By MIRIAM ACZEL
Brazil’s Amazon is home not only to the world’s largest tropical forest, but also one of the world’s largest mangrove areas. Mangroves are collections of different tree and shrub species found in tropical coastal regions, growing in waterlogged soils. They can be recognized because of their large roots protruding from soils—roots they use to ‘anchor’ themselves from strong incoming tides. There are over 80 distinct mangrove tree species, and can sequester or store large amount of carbon in their soils, which can be stored for multiple centuries. Deforestation of mangroves results in the release of sequestered carbon dioxide, as trees, plants, and soils release stored carbon once they are logged and cleared or burned. Although mangroves represent only 0.6% of global tropical forests, a new, long-term study published in the journal Biology Letters shows that these mangrove forests contain much more stored carbon than previously thought, and that their deforestation accounts for as much as 12 percent of greenhouse gas emissions produced by all tropical deforestation worldwide.
Mangroves are largely understudied, yet have been found to contain over 10 times as much stored carbon as the Amazon’s savannah, or grassy plains with sparse tree populations. While more focus has been placed on the Amazon’s nearly 170 million hectares of rainforests, this important new research sheds light on the crucial carbon storage capacity within the Amazon’s nearly 1 million hectares of mangrove forest.
Significant Carbon Storage in Mangroves
The study importantly demonstrates how mangrove deforestation contributes significantly to the greenhouse gas effect, one of the key causes of global warming. According to J. Boone Kauffman, the lead researcher from Oregon State University, the study found that coastal mangrove forests in the Amazon region sequester significantly more carbon per acre than the Amazon’s rainforests. According to Kauffman, “over 25 years, we found two to three times more carbon stored in the mangroves than in the rainforest…When those forests are cut down they lose carbon, creating far more greenhouse gases than when the rainforests are cleared. Mangroves deserve conservation and participation in climate change mitigation actions throughout the world.” This additional carbon is stored in mangrove biomass in the waterlogged soils, deep roots, and thick ‘aboveground’ topsoil containing slowly decomposing plant biomass.
During the study, researchers went to nine mangroves and three salt marshes in the Amazon state of Pará in Brazil. Salt marshes (coastal grasslands), like mangroves and sea grass communities, are referred to as “blue carbon” areas because they contain massive carbon storage. These habitats are particularly important to protect in order to mitigate climate change impacts.
At each of the sites, researchers measured of amounts of carbon stored ‘aboveground’ in the trees and fallen leaves, as well as the amounts of carbon contained ‘belowground’ in soils and plant roots. To determine the amount of carbon stock, scientists looked at changes in quantity of biomass or weight from new leaves and other growth production. Thus, because plants uptake, or take in, atmospheric carbon dioxide during photosynthesis processes to build and grow biomass including trunks, roots, and stems, scientists can use changes in the amount of biomass to estimate the amount of carbon stored per area over a certain time.
The study’s results demonstrated that the average Amazon mangroves store nearly twice as much carbon per hectare as that stored in Brazil’s Amazon evergreen forests. The study also found that the mangroves stored over eighttimes more carbon than the upland tropical dry forests, and that the salt marches contained twicethe carbon storage of the upland savannah grasses in Brazil’s Cerrado. The study also showed that the majority of carbon stored in mangroves is held in their waterlogged soils. Waterlogged soils in wetlands largely contain more carbon because the water volume slows decomposition rates of plant matter, slowing release of carbon.
Valuable Climate Change Information
So why is this study so important? The sheer expanse and size of Brazil’s mangroves means that there is a great potential in both mitigation of climate change as well as climate change adaptation strategies. Massive amounts of carbon are emitted due to mangrove deforestation, and enhancing our understanding of carbon storage in mangroves can play a key role in reducing global greenhouse gas emissions to mitigate climate change impacts. While much conservation focus has been dedicated to the Amazon’s rainforests, it is crucial to recognize and focus on the importance of mangrove conservation both for biodiversity preservation as well as climate change mitigation. Furthermore, mangroves provide other ‘ecosystem services,’ such as protection against storm and flood waters and control amounts of erosion. The mangroves also provide a buffer against salt water intrusion and serve as an important breeding and nursery area for fish and additional species.
Mangroves as ‘Kindergartens of the Seas’
Mangrove forests are also crucial for conservation of biodiversity—known as the “kindergarten of the seas,” juvenile fish species reproduce and spawn and spend the early part of their lives within mangroves. Mangrove conservation is also crucial to coastal protection—those living behind the mangroves are protected by the forests from storm surges. However, once they are cut down, those living in coastal communities become increasingly vulnerable to storms, flooding, and extreme weather events.
According to Kauffman, mangroves are also particularly “important for storm surge protection…when we destroy the mangroves, we make populations much more vulnerable to damage and death during hurricanes. More often these are some of the poorest people on the planet.”
Further research in Brazil’s mangroves, both for their valuable ecosystem services, rich biodiversity, storm and coastal protection, and carbon storage potential is key.
Miriam Aczel is a President’s Scholar PhD Candidate at Imperial College London’s Centre for Environmental Policy. Her research focus is on international energy science and policy, with a focus on mitigation of environmental and health impacts of shale gas. She is also co-founder and co-director of the Amir D. Aczel Foundation for Research and Education in Science and Mathematics, a nonprofit based in Cambodia.
Miriam is Director of Communications and blog editor for Leaders in Energy.