Mangroves are unique, yet widespread communities of salt-tolerant trees and shrubs that grow in shallow and brackish ocean water in tropical and subtropical climates. They are adapted to oxygen-poor tidal zones, taking sustenance from the sea and fresh water from the land.1
Mangrove trees have always been known for their distinctive root systems, which rise in lattices above the ground and water, but lately their fame has been growing growing – not for how they look, but for what they do. Mangroves are one of the top three carbon-capturing ecosystems on Earth, sequestering many times more CO2 than most comparable biomes, including seagrass meadows and dry jungle.2 What’s more, degraded and destroyed mangroves can be regenerated and restored to full capacity in a markedly short period of time.3
These attributes mean they could very well play a major role in combating climate change – if we treat them right!
According to CIFOR’s principal scientist Daniel Murdiyarso, mangroves are “a community of plants that grow in saline water and under a wide tidal range.”
That’s a clear and simple description of a complicated and diverse ecosystem. The term “mangrove” refers not only to the type of tree that thrives in shallow salt water – a tree known for its distinctive above-surface root system – but also to the biome they foster and support. Mangroves are essentially a community of salt-tolerant trees and shrubs that evolved to thrive in shallow, oxygen-poor tidal waters, providing a rich habitat for many other species, and often creating strong barriers against the fury of the ocean.
Mangroves are tropical and subtropical plant communities found in tidal waters, either in river estuaries, near-shore basins, or along shallow coastlines.
Almost a quarter of all mangroves grow around the islands of the archipelagic nation of Indonesia, where they cover 2.9 million hectares of coastline – an area roughly the size of Belgium.4 Half of Indonesia’s mangroves (about 10 percent of the world’s stock) are situated on the shores of Papua and West Papua. Much of Indonesia’s remaining stands grow around Borneo and Sumatra.
Mangroves are also common in numerous other near-equatorial countries throughout Asia, Africa, Latin America and the Caribbean.
In Vietnam, they occur mostly in the estuaries of rivers – particularly around the mouth of the Mekong River. They’re also common along the shorelines of most tropical Asian countries. Large concentrations can be found along Myanmar, Thailand and Malaysia’s western coastlines, and in the southern river deltas of Bangladesh and eastern India. Many of the islands of the Philippines are ringed by mangrove stands, as is the large island of New Guinea, which is shared by Indonesia and Papua New Guinea.
In Latin America, most mangroves are found north of the wide mouth of the Amazon River and southeast of the Tocantins River estuary in Brazil. There are also surviving stands in Colombia; in all of the countries of Central America, where they grow on both the Pacific and Caribbean coastlines; and around the islands of the Caribbean itself. Mexico maintains extensive mangrove forests on and near the Yucatán Peninsula, and in scattered locations along the country’s west coast.
Africa’s mangroves are mostly found around the western Gulf of Guinea and the Bight of Benin in Cameroon and Nigeria, but they also extend considerable distances to the northwest and south of these locations. Relatively large stands can also be found along the continent’s Indian Ocean coastline, in Kenya, Tanzania and Mozambique.5
While mangrove areas have often been regarded as useless salty swamps blocking access to good land and the sea, they are in reality supremely important on both local and global scales, and for both people and the environment.
For centuries – perhaps millennia – mangrove stands have helped sustain nearby human populations, providing a sustainable source of food, firewood and building material. Healthy, mature mangroves have also been shown to act as a powerful shield for land and communities from the most harmful effects of cyclones, hurricanes and tsunami. Numerous studies show that the dense networks of roots and branches generated by mangroves are sturdy enough to absorb the first heavy blows of sea surges, dissipating the force and volume of water heading inland.
Other studies have shown that if mangroves are cut down, the areas they once protected often experience far greater devastation than they would otherwise have suffered.
