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Supertrees: Meet Indonesia’s carbon guardian

Indonesia’s mangroves are an incredibly effective tool against climate change — but they’re being cut down to grow shrimp and palm oil for you.

In a climate emergency, mangrove trees are truly extraordinary: Their ability to store carbon, under the right conditions, is unmatched by any other tree on Earth.
Ardiles Rante for Vox

TANJUNG BATU, Indonesia — Five scientists are wading quickly from the anchored boat through the shallow, silty sea to the dark green shore of East Kalimantan, kicking up plumes of sand. There’s no small talk about the mud that will soon be caking our pants, the heat (102 degrees Fahrenheit), the humidity (thick), the mosquitoes (swarming), or the possibility of a crocodile appearing.

After two flights from the capital, Jakarta, and several boat rides down a river and across a strait, the scientists waited two days at a musty hotel for their instruments, shipped as cargo, to arrive. Having finally made it to this remote, pristine coastal ecosystem they haven’t visited in a year, the researchers are antsy to collect some data.

But they don’t have much time: The tide is already going out, and only two hours remain to do the field research before they run the risk of getting stuck here in a boat beached in sand.

The team’s laid-back leader, Novi Susetyo Adi, gives out directions and everyone scatters, each with a piece of scientific equipment to probe soil, leaves, air, and trees. He then beckons to me to follow him into a tangle of roots, trunks, and snagged plastic bottles as he lays down special measuring tape to document the plant species along it.

Novi Susetyo Adi, a research scientist at Indonesia’s Ministry of Marine Affairs and Fisheries, lays a transect line to study the carbon stored in mangroves in East Kalimantan.

Adi is one of Indonesia’s top experts in coastal ecosystems: He studies the exquisite interconnections between mangroves, seagrass, and coral reefs. Inside mangroves, he’s tuned into the flurry of interactions between mud, water, gases, trees, and hundreds of other busy organisms. With colleagues at Indonesia’s Ministry of Marine Affairs and Fisheries, where he’s a research scientist, he’s both quantifying and preaching the benefits, or “ecosystem services,” of mangroves. The evidence, he hopes, will underlie new policies and laws that ensure the mangroves don’t disappear.

With an estimated 17,500 islands and 34,000 miles of coastline, Indonesia lays claim to the most extensive mangroves on Earth — some 23 percent of the world’s total. Some of the trees are also among the world’s tallest mangroves, reaching 144 feet.

Map of Indonesia outlining coastal mangroves.
The orange lines show Indonesia’s mangrove areas, which make up 23 percent of all the mangroves on Earth and cover 7.1 million acres, the size of Belgium. (The white dot is Tanjung Batu, East Kalimantan, where we visited the stilt mangrove.)
Amanda Northrop/Vox

The vast majority are on the coasts of Papua, Sumatra, and here on Kalimantan, the Indonesian part of the island of Borneo. While scientists have long known these trees and their ecosystem play a huge role in nurturing fish populations and buffering the coast from storms and tsunamis, they’ve only in the past 10 years realized how consequential they are for climate change — as a tool to stave it off.

In August, I accompanied Adi’s team to this site in East Kalimantan to learn more about how mangroves are removing and storing the carbon humans have put in the atmosphere. It turns out these trees — and particularly the outlandishly tall roots and the dense mud beneath them — are a critical tool in a climate emergency, cleaning up some of the atmospheric mess.

More and more coastal experts recognize this, and are trying to elevate the profile of mangroves as one of the most effective forms of land-based climate mitigation. Mangroves are one of a few key natural systems — wetlands, seagrass, forests, and grasslands — that can remove a lot of CO2 from the atmosphere more cheaply than any of the nascent carbon removal technologies. Preserving mangroves is a lot easier than, for example, turning captured carbon dioxide into basalt rock.

To avoid the catastrophic climate scenarios, we’ll need all of the available natural systems plus the nascent technology, and more of both. Every model used by the Intergovernmental Panel on Climate Change (IPCC) requires us to bury huge quantities of carbon dioxide from the air as so-called negative emissions. And every year, the need for negative emissions grows more urgent, with several warming tipping points on the horizon. As the 2019 Arctic Report Card shows, the more the Arctic thaws, the more carbon it unleashes, and the less time we have to avoid runaway global warming.

