Mangrove forests are among the most carbon-dense ecosystems in the world and valuable sinks for carbon emissions released into the atmosphere. Now a global map of soil carbon in mangrove forests at 30 m spatial resolution could support new ecosystem services policy tools for rewarding the preservation of major environmental assets.

“We felt that working at 30 m resolution was critical because of the strong gradients that occur in mangrove forests across the tidal range,” says Jonathan Sanderman of Woods Hole Research Center in the US. “Within a few hundred metres, there can often be a two-fold variation in soil carbon stocks and we wanted to be able to capture this important local variance in soil carbon.”

Sanderman and colleagues developed a machine-learning based data-driven statistical model of the distribution of carbon density at key sites around the world. The tool integrates measurements of mangrove forests from hundreds of studies. The researchers hope it will play a major role in prioritizing conservation efforts and providing a baseline for carbon markets.

“For many nations, including most small island nations, mangrove protection and restoration represent one of the most viable climate mitigation options,” says Sanderman.

Running the model reveals areas of high carbon stock and regions where habitats are disappearing rapidly, helping to inform protection and restoration strategies.

From remotely-sensed data on mangrove forest cover change, the team reports a reduction in soil carbon of 30–122 Tg from 2000 to 2015. More than 75% of this reduction is attributable to deforestation in Indonesia, Malaysia and Myanmar.

A high-performance computing environment allowed the scientists to interpret large amounts of information; they used Google’s Earth Engine application to write the results to a webmap. The output can change on the fly as new data become available.

The researchers plan to offer an even more detailed picture of global carbon stocks. They are keen to understand the rate at which different mangrove forests build soil carbon, motivated by areas such as the Sundarbans on the Bay of Bengal.

“While they only store modest levels of soil carbon, the Sundarbans are likely a large sink because that carbon is being buried at a rapid rate due to the annual sediment load of the three rivers that feed into this large estuary,” says Sanderman. “We would like to develop an ability to predict and then map where high sequestration rates are occurring.”

The team published their work in Environmental Research Letters (ERL).