Why mangroves are so efficient at blue carbon sequestration

Mangroves are known to be one of the most efficient ecosystems in the world when it comes to removing carbon dioxide from the atmosphere. They achieve this because of the way they grow and function. The roots of mangrove trees are submerged in water, creating an oxygen-poor environment that slows the decomposition of organic matter. This leads to the buildup of organic carbon in the soil, which undisturbed can remain sequestered for hundreds of years.

Mangrove trees also have the ability to store carbon in their biomass. They grow faster than most other trees, and can store carbon at a rate of up to 4 times that of a tropical rainforest. This is because mangroves have a high leaf area index, which means they have a lot of leaves relative to their size. This allows them to capture more sunlight and grow faster, which in turn leads to greater carbon storage.

Mangroves can sequester up to 10 times more carbon per hectare than other terrestrial ecosystems, including tropical rainforests. This is due in part to the fact that mangroves have incredibly high rates of organic matter production and slow decomposition, which contributes to the accumulation of carbon in the soil and vegetation¹.

Mangroves are also more efficient than other coastal ecosystems such as seagrass meadows and salt marshes. While these ecosystems are important carbon sinks, they sequester less carbon than mangroves because they have lower biomass and slower rates of growth. Mangroves are estimated to store up to 4 times more carbon per hectare than other types of coastal wetlands, such as salt marshes and seagrass meadows².

Why do mangroves remain under threat?

Mangroves are threatened by human activities such as deforestation, aquaculture, and urbanisation. Protecting and restoring mangrove ecosystems is critical for their blue carbon sequestration potential and the many additional benefits they provide, including coastal protection, fisheries habitat, and biodiversity conservation.

Some of the main reasons that mangroves are being lost include: 

1. Habitat loss and degradation: Mangroves are often cleared for coastal development, aquaculture, and agriculture, which destroys their habitat and reduces their ability to provide important ecosystem services. 
2. Climate change: Rising sea levels, increased temperatures, and extreme weather events can have significant impacts on mangrove ecosystems, including changes in water quality, erosion, and saltwater intrusion.
3. Pollution: Industrial and agricultural pollution, as well as plastic and other debris, can harm mangroves and the organisms that depend on them.
4. Overfishing and unsustainable harvesting: Overfishing and unsustainable harvesting of mangrove resources, such as fish, crabs, and timber, can reduce their ecological and economic value.
5. Invasive species: Invasive species, such as the non-native red mangrove, can outcompete native species and alter the structure and function of mangrove ecosystems.
6. Lack of awareness and protection: Mangroves are often undervalued and lack legal protection, which can make them vulnerable to exploitation and destruction.

Overall, protecting and conserving mangroves is crucial for maintaining healthy coastal ecosystems and sustaining the livelihoods of millions of people around the world who depend on them for food, income, and other important resources. 

What role can mangroves play in blue carbon credits?

Mangrove conservation and restoration projects can generate carbon credits that can be sold in carbon markets. Carbon credits are a form of offset that allows companies and individuals to offset their carbon emissions by funding projects that reduce greenhouse gas emissions or remove carbon from the atmosphere. 

Increasingly it’s recognised that given their remarkable ability to sequester blue carbon, mangroves are an important tool in the fight against climate change. 

The value of the blue carbon stored in mangrove ecosystems has been estimated at between $1,000 and $9,000 per hectare per year, depending on the location and other factors. This suggests that protecting and restoring mangrove ecosystems can be an important economic opportunity for coastal communities, carbon project and carbon offset investors.³

The Blue Carbon Initiative estimates that the total carbon sequestered in mangroves globally is approximately 3.2 billion metric tons, which is equivalent to around 10 years of global carbon dioxide emissions from fossil fuel combustion.

How to effectively and sustainably restore mangroves

In spite of the numerous environmental, economic and financial benefits, mangrove restoration programmes often fail to deliver against the intended outcomes.  This is because mangrove restoration is a challenging and complex process which occurs over a number of years. Success is determined by the careful management of a wide range of factors over the entire restoration cycle.

1. Site selection: Choosing the right location for mangrove restoration is crucial. The site needs to have the right environmental conditions to support mangroves, including appropriate soil types, adequate water flow, and appropriate levels of salinity. A study published in the journal Restoration Ecology found that selecting the right site was one of the most important factors in successful mangrove restoration⁴.
2. Cost: Mangrove restoration can be expensive, as it involves many steps, including site preparation, tree planting, and monitoring. Additionally, the cost of maintaining the restored mangrove forest over time can also be high.
3. Lack of knowledge: There is still much to learn about the ecology and biology of mangroves, and their restoration. The complexity of the interactions between different species of mangroves, as well as between mangroves and other ecosystems, makes it difficult to predict the outcomes of restoration efforts.
4. Human interference: Mangrove ecosystems are under constant threat from human activities such as logging, agriculture, and urbanisation. These activities can cause damage to mangrove forests and make restoration efforts more difficult.
5. Seedling survival: While planting seeds or seedlings is a key step in mangrove restoration, ensuring their survival can be challenging. Seeds and seedlings may be vulnerable to predators or adverse environmental conditions, such as flooding, saltwater intrusion, and storms.
6. Long-term monitoring and maintenance: Mangrove restoration is a long-term process that requires ongoing monitoring and maintenance. Regular monitoring is needed to assess the success of the restoration effort and make adjustments as needed. A study published in the journal Marine and Freshwater Research found that ongoing monitoring and maintenance were critical for the long-term success of mangrove restoration projects⁵.
7. Community engagement: Community engagement is an essential part of successful mangrove restoration. However, engaging with local communities and building support for restoration efforts can be challenging, particularly if there is a lack of awareness about the importance of mangroves or competing interests for the land.

The mangrove restoration opportunity

Despite these challenges, mangrove restoration can be an important tool for mitigating the impacts of climate change and protecting vulnerable coastal communities. The benefits of restored mangrove ecosystems, such as increased biodiversity, coastal protection, and carbon sequestration, are significant. 

Therefore, efforts are needed to overcome the challenges associated with mangrove restoration, including increased funding, research, and community engagement. 

At Dendra we’ve developed a new mangrove restoration approach which combines the latest academic thinking, partnerships and our unique RestorationOS^TM technology to reliably restore and protect these vital ecosystems for future generations.

References:

1. Donato, D.C., et al. (2011). Mangroves among the most carbon-rich forests in the tropics. Nature Geoscience, 4(5), 293-297.
2. Fourqurean, J.W., et al. (2012). Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience, 5(7), 505-509.
3. Siikamäki, J., et al. (2012). Global economic potential for reducing carbon dioxide emissions from mangrove loss. Proceedings of the National Academy of Sciences, 109(36), 14369-14374.
4. Lewis, R.R. (2005). Ecological engineering for successful management and restoration of mangrove forests. Ecological Engineering, 24(4), 403-418.
5. Simard, M., et al. (2020). Advancing mangrove restoration science: a study of approaches and methods. Restoration Ecology, 28(S2), S204-S215