So where can we save and plant more of these and other carbon-capturing trees? Land on Earth is increasingly scarce, and the tropical forests that remain are being cleared far too quickly. Tropical deforestation generates 8 percent of total emissions, as carbon stored in the soil and wood is released through cutting and burning. Mangroves in particular are being deforested even faster, according to the Nature Conservancy — with even more severe consequences for the global climate, since an acre of mangrove stores five to 10 times as much carbon as an acre of rainforest.

As Adi and I venture deeper into the forest, he suddenly stops and points ahead: “oil palm trees.” Beyond the mangrove labyrinth, I glimpse a neat row of wide, scaly trunks with spiky, pineapple-like green leaves.

Large-scale palm oil production is one of the biggest drivers of deforestation in Indonesia; tens of millions of acres of primary rainforest, peatlands, and coastal lowlands have been cleared to grow the oil-rich fruit for fuel, food, and household products for consumers around the world. (Take a look at the ingredients in your Trader Joe’s snacks and you might see palm oil — chances are it was not harvested sustainably.) Palm oil was also responsible for most of the fierce fires that burned more than 2,500 square miles in Indonesia this year; some 80 percent of the fires were set to clear land for the crop, officials told the New York Times.

In the past year, this oil palm plantation had encroached on Adi’s pristine research site. Later, we would learn that it was just one of several new ones in the area.

When I ask if this was illegal deforestation (a practice that’s still common in Kalimantan), Adi shrugs. “Local people may have had the right to this land, though they’re supposed to stop [650 feet] landward from the highest water line,” a buffer that had clearly been violated. And while this meant that his study would have to be altered, he is surprisingly calm. “This may actually help us learn more about how palm oil plantations affect mangroves,” he says. Most likely, it would be a disaster. “The mangroves here will probably die if this continues because of the direct palm oil-to-mangrove conversion and the potential impact on ground water systems,” he adds, matter of factly.

an aerial shot of a palm oil refinery in East Kalimantan, Indonesia
A palm oil refinery in East Kalimantan on the island of Borneo. Indonesia has lost 40 percent of its mangroves to palm oil, aquaculture, and pollution.

Visiting the Indonesian coast can bring on a kind of whiplash: One moment you’re dazzled by opulent biodiversity — monkeys and bats flying through the air, manta rays swooping through the crystalline water — the next you’re in an environmental hellscape of acrid smoke and burnt tree stumps.

In East Kalimantan, there is blatant ecological tragedy all around: the sad puddles of abandoned shrimp farms where mangroves used to be, a steady stream of open barges piled high with coal polluting the Berau River, rampant theft of sea turtle eggs from sandy beaches, fertilizer runoff from palm oil plantations clouding the sea, out-of-control fires set by farmers to clear land before planting, overfishing, degraded coral reefs, unmanaged human and plastic waste — the insults to this wonderland seem endless.

As an ecologist, Adi can’t afford to grow despondent about any of it; instead, he is playing a long game of trying to protect the ecosystems in the narrow window before climate change and overfishing cross catastrophic thresholds. And thanks to the efforts of his agency and a range of other scientists and advocates, the government is showing increasing willingness to prioritize conservation and biodiversity protection.

Though they’re not yet well monitored or managed, the government has created several Marine Protected Areas, a kind of oceanic and coastal zoning to regulate use, covering about 50 million acres spread out across the vast Indonesian archipelago. Agencies responsible for monitoring and enforcing environmental laws are also getting more funding and support, Adi said.

2020 will be a decisive year: It’s when Indonesia, the world’s fifth-biggest greenhouse gas emitter, and the rest of the world (except the United States) is expected to submit new “enhanced” commitments to reduce emissions under the Paris climate agreement. It’s an urgent step given that current promises are vague and insufficient; some of the details are being hashed out this week in Madrid, at the UN climate change conference. 2020 is also when Indonesia will begin integrating the recommendations from its new Low Carbon Development Initiative into its 2020-2024 national development plan.

