indonesia, an archipelago of about 18,000 islands, has vast areas of low-lying coast. Once the sea was kept at bay by dense thickets of saltwater-tolerant mangroves. Indonesia still has more mangroves than anywhere else, but they are under huge pressure. The country is now the world’s fourth most populous, and Java is its most densely populated island. As its coastal lowlands have become more crowded, Java has lost 70 percent of its mangroves to rice fields, fish ponds, and other economic activities such as ports and industrial areas, opening up the coastline to rapid erosion. Nowhere has suffered more than Timbulsloko and a string of neighboring villages in Demak, a low-lying district on the island’s north shore. At a meeting in Demak late last year, officials told me that more than 7 square miles of the district had been permanently inundated. In places, the coastline has retreated by more than 2 miles. In 2017 alone, more than 500 people lost their homes, and a thousand fish ponds covering 1,250 acres had been swamped. They predict the future loss of another 25 square miles.

In Java's Demak district, 7 square miles of land has been permanently inundated due to the loss of mangrove forests. Courtesy of Wetlands International

My tour of Demak villages revealed the human stories behind this tragedy. Like Timbulsloko, the village of Bedono was strung out along a raised road now surrounded by sea. Its main community building was built on stilts and nicknamed Bedono Island. Mudskippers and crabs scurried in the muck beneath. “Before, we had a good life with rice and fish,” said the young village head, Agus Salim. “Now we only have a memory of agricultural land.” At Wedung, many of their fish ponds were gone. “We’ve lost 500 meters [1,640 feet] to the sea in the last 10 years,” said Maskur, a teacher on the village committee, as our boat headed out into a new bay that was unmarked on any maps. “I bought 10 hectares [25 acres] of ponds here in 2004, but three years later they were swept away,” said his deputy, Nor Khamed. “If God wants it to happen, it will,” he said with a shrug as a call to prayer rang out from the village mosque. But other villagers along the coast were less fatalistic. “We are not leaving,” said Slamet in Timbulsloko. “This is our home and, God willing, we plan to stay.” Timbulsloko is one of several villages that have banded together to restore their coastline. But rather than calling on the authorities to put up concrete seawalls, they hope to get back their lost land in a novel way.

Eight months after the village of Timbulsloko installed the wooden barriers, the eroding shore was starting to rebuild.

We clambered aboard a boat from the end of the causeway to view a series of long permeable brushwood structures that they had erected in shallow waters that were once productive fields. The structures were rather like outsize nets on tennis courts, each more than 550 feet long and rising more than 3 feet above the waves. They were made up of two lines of vertical bamboo poles hammered 6 feet into the sea bed, with the gap between them filled by a mass of horizontal brushwood, held in place by netting. The structures are not intended to keep out the water, which washes through. Instead, their purpose is to slow the waves coming off the Java Sea so that the tiny particles of sediment carried in the water will drop down and collect on the landward side of the structure, says Femke Tonneijck of the Netherlands-based NGO Wetlands International, which introduced the idea as part of a plan to revive mangroves in coastal regions around the world. In essence, they are a tropical version of a traditional Dutch technique for catching sediment in salt marshes along the shores of the North Sea. The hope in Java is that the deposited sediment will provide a stable base where mangrove seeds floating in the water will germinate and grow, she says. The mangroves will collect yet more sediment, and slowly restore the coastline. After that, the brushwood structures will no longer be needed. Timbulsloko was the first village to volunteer to erect these odd-looking structures, said Sairi, chair of the village group set up to build them. Construction had been hard work. Each required the labor of 25 people for four weeks. There had been teething problems. After clams began to eat the original vertical bamboo poles, they substituted PVC pipes filled with concrete. Others repairs were needed after storms.

A natural sea barrier, built using bamboo and brushwood, in the village of Timbulsloko. The structures help catch sediment, allowing mangroves to take root and regrow. Apri Susanto Astra

But the structures were doing their job. When we reached the first, Sairi put a paddle into the water on either side of the barrier to check the depth. Eight months after its installation, the sea bed was already 6 inches higher on the landward side. In places, 2 feet had been added. The eroding shore was starting to rebuild. By late 2018, nine villages in Demak had erected the brushwood barriers, which were catching sediment along almost 10 miles of coastline. If all goes to plan, they will eventually recreate a green belt of mangroves that will restore the entire coastline, protecting communities and creating new wetland habitat for water birds such as egrets, herons, and the endangered milky stork, said Yus Rusila Noor, Wetlands International’s biodiversity specialist. The villagers are not paid to install the structures. Instead, Wetlands International and its collaborators offer them a deal. In return for their labor, they receive field training in coastal management, plus loans totaling more than $300,000 for local sustainable development projects. These projects have included making organic fertilizers to improve the output of their surviving fish ponds, buying small desalination plants to make the delta water drinkable, and setting up small attractions for tourists. Building boardwalks through newly planted mangroves was a project chosen by some villages. One I visited on the riverbank near Wedung had a bamboo mock-up of a miniature Eiffel Tower as an elaborate gateway.