When Hurricane Katrina made landfall on the US state of Louisiana in 2005, levies that had been built to protect the city of New Orleans from sea surges failed to serve their function – largely because the coastline mangroves that would once have absorbed the first brunt of the storm no longer existed. Eighty per cent of the city was flooded and more than 1,000 people were killed.6
A year earlier, an earthquake beneath the Indian Ocean triggered a tsunami that swept into Indonesia’s Aceh province, over much of coastal Thailand and as far away as India and Sri Lanka. Hundreds of thousands of people died. While nothing was able to ward off the force of the full tsunami, those areas still protected by mangroves and other forms of shoreline vegetation were able to withstand the worst effects.7
Mangrove stands not only preserve existing land and coastline, but their growth and spread creates more land and raises the height of the land they inhabit – even to the extent of keeping up with a moderate increase in sea levels.8
On a global scale, mangroves help stabilize the environment by removing and storing more carbon as biomass than most other ecosystems on Earth.
“With their efficient photosynthesis processes, mangroves have a very high rate of biomass production,” explains Daniel Murdiyarso, CIFOR’s principal scientist. “The turnover of leaves and roots is very fast. Large amounts of mangrove litter and fine dead roots are constantly produced and kept in the soil, enriching the below-ground carbon storage.”
The only other biomes that rival mangrove’s capacity to sequester carbon are seagrass meadows, which cover just a tiny fraction of the ocean floor but account for a full 10 percent of all sequestered “blue” carbon9; and peatlands, the sodden vegetation-rich wetlands found in almost every country on Earth. Seagrass meadows store a little less carbon per hectare than mangroves, but they hold onto it for much longer – not just for centuries, but for millennia. Peatland, on the other hand, top the scale for the amount of carbon sequestered per hectare, although mangroves come a close second. All three of these ecosystems are leagues ahead of any other – such as dry prairie, forest or jungle – in both sequestering and retaining carbon from the atmosphere.10
The greatest immediate danger to mangrove stands, without a doubt, comes from saws wielded by human hands. At best, trees are cut down in a sustainable manner to be harvested as firewood or building material. At worst, the mangroves are simply cleared to make way for coastal industrial or residential developments, or for aquacultural and agricultural purposes.11
Fortunately, when mangrove trees are harvested to fuel fires or provide materials for making houses, furniture or artwork, the loss of biomass is sustainable and the ecosystem easily recuperates. Only when the harvesting is conducted on a massive scale and the mangroves are clear-felled does the biome suffer unsustainable harm that results in a massive release of stored carbon, as well as a loss of retention capacity.
While some mangroves are lost to industrial purposes, such as the construction of ports, power plants, and petroleum industry developments, the majority is replaced by pasture, cultivated land, oil palm plantations, or – most notably – aquatic shrimp farms.12
“The [shrimp] farmers need to have their ponds close to seawater to provide favorable conditions for their shrimps,” explains CIFOR’s principal scientist, Daniel Murdiyarso. “One of the quickest ways is clearing mangroves, which are often seen as useless.”
Warfare has also taken a toll on the world’s mangroves – or, more specifically, on Vietnam’s. During the 1960s and early 1970s, American forces used a herbicide and defoliant called Agent Orange to destroy huge swathes of vegetation in the country for military purposes, destroying much of the country’s mangroves in the process.13
These human activities have led to a precipitous and accelerating decline in mangrove ecosystems. Half of the mangroves that existed around the world in 1977 had disappeared within 30 years. In Indonesia alone, an average of 50,000 hectares of mangroves were cleared every year between 1985 and 2000, representing a full 40 percent of the country’s stands.
Overall, the region encompassing North and Central America and the Caribbean has consistently shown the highest rate of mangrove loss when compared to other areas on Earth. In the 20 years ending in 2016, more than seven percent of the region’s mangrove cover (amounting to 1,630 km2) disappeared. Southeast Asia came second in terms of loss rate, at almost six percent, although the region lost a larger area – 2,729 km2. These two regions, as well as the Middle East, exceed the global loss rate of 4.26 per cent, but most other areas are not far behind. Only one region, East Asia, displayed a net gain of 0.55 percent, but it;s worth noting that this area is has only 159 km2 of recorded mangrove forest in total.14
More alarming, however, is the fact that an anticipated rapid rise in sea levels caused by atmospheric warming also threatens the world’s mangroves in their entirety.15 If the waters rise too fast and too high, they will drown most of the planet’s mangrove stands, which will not have time to regenerate naturally by spreading to shallower waters. Scientists calculate that if sea levels rise moderately – that is, 28 to 61 centimeters by the year 2100 – some mangroves would likely survive and propagate. However, if the waters rise more than this – such as between 53 and 98 cm – all fringe mangroves facing the open sea could be gone by 2055, while semi-inland basin mangroves may last until just 2070.