The LCDI lays out a path to cut greenhouse gas emissions nearly 43 percent by 2030, and Adi wants to make sure mangrove protection and restoration play a big part. But the specific challenge facing Indonesia and other countries with large stocks of mangroves is huge: to ramp up environmental law enforcement while also educating and persuading local communities that they’re better off in the long run managing the ecosystem carefully, so it remains intact.

It’s a race against intense local and multinational pressures to extract quick cash from the land. Unless the country can dramatically slow down mangrove destruction, one of Indonesia’s best climate assets will end up only accelerating the emergency.

Mangroves are terrific at storing carbon, but there’s tremendous damage when they’re disturbed

Before we dive deeper into the extraordinary underground superpower of Indonesia’s mangroves, a word about this ecosystem more generally.

There are 80 species of mangrove trees, all of which grow in coastal or riverine soils with little oxygen — a special middle zone between the land and ocean. These trees like salty and brackish waters and can tolerate the salt because their roots have a special system that filters seawater, according to the Global Mangrove Alliance.

After Indonesia, the countries with the largest areas of mangrove forest are Brazil, Australia, Nigeria, and Mexico. In the US, you can find them along the Gulf Coast, from the tip of Florida to Texas. Everglades National Park in Florida, notably, has the largest stand of protected mangrove forest in the Western Hemisphere.

But as an exceptionally large archipelago with close proximity to the equator, Indonesia stands out for the richness and extent of its mangroves and the biodiversity they contain. Here, in the mangrove tree branches, one finds a huge species of bat called the large flying fox and proboscis monkeys, whose males feature bulbous schnozzes. Lurking among and above the roots and the mud, there are crocodiles, crabs, sea stars, sand dollars, hornbill, and kingfisher. In the water lapping at the thicket of roots, young fish, like snapper and grouper, and plankton take refuge from predators. Sea turtles nibble the seagrass that’s often nearby.

In the water lapping at mangrove roots, young fish and plankton take refuge from predators.

Fishermen in this region are well-acquainted with the mangroves’ many perks. One fisherman I met in East Kalimantan told me he often escaped howling winds by hiding in mangroves, and the trees have long been a living shelter for the sea nomads of this region, the Bajau people. The ecosystem also recycles nutrients, cleans up pollution, and protects the coast from storms and floods.

If a mangrove forest is not overexploited, the trees can be a source of timber for building houses and charcoal. Most species grow back entirely within 30 to 50 years, said Meriadec Sillanpaa, a PhD student at the National University of Singapore who studies the mangrove forests of West Papua, Indonesia.

But it’s only now — in the age of climate change — that we’re beginning to understand how mangroves are truly extraordinary: their ability to store carbon, under the right conditions, is unmatched by any other tree on Earth. The rainforests of the Amazon and Congo Basin are critically important carbon sinks, no doubt, but tree for tree, mangroves can beat the pants off them at sequestering carbon from the atmosphere.

Several species of mangrove have the superpower, but let’s take one common to Indonesia, called Rhizophora, the stilt mangrove, as an example. Here’s how it works: First, the tree absorbs carbon dioxide from the atmosphere and, through photosynthesis, grows leaves, branches, roots, and a trunk. Over time, this carbon-rich plant material eventually breaks off. Most of that dead plant material is then trapped in the salty, wet soil beneath the roots.

Graphic showing how the stilt mangrove absorbs carbon dioxide from the atmosphere. Amanda Northrop/Vox

Those roots clutch the organic matter that falls from the trees. “The more complicated root systems in Indonesian mangroves means trees can store more carbon,” Adi said.

In a forest on land, and even in a rainforest, there’s more oxygen in the soil. The organisms that break down plants and release carbon back into the air need oxygen to do their work. But in the wet mud underneath mangrove trees, there’s very little oxygen, so the plant matter can’t decompose and the carbon stored in it can’t return to the atmosphere. Instead of being released, the carbon can accumulate up to 20 feet below the surface, and remain there for millennia. (Seagrass and salt marshes are two other oceanic and coastal ecosystems that can store a lot of carbon; collectively it’s known as “blue carbon.”)

