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World-first study challenges impact of net mangrove loss on climate change

A new framework developed by Monash University and ETH Zurich is challenging the widely held belief that mangrove deforestation has been a significant contributor to climate change over recent decades.

Mangrove forests are coastal ecosystems that are famous for storing large amounts of carbon in the trees and soil.

Historically, mangrove deforestation was responsible for huge emissions of carbon into the atmosphere, however, over the past decade or so, mangroves have been the focus of many conservation and restoration projects, aimed at keeping the carbon locked up. 

Previous estimates of changes in global mangrove carbon stocks only considered the negative effects of deforestation, but not the possibility that new mangroves would grow, and that not all carbon would be released following their conversion. 

However, a group of researchers from ETH Zurich and Monash’s Faculty of Arts have developed a world-first method that accounts for the expansion of mangroves through natural and human forestation, and carbon that remains in the ecosystem following mangrove deforestation. 

The pioneering study, published last night in the prestigious Nature Communications journal, found carbon loss estimates were 66 per cent lower than using the assumptions of previous models.

It quantified the net loss of mangrove carbon stocks globally between 1996 and 2016, finding a decline of only 1.8 per cent, equivalent to less than 0.1 per cent of global CO2 emissions over the same period.

The new method developed by the researchers takes advantage of improved global datasets on mangrove coverage and carbon densities, as well as recent studies quantifying how much carbon is lost when mangroves are converted to other land uses such as agriculture and aquaculture.

Monash University Lecturer in Human Geography, Dr Benjamin Thompson, said the low net loss of mangrove carbon stocks was surprising to the researchers.

“Mangroves are often presented as an ecosystem that is experiencing an ongoing crisis, but our study is one of several recent pieces of work showing that actually there has been a lot of success in reducing deforestation rates around the world,” he said.

“In addition, new mangrove forests are growing in some areas. We found that in some parts of Mexico and Myanmar, there was more carbon stored in mangroves in 2016 than in 1996.”

Dr Thompson said despite the apparent success of conservation efforts in protecting mangroves from deforestation, it was important not to be complacent. 

“Mangroves hold some of the highest densities of carbon reported in any ecosystem, but their conservation and restoration still require considerable management effort and investment to maintain these low rates of net loss,” he said. 

Researchers said it was also possible that lessons can be learnt from mangrove conservation and restoration activities to help other ecosystems such as tropical peatlands, which have seen much higher rates of net loss in recent decades.

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