New Science: Mangrove Forests as Incredible Carbon Stores

Mangrove in Papua, Indonesia. Photo credit: Ethan Daniels.

Mangrove in Papua, Indonesia. Photo credit: Ethan Daniels.

Mark Spalding is a senior marine scientist at The Nature Conservancy.

My colleagues and I have just published a study in Conservation Letters in which we work out how much carbon there is in the world’s mangrove forests, give or take a bit.

And we mapped it.

And here’s why these findings are tremendously important:

They quantify what some of us in marine conservation have been saying for a decade or more: That mangrove forests are among the most carbon-rich habitats on the planet. That, although they occupy just a fraction of the world’s surface, they pack a punch.

Anyone concerned about preserving nature’s value — carbon sequestration and all the other benefits mangroves provide us — needs to think hard about this.

Because on average, mangroves have double the living biomass of tropical forests overall. This means that if you want to slow carbon emissions, one of the first places you could look would be in the mangroves.Stop an acre of loss here, and you will achieve a much bigger win than in many other areas.

But the average also hides a host of variance. Look at the map here and you’ll see that there’s a tenfold range in above-ground biomass:

Figure 1. Global mangrove map showing modeled patterns of above-ground biomass per unit area. Source: Hutchison et al. 2013.

Figure 1. Global mangrove map showing modeled patterns of above-ground biomass per unit area. Source: Hutchison et al. 2013.

So as we make our increasingly bold statements about the importance of mangrove biomass — or indeed around any ecosystem services — it is SO important that we have the numbers to back up our claims.

Until this paper, the best we could in most places was provide a global average number.  “A typical mangrove has 152 tons of aboveground biomass per hectare,” we might say.

That doesn’t sound at all convincing whether you are standing at the foot of canopy giant in Berau, Indonesia, or indeed on the margins of straggly community of mangrove shrubs in the desert margins of the Middle East.

To do this new paper, we stood on the shoulders of hundreds of others who have sweated and toiled in the tropical heat of the mangroves, doing the real work of assessing biomass.

We took numbers from 95 studies around the world and built a computer model around the climatic factors that help to drive the variability in biomass from place to place.

It’s a model, of course, and only captures part of reality, but it’s a huge advance. We need this sort of work — both the hard data from the field scientists and the verifiable models of what’s going on.

It means so much more than average numbers. Without it, all our platitudes and pleadings about the value of nature run the risk of sounding hollow.

The map shows the real hotspots for mangrove biomass. The countries of the Coral Triangle lead the way, but the overlap with coral reefs isn’t always neat — it’s the wet muddy coasts of Sumatra, Borneo, and New Guinea that have the very high biomass.

So, too, does an extraordinary stretch of coastline in on the Pacific coast of Columbia and Northern Ecuador. In all these places mangroves are truly breathtaking — gigantic trees with canopies reaching well over 30m high. These are found on wide, still growing deltas where they hold together sediments and add vast amounts of organic nutrients to the soils and the surrounding waters.

When it comes to soils, we’re still struggling with the models a bit, but the story is equally compelling. Most mangrove forests lay down peat — thick, heavy layers of carbon-rich soil that stays waterlogged and doesn’t rot.

There are other important peat forests worldwide, but the microbial processes in those peat forests give off pretty substantial amounts of methane, which is a greenhouse gas in its own right. The saline soils of the mangroves generally prevent this methane production. That gives us a huge extra carbon store in the soil.

But it’s not just a store. Mangroves are celebrated as one of the most productive ecosystems on the planet, and it is believed that about 10% of what they produce also gets sequestered away in the soil.

That word “sequestered” should be music to our ears. In other words, mangroves are natural carbon-scrubbers, taking CO2 out of the atmosphere and packing it away, for millennia or more, in their rich soils.

So 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. There’s no magic cure to the challenges of global change – warming, rising seas, worsening storms and ocean acidification – we’ll only ever get there through a combination of interventions. Mangroves aren’t sufficiently widespread to tip the scales, but they give a greater return on investment than many other mitigation efforts.

But on a unit-area basis, it would be hard to think of a more important ecosystem. And that’s before you even start to add up the value for fisheries, timber, tourism, coastal protection and so on.

This work was supervised by Dr. Mark Spalding, the lead author was James Hutchison, a researcher at the University of Cambridge now working with TNC on mangrove fisheries, and the other co-authors were other Cambridge conservation scientists: Andrea Manica, Ruth Swetnam (now at University of Staffordshire) and Andrew Balmford.

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.

Posted In: Marine

Mark Spalding is a senior scientist with the Conservancy’s Global Marine Team. He is based in the Conservation Science Group at the University of Cambridge. It’s a wonderful and sometimes awe-inspiring place to work—in the same block where Newton and Darwin worked, where the first computer was built and the double-helix discovered. He’s worked on big global studies of coral reefs and mangrove forests, but inspiration for all this work has come from the sheer thrill of being close to nature—be it an exotic coral reef or the pond in his garden.

Comments: New Science: Mangrove Forests as Incredible Carbon Stores

  •  Comment from Dexter M. Cabahug, Jr. UPLB, College, Laguna

    The above ground biomass per hectare is directly correlated to carbon stock as exemplified by gigantic mangrove trees in Sumatra,Borneo and New Guinea as well in Pacific Coast of Columbia and Northern Ecuador. We can still find virgin primary mangrove forest in the Philippines particularly along Ulugan Bay in Palawan and Northen Sierra Madre in Palanan, Isabela with Rhizophora apiculata and R. mucronata canopy reaching as high as 30 m. We can share our data to include in your analysis.

    Thank you

  •  Comment from Muljadi Tantra

    Great work Dr Spalding. I represent a company who has had 40 years experience in sustainable mangrove management (for woodchips). I enjoy reading your World Atlas of Mangrove and see that you are continuing to do some great work here. I hope some day you will be interested to come and visit our area (in Bintuni Bay). After 25 years, it is still as beautiful as it was and we have managed it sustainably. It is a pity to see how 1 million ha of mangrove forests destroyed in Indonesia through conversion (mostly Aquaculture). There must be a better way to improve the economy without destroying the environment for the next generation to come – especially now that we know how much carbon these forests can sequester.

  •  Comment from Dr. Kakoli Banerjee

    can you send me your published paper on evaluating the carbon credit in mangroves?

  •  Comment from Dr. Kakoli Banerjee

    You have done an excellent work. We too have a huge chunk of mangrove forest i.e. the Sundarbans. What type of analysis have you done for calculating the forest carbon? If you can share, we can be your partners in calculating for Indian Sundarbans.

  •  Comment from chintan bhagat

    It is brilliant work. I am working on the same. Can you mail me published paper or link for it?

  •  Comment from Dr. Kangkuso Analuddin

    This is nice opportunity to share experience research on mangroves. We are now doing research on blue carbon dynamics on mangroves forest at Rawa Aopa watumohai National Park, Indonesia. We establish allometric model for estimation of aboveground biomass and analyze the carbon and nutrient stock on mangrove ecosystems. We estimate carbon loss due to mangroves conversion or degraded mangroves

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