“If you preserve a mangrove, you’re preserving an active carbon sink, because the ecosystem keeps taking in carbon continuously,” Sillanpaa said. “It’s a highly biodiverse, dynamic, resilient ecosystem. If we utilize it sustainably it will be there.”

According to Daniel Murdiyarso, a principal scientist at the Center for International Forestry Research, Indonesia’s 7.2 million acres of mangroves are “globally significant sinks of carbon.” In all, Adi estimates that Indonesia’s mangroves and seagrass together store 2,890 gigatons of carbon, a quantity that, if released, would far overshoot the entire world’s remaining emissions budget to limit warming to 1.5 degrees Celsius.

Conservation International estimates that as much as 1 gigaton of CO2 is currently being released annually from degraded coastal ecosystems worldwide, including mangroves. That’s equivalent to the total annual emissions from cars, buses, aircraft, and boats in the US in 2017.

If you chop down a mangrove tree, the exposed soil beneath becomes a big climate problem. When trees are removed, and the blue carbon beneath is exposed to air, the carbon reacts with oxygen to produce carbon dioxide and methane, two greenhouse gases that contribute to global warming. A Scientific Reports study looking at mangroves in Thailand found that 70 percent of their carbon is lost when mangroves are converted to shrimp ponds. Murdiyarso and colleagues found in research published in Nature Geoscience that mangrove deforestation worldwide generates “as much as around 10% of emissions from deforestation globally, despite accounting for just 0.7% of tropical forest area.”

A stilt mangrove tree in a protected area on  Semama Island in East Kalimantan.
A stilt mangrove tree in a protected area on Semama Island in East Kalimantan.

Humans aren’t just endangering mangroves by cutting them down: Scientists are also increasingly worried about how sea-level rise and more severe hurricanes and typhoons (both linked to climate change) are affecting mangroves, battering them with winds and storm surge. “Mangroves are a very important indicator — they can pick up on changes to sea level because the habitat is critically connected to it, being in the intertidal zone,” said Norman Duke, a senior research scientist at James Cook University in Australia. Though mangroves have a reputation of being incredibly resilient, “shorelines damaged in one event no longer have time to recover ... before the next severe event,” he added.

Scientists are getting better measurements of Indonesia’s blue carbon

If you tag along with climate scientists in the Arctic, you might see them drilling for ice cores. Sediment coring is the coastal climate scientist’s corollary. In just one meter-long core of sediment, scientists can find out how much carbon is in there and how long it has been there. Adi and his colleague Mohammed Sumiran Paputungan at first couldn’t get the device into the thick mud, so they took turns, jumping and pushing on it, like a pogo stick that didn’t bounce.

The scientists also had a new piece of equipment on loan from their Japanese partners to measure the photosynthetic rate of stilt mangrove and other species. “This is super important for figuring out how much carbon is being absorbed from the atmosphere,” Adi told me. They want to know how much carbon is in the biomass above ground, and how much is in the mud below ground.

Another team member was measuring the roots to see how long they grow. The general rule, Adi said, is that the more roots, the more sediment trapped below. “If we know the growth rate of the roots and the sedimentation system we can figure out how much carbon [the ecosystem] can take,” Adi said.

Sea-level rise and more severe hurricanes and typhoons are also endangering mangroves.
Adi pushes a sediment coring device into the mud to collect a sample to measure the carbon underground.
Adi, far left, and his team from the Ministry of Fisheries and Marine Affairs and local universities finish their field work in East Kalimantan.

This work will help generate more precise and nuanced measurements of Indonesia’s blue carbon. For instance, Adi says carbon storage seems to vary quite a bit between mangroves on riverbanks compared to those on the ocean (ocean mangroves have more).

This research will be key as Indonesia updates its inventory of greenhouse gas emissions and removals; the last version didn’t include any of the carbon stored in mangroves or other marine ecosystems. And the inventory is critical for helping the country figure out how to reduce emissions and meet its commitments under the Paris climate agreement.