In the short term, the loss of mangroves leaves human populations at the mercy of extreme weather and hydrological events. The winds of hurricanes and cyclones – which are both becoming more violent because of rising atmospheric temperatures – and tsunami triggered by any number of causes, will no longer be restrained by mangrove buffers, and this will cause incalculable loss of life and destruction of communities and ecosystems. For example, researchers estimate that many of the more-than-130,000 people killed in Myanmar by Cyclone Nargis in 2008 could have been saved if the coastal mangroves in that location had not already been cleared.16
In the longer term, clearing mangrove forests releases an enormous amount of stored carbon, in addition to eliminating a mechanism for sequestering more CO2. Researchers estimate that existing Indonesian mangroves still store 3.14 billion tons of carbon in their biomass and underlying soil, and that the country’s ongoing mangrove clearance releases 190 million tons of carbon into the atmosphere every year – the same amount that would be emitted if every car in Indonesia drove around the world twice.17
Globally, mangroves store about 10 billion tons of carbon, which means our environment would take a huge blow if it was all released at the rate it’s occurring in Indonesia. Fortunately, this is not yet the case anywhere except in the Dominican Republic, which was estimated to have more than 21,000 hectares of mangroves in 1998 (a paltry sum compared to Indonesia’s almost 3.5 million a decade earlier).
National governments have had difficulty fitting mangroves into their policy agendas because of the nature of the ecosystem: neither terrestrial nor maritime, but with attributes of both. As it happens, Indonesia is one of several countries that have designated mangroves to be largely, but not entirely, the responsibility of their ministries of forestry.18 However, since mangroves do not lend themselves to large-scale industrial timber harvesting, they do not get serious attention from those ministries, which are usually more focused on exploitation than preservation. In addition, confusion is created because other aspects of Indonesia and other countries’ ‘blue carbon’ policies are under the jurisdiction of a myriad of competing ministries, including maritime affairs, fisheries, tourism, the environment, finance and even defense.
“In Indonesia, there is a lack of national guidelines on how to conserve and restore mangroves. The only regulation [Presidential Regulation No. 73/2012] on the national mangrove ecosystem management strategy is insufficient because it is merely coordinative. Within the regulation, it specifies who should do what but it doesn’t say anything about how,” CIFOR’s principal scientist Daniel Murdiyarso said at a 2017 event entitled ‘Mangrove ecosystems in Indonesia: A strategic resource for local sustainable economy and adaptation to climate change’, which was held to mark World Wetlands Day.In Tanzania’s Rufiji River delta, the central government has made mangroves state property, with the intention of using the law to protect them.19 Unfortunately, the government’s resources have proven inadequate for resisting many of the ways the country’s mangroves are threatened. Local people who plunder the stands for wood and other resources, and raze them to use the land and waters for other economic purposes, have overwhelmed the government’s efforts, which consist mainly of conservation officers burning temporary huts and rice farms. The efforts are not working, according to researchers.
“The threats are increasing and the government alone cannot deal with all these threats,” said CIFOR scientist Baruani Mshale in 2017. “People will always come up with creative ways to access and use the mangroves, regardless of how much protection the government imposes.”
The solution, according to Mshale and others in many other countries, is not to impose conservation from the top down, but to initiate it from the bottom up. In Tanzania, the government has tried to work with farmers rather than fighting with them, but not all of its methods have been successful. Allowing farmers to cultivate rice, on the condition that they allow the mangroves to recover, failed because it did not guarantee them any security; and paying people to replant mangroves has faltered over perceptions that the organizers were favoring certain groups, and because the program did not confer any sense of ownership or control over the forest to the local people. The most promising scheme is one in which the Tanzanian government has retained titular ownership over the mangroves, but transferred many decision-making powers to local people – especially women, who generally turn out to be those who do the most work and take the most interest in its success.
