Planting mangroves can’t compensate for undisturbed mangrove forests

Planted mangroves can store up to 70% of carbon stock as compared to intact stands only after 20 years, finds a new study.
Planting mangroves can’t compensate for undisturbed mangrove forests
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CHENNAI: The ability of mangroves to store carbon has long been recognised, but little was known about whether planted mangroves can store carbon as efficiently as the naturally established stands and in which time frame.

However, this has been decoded by US-based researchers. It was found that planted mangroves can store up to 70% of carbon stock as compared to that found in intact stands after only 20 years. It emphasises the fact that the planted mangroves can’t replace or compensate for the ecological services delivered by an undisturbed mangrove forest.

This insight could significantly influence global efforts to restore and conserve mangroves, especially in the light of the alarming decline in these vital ecosystems over the past five decades.

These coastal forests, found in tropical and subtropical regions, play a crucial role in mitigating climate change by sequestering large amounts of carbon in their biomass and the surrounding soil. Their ability to trap carbon is essential in the fight against global warming, as it helps offset carbon emissions and stabilise atmospheric carbon dioxide levels.

The new study was spearheaded by Carine Bourgeois from the Forest Service’s International Programs office. Bourgeois and her team assembled an international group of mangrove researchers, including Rich MacKenzie and Sahadev Sharma, to lend their expertise. The team utilised logistic models developed from 40 years of data, which included nearly 700 planted mangrove stands worldwide, to measure carbon stock levels over time.

“About 10 years ago, Sahadev Sharma, then with the Institute of Pacific Islands Forestry, and I discovered that 20-year-old mangrove plantations in Cambodia had carbon stocks comparable to those of intact forests,” said MacKenzie, a scientist at the Institute of Pacific Islands Forestry. “This observation sparked our interest in investigating how widespread this phenomenon was and whether it could be a viable strategy for global mangrove restoration.”

The team’s findings were remarkable: after just 20 years, planted mangroves had achieved 71-73% of the carbon stock found in intact stands. This rapid accumulation of carbon highlights the potential for planted mangroves to serve as an effective tool in climate change mitigation, particularly in regions where mangroves have been lost due to deforestation, coastal development or natural disasters. It is estimated that along with historical losses, human-driven land use change, extreme weather events, and erosion wiped out 35% of the global mangrove area over the past five decades.

Part of their research work also involves monitoring mangroves to see how they’re faring. “Periodic and regular monitoring of mangroves can provide useful data on survival and success of restoration efforts and can help devise adaptive management strategies as and when needed,” Rupesh Bhomia from the Center for International Forestry Research and World Agroforestry (CIFOR-ICRAF), stated.

But MacKenzie warns that mangrove plantations are not always a solution for restoring the trees.

“Properly planned and implemented mangrove plantations are more effective at restoring carbon stocks than are degraded stands. However, this does not mean that mangrove plantations are always the best restoration method,” MacKenzie stated.

Planting mangroves is not a replacement, nor does it compensate for conserving intact stands, the researchers emphasised.

“Our models indicate that replanting in all highly restorable mangrove areas would absorb less than one percent of annual global emissions over 20 years. That’s why conserving existing mangrove stands is paramount,” Bourgeois emphasised.

Meanwhile, the International Union for Conservation of Nature (IUCN) has released the first global mangrove assessment, according to which more than half of all mangrove ecosystems are at risk of collapse by 2050. It says nearly 20% (19.6%) of the assessed mangroves are at high risk, classed as either Endangered or Critically Endangered, including that of South India, reflecting these areas are at severe risk of collapse.

The global assessment also claims that in the absence of additional conservation efforts, by 2050, about 7,065 sq km (- 5%) more mangroves will be lost and 23,672 sq km (-16%) will be submerged.

The study classified mangrove ecosystems in 36 different regions and assessed the threats and risk of collapse in each region. The work led by IUCN had active involvement of more than 250 experts based in 44 countries. “Mangrove ecosystems are exceptional in their ability to provide essential services to people, including coastal disaster risk reduction, carbon storage and sequestration, and support for fisheries. Their loss stands to be disastrous for nature and people across the globe,” said Angela Andrade, Chair of IUCN Commission on Ecosystem Management.

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