If the country can account for all the carbon its remaining mangroves are sequestering, it might help incentivize government agencies to shore up protection. Adi says his work will also help the planning ministry add a new marine and fisheries sector to the Low Carbon Development Initiative plan.

But the hardest part is translating the science into policy and action that filters all the way down to the local level in places like East Kalimantan. “We can calculate how much carbon can be absorbed by natural ecosystems with [a mathematical] formula, that’s easy,” Adi laughed. “The hard part is the implementation of this.”

Why it’s so hard to protect mangroves in Indonesia

Over the past three decades, Indonesia has lost 40 percent of its mangroves to aquaculture (shrimp and crab for export, mainly to China and the United States), palm oil (for local use and export to the US and other foreign markets), and pollution. Mostly, it’s happening because of steady population growth, dwindling available land for agriculture, and a dearth of employment opportunities. The World Bank calls Indonesia an “emerging lower middle-income country,” and though it has cut its poverty rate by more than half since 1999, some 26 million Indonesians still live below the poverty line.

“A lot of people are relying on the mangrove ecosystem, in these low-lying coastal areas, with high population density,” Murdiyarso said. “They are quite something in terms of livelihood for people.”

Most people living in Indonesia’s mangrove regions survive as fishermen, but overfishing has depleted the stocks, forcing many who once could count on the ocean to try their hand at aquaculture. “It used to be you could wade into the sea and feel shrimp up to your shins,” a woman in the village of Pisang Pisang told me.

Aerial view of Derawan Island
The mangrove forest on the island of Derawan in East Kalimantan has been almost entirely cleared to make way for hotels, homes, and coconut trees.

In East Kalimantan, I met up with Nono Rachmad Basuki, who runs the Berau office of the Turtle Foundation, an international organization focused on sea turtle conservation in Indonesia and Cape Verde. He said the local government is slowly becoming more interested in protecting mangroves — mainly to ensure the fisheries remain robust and communities in the region remain employed.

His organization is also trying to show the government and local communities that the mangrove ecosystem, if left mostly intact, can provide fruit and dyes for batik cloth. This fall, community members near Pisang Pisang trained by the Turtle Foundation began to sell their first mangrove products.

But Rachmad Basuki is worried that the local government doesn’t have much control over the public lands in the region because they’re managed by different agencies in the central government. And there are few staff members on the ground. In the six years he’s been living in Berau, he’s seen many hundreds of acres of mangroves converted into shrimp and crab farms, often by newcomers who come to East Kalimantan from the island of Sulawesi to seek their fortune.

Though there are now more restrictions on new shrimp farms, he’s worried some shrimp and crab producers will keep expanding their farms into intact mangroves. And he’s concerned the local and provincial governments will continue selling large concessions of rainforest and mangrove to multinational palm oil producers.

As Rachmad Basuki explained, there’s also considerable confusion over who owns various undeveloped parcels of land in Berau. The area is relatively undeveloped, with few roads and lots of waterways, which means it’s possible to grab land illegally and develop it without the authorities finding out for some time.

Then there’s the issue of monitoring: If someone destroys a protected mangrove illegally to build a shrimp farm, does the Ministry of Environment and Forestry have enough rangers on the ground to go after them and pursue legal action? Who’s going to ensure that someone else doesn’t do the same thing right next to it?

“If it’s no one’s land, it has problems. You can jump into it, and abandon it and nobody cares about it,” said Murdiyarso, who says this is an issue in many mangrove areas. It also helps explain why there are half a million acres of abandoned shrimp farms scattered throughout the country. (The government says it wants to rehabilitate them, to restore some of the lost carbon and other ecosystem benefits, though that can take decades.)

Will the Indonesian government — and its international partners — find a way to protect enough mangroves?

A small number of experts have been singing the praises of mangroves as a climate mitigation strategy for a few years now. “If you had a dollar to invest in carbon futures, my strongest advice of all would be to invest in preventing mangrove loss, or even restoration,” wrote Mark Spalding, a senior marine scientist with the Nature Conservancy, in 2013.

The latest numbers make an even better case: A recent report from the Global Commission on Adaptation found that the combined benefits from mangrove preservation and restoration are up to 10 times the costs of replanting them.