Locally-based solutions are also proving to be most effective in Vietnam, where local people – having lost their mangroves to warfare four or five decades ago and to other causes in the following years – most appreciate the ecosystem’s importance to their lives and their environment. They understand how mangroves contribute to the local economy and provide protection against extreme weather events. Since 2000, the Vietnamese government has invested in programs designed to restore mangroves, and by 2017 had achieved a net annual increase of 554 hectares. While in almost every case the projects have relied on international funding and national coordination, the most vital component so far has been a high level of engagement by local communities and civil society organizations in managing limited areas of mangroves. Generally, provincial efforts are under the management of specific groups that organize people and distribute funds. For example, in Thai Binh Province, a forest protection group manages 2.5 hectares of lagoon mangroves around Hung Long Nam village, both allowing the development of shrimp farms while enforcing the preservation of existing tree stands.20
In Mexico, success has been achieved on the Yucatan Peninsula where the Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV-IPN) conducted a test project on 53 hectares of dry land, converting it in a span of three years into a flourishing mangrove biosystem. The habitat has, so to speak, taken on a life of its own, providing a home to many endemic species of plants and animals, including crocodiles.
Claudia Teutli, a researcher at the National Autonomous University of Mexico, has outlined four lessons for restoring and managing lost mangroves21:
Reestablishing an abundant supply of water is often enough to allow natural regeneration.
The variety of mangrove that originally grew in a degraded area will have the best chance to survive when reintroduced.
A mangrove monoculture will probably die out and, instead, the species needs the support of a varied ecosystem to thrive.
Restoration work is best left to the professional.
In Southeast Asia, on the other hand, a broader approach is being proposed involving, in part, proposals that mangrove stands should be incorporated into marine protected areas (MPAs), thus ascribing them the same level of importance as reefs and fisheries. Proponents also argue that co-management schemes should be established in larger arenas, not just at local community levels, and that public-private partnerships should become more prominent.22
Payments for ecosystem services, which involve paying farmers and other landholders incentives to use the terrain in environmentally friendly ways, are also considered promising for helping to restore and maintain mangroves, especially as such programs can be implemented on both small and large scales.
Money, while generally scarce, can sometimes come from unexpected sources. Take, for example, the actions of former United States President George W. Bush. While in office in 1992, he publicly opposed his country’s participation in a proposed convention on biodiversity during the Rio Earth Summit, but privately he seemed to have a different view on the subject. After he left office, he fulfilled a quiet promise he made to Indonesia’s environment minister at the summit, by donating US$16.5 million to the country on the condition it be used to support the archipelago’s biodiversity.23
At the time, the importance of mangroves and other forms of ‘blue carbon’ was not well or widely recognized, but the money was nevertheless put to good use in founding the Indonesian Biodiversity Foundation, which has worked in Sumatra, Kalimantan, Java and elsewhere to rehabilitate and preserve, dry forest, coral reefs and mangroves, among other ecosystems.
While Bush’s $16.5 million was obviously a substantial amount of money, it is still only a fraction of what is actually needed to deal with the gargantuan problem of environmental degradation, of which mangrove destruction is only one small part. However, investments specifically directed to restoring and preserving mangroves can go a long way toward addressing broader issues, and many governments, international agencies and other organizations have begun to realize this.
The different types of financing available featured strongly in discussions at the Blue Carbon Summit in Jakarta in 2018 – as well as the different types of funders, such as trust funds, development banks and other financial institutions. Unfortunately, in Indonesia and elsewhere, funding for projects related to mangroves is rarely available from domestic banks, which lack appreciation of the economic value of the ecosystem and knowledge of coastal management issues. Banks also frequently lend money to enterprises whose activities result in increased coastal degradation. That means environmental projects must be designed to be more ‘bankable’ – that is, they must become entities that banks can understand and fund easily, as well as enterprises with minimal risks that financial institutions and governments can trust.
Mangrove restoration and preservation projects can be funded through a number of low-risk mechanisms, including grants; equity and bond instruments; first loss/risk sharing instruments; employing results-based payments; guarantee instruments; and environmental funds. Funders must be provided with robust and transparent monitoring, reporting and verification, and be made aware of the benefits that would accrue to both them and other stakeholders.
Carbon dynamics and land use carbon footprints in mangrove-converted aquaculture: The case of the Mahakam Delta, Indonesia, V.B. Arifanti, J.B. Kauffman, et al, Forest Ecology and Management 432, 2019, Link: https://www.cifor.org/knowledge/publication/7031/