A tourist boardwalk built in a new stand of mangroves in the village of Wedung. Fred Pearce / Yale e360

Under the deals with the villages, if the barriers are kept repaired, the loans are written off. That has largely happened. At the end of 2018, ownership of the structures in several villages was formally transferred to the communities, with local authorities agreeing to fund future repairs.

The structures exemplify an approach that Wetlands International calls “building with nature” – finding ways to use the forces of nature to solve problems such as coastal erosion. They have undoubtedly halted the rapid erosion of the coastline and begin to nudge it towards recovery. But the outstanding question is whether the mangroves will return and ensure the process continues. During my visit, project leaders had their fingers firmly crossed. This month, Apri Susanto Astra of Wetlands International Indonesia provided an update. “Several locations behind the permeable structures have shown indications of natural mangrove growth,” he said. But it is early days yet. “If the natural mangrove growth does not occur, it can be helped by spreading seeds on the new sediment,” he said. Land subsidence caused by groundwater pumping for industries along the coast is a growing concern. It could, some fear, ultimately negate the benefits from the structures. But the Indonesian government is impressed enough with progress so far that it is adopting the “building with nature” approach, designing variants on the permeable structures to protect vulnerable sandy coastlines, riverbanks, coral reefs, and even the country’s capital, Jakarta.

Carbon deposits have been found in mangrove sediments that are as thick as peat bogs and thousands of years old.

What began a decade ago in Timbulsloko in response to a local crisis is rapidly turning into a grand plan to deploy natural solutions to help protect a nation with more coastline than any other. And the ambition is growing. Mangroves are increasingly being seen by environmental groups not just as a means to protect communities from some of the worst effects of climate change, but also as a tool for helping prevent climate change in the first place. Along with other coastal ecosystems such as salt marshes and sea grasses, mangroves offer a fast and efficient means of catching and storing more carbon in natural ecosystems, so keeping it out of the atmosphere. This “blue carbon” outperforms most rainforests. An acre of mangroves will typically take about 2.8 tons of carbon dioxide (CO2) out of the atmosphere every year, according to the UN’s Intergovernmental Panel on Climate Change. In existing mangrove forests globally, that currently adds up to more than 100 million tons of CO2 a year. Moreover, as individual mangroves die, much of their carbon accumulates in waterlogged sediment, rather than rotting and returning to the atmosphere, which is normally the case for terrestrial forests. Carbon deposits have been found in mangrove sediments that are as thick as peat bogs and thousands of years old.

Villagers who help to build and maintain the seawalls are eligible for loans for local sustainable development projects. Courtesy of Wetlands International

Few restoration projects have yet been launched specifically for their carbon-catching, but many current projects are being assessed to determine if they might attract tradeable carbon credits under international climate agreements or help corporations reduce their carbon footprints. These include restoration of mangroves and coastal wetlands at the mouth of the Mississippi River and in the Florida Everglades; returning mangroves to abandoned shrimp ponds in Thailand and India’s Ganges delta; remaking salt marshes along the Dutch coast of the North Sea; and bringing back lost eelgrass in the Virginia Coast Reserve, which The Nature Conservancy calls the “largest seagrass restoration project in the world.” The world’s richest blue-carbon stores are in Indonesia’s mangroves and sea grasses. They still contain an estimated 3.5 billion tons of carbon. Globally, coastal wetland ecosystems currently hold up to 25 billion tons of “blue carbon,” according to an assessment carried out in 2018 by the National Academy of Sciences. As those ecosystems succumb to development, the store is diminishing. But new policies to protect and revive coastal wetlands could turn the tide. Daniel Murdiyarso at the Indonesia-based Center for International Forestry Research says restoring mangroves could simultaneously allow Indonesia to meet its climate targets, build resilience against rising tides, and improve the livelihoods of millions of coastal inhabitants.