But using land to mitigate climate change requires a lot of coordination, law enforcement, and education. As Calum Brown of the Institute of Meteorology and Climate Research – Atmospheric Environmental Research argued in an article for the UK website Carbon Brief, “Most political systems — focusing on particular geographic or policy areas — are poorly suited to handling this complexity.” Still, he says, it is entirely possible to protect tropical forests along with peoples’ livelihoods.

Adi noted that Indonesia now has some examples of sustainable mangrove management, including one project supported by the government and several NGOs in northern Java, where 12 miles of mangroves have been restored by a community of 70,000 people. Another project in northern Sumatra involved the rehabilitation of hundreds of acres of degraded mangroves, and the local community is now able to earn income from them.

Activists and mangrove lovers plant mangrove seedlings in October 2019 on Palu Bay, Central Sulawesi, a coastal area in Indonesia that was damaged by a tsunami in 2018.
Activists and mangrove lovers plant mangrove seedlings in October 2019 on the coast of Palu Bay in Central Sulawesi, which was damaged by a tsunami in 2018.
Basri Marzuki/NurPhoto via Getty Images

While international NGOs have tried to pressure Indonesia from the outside, the efforts of Murdiyarso, Adi, and others on the inside have helped focus the country’s leaders on the opportunities in blue carbon.

International NGOs, like Conservation International (CI) and the Nature Conservancy (TNC), see a shift underway. “Indonesia now has a lot of political will to do something about blue carbon. The government has set up teams in ministries to take all that information outside the blue carbon community,” Jennifer Howard, CI’s marine climate change director, told me.

Adi agrees: “Tsunamis have taken a toll, the casualties have been bad. The government is getting more familiar with all the ways that mangroves are beneficial. Now there are more and more conservation regulations happening.”

Lisa Schindler Murray, an international climate policy advisor at TNC, noted that Indonesia’s revision to its commitment under the Paris agreement in 2020 will also be very revealing. “One thing that we’re looking for as a proxy for how countries are valuing their mangroves, and other natural climate solutions, is in their climate actions plans, or NDCs,” Schindler Murray said. “Being able to have a high level of commitment in those documents is really important.”

Murdiyarso and others, including the Washington, DC-based environmental think tank the World Resources Institute, have been calling for a moratorium on mangrove deforestation to ensure emissions reduction targets are met. Adi agrees one is needed, but he doesn’t want it to be a standalone policy.

“Yes, we need a moratorium, but it is ongoing and it is embedded in existing policies,” he said. “It is part of expanding our marine protected areas. We also have the marine special planning, where we have to reserve like a greenbelt of mangroves. We also have the national strategy for mangrove rehabilitation.” A freeze on large-scale cutting, he said, can fit into all of those policies.

A volunteer examines new mangrove trees on Teluk Palu Beach, Central Sulawesi, Indonesia, on July 26, 2019.
A volunteer examines new mangrove trees on Teluk Palu Beach, Central Sulawesi, Indonesia, on July 26, 2019.
Basri Marzuki/NurPhoto via Getty Images

Carbon trading schemes — where communities that manage carbon-rich ecosystems can be compensated for managing them sustainably — are also emerging as a way to incentivize local communities not to cut them down or sell them. But as there’s no global price on carbon, such projects so far are voluntary, very small, and require the support of international donors.

Adi urges caution here: “When we decide to implement carbon trading we need to be careful because otherwise the local community, which has a very important role in conserving the mangrove, will think it’s like a trade for money.” He’d rather have them appreciate and value all of the mangroves’ benefits — to fisheries, storm protection, filtering nutrients — instead of reducing their worth entirely to carbon banking.

Figuring out how to stop rampant resource exploitation in Indonesia can’t be done without addressing the limited opportunities of local communities. And that’s why Adi’s keen to engage with them.

“It’s so important to raise public awareness that mangroves are a habitat for fish and interesting for tourists,” he said. “We need to work really hard to make local communities understand.” And, when it comes to climate change, “local” actually includes all of us.


Ardiles Rantes is an Indonesian freelance photojournalist and producer who has studied politics, journalism, and photography.

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