- A new analysis of satellite imagery dating as far back as 1972 reveals that mangroves in Madagascar are rebounding after decades of deforestation.
- The island’s total mangrove cover is down 8% compared with 1972, but a closer look at the data shows that the rate of loss has been declining and even reversed in the last decade.
- Between 2009 and 2019, Madagascar’s mangrove cover increased by 5%, with mangrove forests expanding even more in protected areas — showing that conservation efforts are working.
- Researchers say that mangroves still face many threats from climate change, deforestation and mining, and that continued engagement with coastal communities is critical to empower those communities to protect the local mangroves that they depend on.
Lalao Aigrette has worked to protect the mangroves of her native Madagascar for more than 16 years. Growing up inland, she didn’t see the ocean until she was around 20 years old. But now she works closely with coastal communities via the Madagascan environmental group Bôndy to help them steward the mangrove ecosystems they depend on. “Mangroves are really important for the coastal communities in Madagascar, for their livelihood,” Aigrette said. Now a new study has confirmed that Aigrette’s and others’ hard work has been paying off.
Mangroves have been hammered around the world in recent decades due to deforestation, pollution, climate change and other stressors. In 2007, the U.N. Food and Agriculture Organization estimated that the world lost about 20% of its mangrove forests between 1980 and 2005. Madagascar’s mangroves were heavily deforested during that time as well, spurring the government and other organizations to begin adding protections.
These efforts are beginning to work. A new analysis of satellite images in Global Ecology and Conservation, dating as far back as 1972, has revealed that Madagascar’s mangroves have been making a comeback, with rates of deforestation slowing over time and mangrove cover actually increasing over the last decade. While these vital ecosystems still face challenges, experts say the results are a sign that Madagascar’s efforts to protect mangroves have been succeeding.
“I definitely think that it can be seen as a success story,” said Temilola Fatoyinbo, a forest ecologist at the NASA Goddard Space Flight Center in Maryland, who was not involved with the study. “These protected areas, and conservation, work.”
Aigrette is not the only one who feels at home in the mangroves. These unique shoreline forests are hubs of biodiversity, hosting animal and plant species that can be found nowhere else, including the mangroves themselves. A mangrove is any tree or shrub that has evolved to thrive when partially submerged in saltwater; there are about 80 species total, and they aren’t all closely related.
Coastal mangrove forests can be found in tropical areas around the world, and they make up around half of Madagascar’s coastline. For communities living alongside mangroves, the trees and the ecosystem they create are a vital source of life.
Mangroves act as storm buffers, serve as fish nurseries and attract fish that are caught locally using traps and canoes and provide wood used for building, cooking and crafting the canoes.
Despite their importance, the overall status of Madagascar’s mangroves has long been unclear.
“There’s this really strong environmental degradation narrative about Madagascar,” said Dr. Rémi Bardou, a biogeographer at the University of Michigan and lead author of the new study, who pointed to the prevailing belief that humans have been heavily deforesting the island ever since they first arrived around 11,000 years ago. While Bardou said this myth of widespread destruction is ultimately untrue, humans have long been cutting down Madagascar’s mangroves, though estimates of how much mangrove forest is left can vary widely — from as low as 2,000 square kilometers (772.2 square miles) to as high as 3,000 km2 (1,158.3 mi2).
Bardou first began mapping Madagascan mangroves while working on his master’s thesis in France, focusing solely on the northwestern part of the island; it was then, in 2013, that he visited the island and saw that “a lot of coastal communities rely on mangroves” and “are actually really involved in maintaining them and protecting them,” he said. “I really was interested in looking at what’s actually happening in terms of both positive and negative dynamics.”
To get a fuller picture of that, Bardou turned to satellite imagery from NASA’s Landsat program, which started in 1972 with the launch of Landsat 1. The most recent satellite, Landsat 9, was launched in September 2021. Landsat’s image quality has improved over time, which can make comparing new images with old ones difficult, especially in tropical areas where land is often obscured by cloud cover.
Bardou scoured the database for the clearest images of the mangroves he could find, which ended up being during the dry season, between May and September. He was ultimately able to compare images from 1972, 1989, 1999, 2009 and 2019, allowing him to see how Madagascar’s mangrove cover has changed over nearly half a century.
“That’s a really impressive time range,” Fatoyinbo said. “It’s so great to see that long Landsat archive is being used.”
A high-level view of the results looks like bad news — Madagascar’s mangrove coverage decreased by about 8% between 1972 and 2019. But a closer look reveals that mangrove loss has been slowing over time, and that between 2009 and 2019, mangrove coverage actually increased by 5%. In 2019, mangroves covered 2,699 km2 (1,042.09 mi2) of Madagascar.
“It is true that mangroves have been deforested a lot in Madagascar,” Bardou said. “But then, since the year 2010, we kept seeing more and more positive dynamics.”
What’s more, mangroves rebounded most strongly within protected areas — an 8.7% increase compared with just 3% outside of these areas. Madagascar’s network of protected areas began in the 1930s and started expanding in the 1980s. Meanwhile, other conservation efforts led by nonprofits or grassroots organizations have grown in tandem. Aigrette’s former organization, Blue Ventures, replanted more than 9 million mangroves between 2014 and 2022, she said.
And in the coastal Ambanja district of northern Madagascar, 13 community groups came together to form the Fédération Miaramientagna, which spreads awareness about the importance of mangroves and promotes the use of sustainable wood from brown salwood tree (Acacia mangium) plantations as an alternative fuel source. Demand for charcoal, especially from urban areas in the north, is one of the greatest threats to mangroves.
“Not all of the people can afford gas for cooking,” Aigrette said, and mangrove wood is preferred for making charcoal over other kinds of trees.
The government banned the harvesting and selling of mangrove wood in 2014, but enforcement is lacking. In some areas, local communities enforce the ban themselves. But where this doesn’t exist, the federal government doesn’t have enough money or staff to protect the mangroves, Aigrette said.
Madagascar’s mangrove comeback aligns with results from other parts of the world too. In 2020, Fatoyinbo co-authored a study showing that global mangrove losses due to human activities are on the decline. This is partially because the easy-to-access mangroves have already been cut down, Fatoyinbo said, but is also because “the awareness and knowledge about the importance of mangrove ecosystems has just increased so much.”
As efforts to protect mangroves continue, Fatoyinbo expects the salt-loving trees to expand even further along the world’s tropical coasts.
While mangroves in Madagascar aren’t out of the woods yet — additional threats include mining, resort development and severe storms, which are becoming more common due to climate change — the new results show that with concerted conservation effort, in partnership with coastal communities, progress can be made.
“There is a need to empower the local communities to secure their rights over mangrove management,” Aigrette said, including not only the trees themselves but the fisheries they support. “Because their life is dependent on mangrove.”
Banner image: Lalao Aigrette conducts mangrove inventory training with coastal community members. Image courtesy of Lalao Aigrette.
Citations:
Bardou, R., Friess, D. A., Gillespie, T. W., & Cavanaugh, K. C. (2024). Assessing mangrove cover change in Madagascar (1972 to 2019): Widespread mangrove deforestation is slowing down. Global Ecology and Conservation, e03022. doi: 10.1016/j.gecco.2024.e03022
Rasolofo, M. V. (1997). Use of mangroves by traditional fishermen in Madagascar. Mangroves and Salt Marshes. Retrieved from https://link.springer.com/article/10.1023/A:1009923022474
Goldberg, L., Lagomasino, D., Thomas, N., & Fatoyinbo, T. (2020). Global declines in human‐driven mangrove loss. Global Change Biology, 26(10), 5844-5855. doi:10.1111/gcb.15275
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