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Loss of Mangrove Forests Worldwide Is Slowing – Except in Asia

Loss of Mangrove Forests Worldwide Is Slowing – Except in Asia

Mangrove forest located in Mida Creek, Kenya. Photo: Photo by Timothy K/Unsplash, (CC BY-SA)

The vast tangled mangrove forests that sweep along so many tropical coasts are one of the world’s most biodiverse ecosystems. They also play crucial roles in protecting coastlines from erosion and providing communities with resources from food to firewood, and are one of our most effective carbon sinks.

Yet they continue to be destroyed and degraded. In their Global Forest Resources Assessment (FRA) for 2020, the Food and Agriculture Organization of the United Nations (FAO) estimated the loss of 1.04 million hectares (2.57 million acres) over the last 30 years. However, there is some cause for some optimism. According to figures from the FRA, the rate of global mangrove loss has more than halved over three decades, from 46,700 ha (115,400 acres) of loss per year between 1990 and 2000, to 21,200 ha (52,400 acres) per year between 2010 and 2020.

However, not all regions have experienced a reduction in mangrove deforestation. The FRA found that in Asia, there has been a huge increase in mangrove loss: from 1,030 ha (2,550 acres) per year to 38,200 ha (94,400 acres) over the same 30-year period.

Now conservationists hope that a process called ecological mangrove restoration (EMR), which is proving far more successful at restoring these forests than previous well-intended but often ill-conceived efforts, will help turn the tide once and for all in the battle to save the mangrove.

Vanishing blue forests

There are about 70 species of mangroves, with the greatest biodiversity in Asia, followed by Brazil, Australia, Nigeria and Mexico. They grow from the land toward the sea, and inhabit an intertidal zone where a unique filtration system makes them one of the few plants that can survive in brackish or salty water.

Also read: How Mangroves Protect People From Increasingly Powerful Storms

Because of their proximity to water, mangroves are often called “blue forests.” Their masses of roots extend above and below the water line, helping to slow the movement of water, stabilize coastlines and reduce the impacts of waves and storm surges. They also serve as important nursuries for a vast array of fish, as well as habitat for a range of animals from hippos (Hippopotamus amphibius) and dugongs (Dugong dugon) in Tanzania, to the Atlantic humpback dolphin (Sousa teuszii) in Senegal. In Panama, pygmy sloths (Bradypus pygmaeus) clamber through the canopy, while Bengal tigers (Panthera tigris tigris) patrol the swamps of the Sundarbans in India and Bangladesh. Everywhere, the forests attract huge flocks of birds.

A Bengal tiger surveys its domain in the Sundarbans mangrove. Image by Soumyajit Nandy via WIkimedia Commons (CC 4.0)
A Bengal tiger (Panthera tigris tigris) surveys its domain in the Sundarbans mangrove. Photo: Soumyajit Nandy/ Wikimedia Commons, CC 4.0

Through photosynthesis, mangroves absorb huge amounts of carbon. Research indicates a hectare of mangrove can lock away four times more carbon than the same area of tropical rainforest.

Only seagrass meadows and mudflats are more effective at sequestering carbon, both of which also have fascinating symbiotic relationships with mangroves. While they help to reduce the power of waves crashing into the mangroves, the mangroves reciprocate by  helping to protect these offshore habitats from being smothered by silt and other runoff from the land.

Wetlands International (WI) is one of the key champions of EMR, running projects across Asia and Africa. Its Mangrove Capital Africa initiative is restoring large mangrove deltas across that continent, including the Rufiji Delta in Tanzania, and Senegal’s Saloum Delta, the largest mangrove deltas in East and West Africa, respectively. Hundreds of thousands of people depend directly on these forests for resources such as building materials, fish and oysters, and firewood, says WI technical officer Menno de Boer.

“In both sites, we work with the communities and local government to protect and restore mangroves, and help them to adopt sustainable approaches to mangrove resource use,” said de Boer, who works on WI’s deltas and coasts team. This includes using data and the latest technologies to identify where mangroves are disappearing, and allowing patrols to better target their efforts.

Mangrove reforestation project in Tanzania. Image by Léa Badoz/IUCN.
Mangrove reforestation project in Tanzania. Photo: Léa Badoz/IUCN.

“Threats in these deltas come from several sides,” he says. “Mangroves are being cut for firewood [and construction] and to make space for farming. On top of that, upstream developments [such as the Stiegler dam in Tanzania] threaten the freshwater and sediment flow, which is essential for the mangrove ecosystem.”

Other threats to mangroves worldwide include oil spills, as was seen earlier this year when the MV Wakashio bulk carrier sank off Mauritius, leaking fuel oil that devastated the country’s mangroves. Elsewhere, mangroves are being cleared to make way for aquaculture, one of the world’s fastest-growing food sectors, as well as for oil palm plantations and rice paddies. They are also being cleared for houses and hotels, developments that are associated with pollution.

Also read: Amphan in the Sundarbans: How Mangroves Protect the Coast From Tropical Storms

Wetlands International first trialed EMR in Guinea-Bissau’s Cacheu River Mangroves Natural Park in 2015. “It’s an approach that came up due to all the failing projects,” de Boer says. “Many projects that try to restore mangroves through just planting are not effective … they plant in the wrong place, the wrong species, the wrong density.”

While a gnarled forest of mangroves may look tough and resilient, different species need different conditions to thrive. Many have evolved special adaptions that make them suited to very specific environments, governed by factors such as salinity and sediment flow. Some mangroves, for instance, absorb oxygen through roots that grow out of the soil, and which can be smothered by too much sediment.

A mangrove in Puerto Rico. Photo: samycollazo/Flickr, CC BY 2.0

De Boer attributes the breakdown of many restoration projects to a lack of planning and a preference for species that are easy to plant over native species that would do better in the long term. Some mangroves produce viviparous seeds called propagules, which mature on the tree before they drop off. They can then be planted by simply pushing them straight into the mud. De Boer says that because of this, they became popular with planting schemes run by NGOs and private organizations; but these efforts failed to take into account the suitability of a species to a certain site, and as a result failed to restore functioning, self-sustaining forest.

Governments have often been part of the problem too, de Boer says, often pressing ahead with planting programs to meet targets but without ever really considering the outcomes.

Rethinking reforestation

Rather than simply planting thousands of mangroves in the hope that they will grow, EMR looks at the environmental conditions, and takes into account factors than have changed the hydrology of an area, such as fish ponds or rice paddies. It also encourages natural restoration, opening up deltas and allowing site-specific species to take hold, resulting in better survival rates, faster growth, and a more diverse, resilient forest.

Also read: Bullet Train Project to Cost Maharashtra 54,000 Mangrove Trees

In Guinea-Bissau, the hydrology of an area targeted for restoration had been disturbed by dikes and now-abandoned rice fields, which were preventing any tidal influence. Initial replanting efforts also used the wrong type of mangrove species. But once the dikes were broken, seeds from a different species were brought in on the tide and the forest started to grow back by itself. It was simply a case of letting nature take over, de Boer says. Not planting actually proved more successful, more efficient and much cheaper.

This article was originally published on Mongabay.

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