Explained | How mangroves help in averting climate change risks

Mangrove forests stabilise coastlines and act as massive carbon sinks

Updated - November 15, 2022 04:35 pm IST

Published - November 12, 2022 05:45 pm IST

Mangroves in Sunderbans. (File photo)

Mangroves in Sunderbans. (File photo) | Photo Credit: AFP/Deshkalyan Chowdhury

The story so far: India joined the Mangrove Alliance for Climate on Monday, launched on the sidelines of the ongoing United Nations Climate Summit in Egypt. The alliance was launched by the U.A.E. and Indonesia, and India, Australia, Japan, Spain and Sri Lanka have joined it as partners.

“The integration of man.groves into the national programmes for reducing emissions from deforestation and forest degradation is the need of the hour. India can contribute to the global knowledge base due to its extensive experience in mangrove restoration, studies on ecosystem valuation and carbon sequestration,” Union Environment Minister Bhupender Yadav said.

What are mangroves?

Mangrove is a tropical tree, essentially adapted to thrive near the coastline, in brackish water and loose and wet soil. These trees cannot survive in colder temperatures.

A characteristic feature of mangroves is their tangled prop roots. These roots allow the trees to survive the daily tides and also capture sediments while slowing waterflow.

Estimated global mangrove extent for 2020 (in sq km) 

Estimated global mangrove extent for 2020 (in sq km)  | Photo Credit: The State of the World’s Mangroves 2022

Mangroves serve a multitude of purposes in their ecosystem, including coastal protection, filtration of water, and disaster risk reduction.

How do mangroves help in mitigating climate change effects?

Mangrove forests stabilise coastlines, reduce erosion, encourage biodiversity growth, and shield coastal communities from sea-level rise, and natural disasters like hurricanes and cyclones.

The 2022 State of World’s Mangroves Report, prepared by the Global Mangrove Alliance, finds that mangroves prevent more than $65 billion in property damages and reduce flood risk to some 15 million people every year.

Carbon sinks: Mangroves are one of the most carbon-rich forests of the tropics, storing carbon from the atmosphere at up to four times the rate of terrestrial forests. This makes mangrove forests an indispensable tool in achieving the goal of net zero carbon emissions by 2050.

Part of this carbon is stored in living biomass, while part of it is sequestered in the soil. Dead mangroves decompose very slowly due to waterlogging in the soil, making the accumulation of carbon in the soil last hundreds of years. The waterlogged soil is also a reason why mangroves hold more carbon than other forests, such as temperate or boreal ones.

According to The State of the World’s Mangroves Report, mangrove forests store around 6.23 gigatonnes of carbon (with an error margin of +/- 2.3). This is equivalent to 22.86 gigatonnes of carbon dioxide, with 87% of that being soil carbon. The loss of even 1% of the remaining mangroves will equate to over 520 million barrels of oil or the annual emissions of 49 million cars in the U.S.

Mangrove carbon by country and continent with areas scaled to total carbon

Mangrove carbon by country and continent with areas scaled to total carbon | Photo Credit: The State of the World’s Mangroves 2022

Indonesia, Brazil, Nigeria, Australia, and Mexico hold 50% of the total world mangrove carbon, mainly due to their large mangrove areas. Variations in carbon concentrations are also affected by environmental conditions. This is the reason why Nigeria is placed third in global rankings, primarily due to its rich soil carbon, even though Australia and Mexico have more mangroves by area.

Ecosystems: Mangroves usually do not exist in isolation but support interconnected terrestrial, freshwater, and marine habitats (think Royal Bengal Tigers, river dolphins, and crocodiles, all within each other’s vicinity in Sunderbans).

The roots of mangrove trees capture sediments, resulting in the formation of new, fertile lands. This process also ensures that offshore water is clearer, allowing marine life to thrive.

While mangrove creeks provide safe grounds for young fish, providing them food and protecting them from predators, they simultaneously provide rich feeding areas for predatory fish.

Disaster risk reduction: Not only do mangroves stabilise coastlines by holding sediments together but they also act as safety nets against storms and surges.

In tropical coastal areas, mangroves are the first line of defence against natural disasters like cyclones and hurricanes that originate in seas and oceans and impact land. Mangrove trees act as a buffer zone and arrest winds, slowing them down and hence minimising impact on land.

Socio-economic importance of mangroves

Mangrove ecosystems are home to a variety of fish. According to estimates, 4.1 million of the 52 million marine small-scale fishers worldwide fish in mangrove areas. This activity provides a critical source of jobs and protein to local, coastal communities. In Indonesia alone, mangroves are critical to an estimated 893,000 small-scale fishers. In Bangladesh and Nigeria, an estimated 82% and 89% of fishers respectively fish mainly in and around mangroves.

Mangroves are also important resources for timber and fuelwood, when collected sustainably.

In India, mangroves are found in the Sunderbans, which are extremely rich in biodiversity. The area, transformed into a national park, is also home to threatened or endangered species like the Royal Bengal Tiger, fishing cats, macaques, leopard cats, wild boar, flying fox, pangolin, and Indian grey mongoose. The biodiversity hotspot attracts thousands of visitors every year, generating valuable revenue.

Threat to mangroves

Agriculture, overfishing, and rapid urbanisation are some of the glaring threats to mangrove forests around the world. Indirect threats to mangroves include change in sedimentation rates and patterns, rising sea levels, and increase in pollutants, and these are often exacerbated by human actions.

In Kenya, overreliance on mangroves for fuel because of a lack of affordable alternatives, pollution from land-based sources, and conversion of mangrove areas to other land uses such as salt mining or settlements pose serious threats to mangroves. Similarly, deforestation for fuel is the biggest threat to mangroves in Madagascar too.

Mozambique lost more than 6% of its mangrove cover in the last 20 years, mainly due to the extraction of wood resources and deforestation to create land for saltpans and urban settlements. Solar salt production, which involves clearing and selective logging, altering microhabitats and microclimates, is also a threat to mangroves.

In India’s Sunderbans, salinisation, population pressure, and overexploitation are the primary threats to mangroves and the area’s biodiversity. The Sunderbans are sandwiched between a densely populated, poor rural area and a rising sea. These climatic and demographic challenges contribute to the degradation of the immensely fertile land and the biodiversity hotspot.

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