The mangroves in Cai Gio District hold a deep, dark secret. They are the only ones to have recovered from chemical warfare.
Formed in the large delta at the estuaries of three rivers—Dong Nai, Sai Gon and Vam Co—the Can Gio mangroves were almost completely destroyed during the Vietnam War by more than 4.5 million liters of the herbicide known as Agent Orange used mostly by the United States military.
More than half of the trees were destroyed. What was once a vast green forest turned into a desolate zone when the war ended.
"After 1975, most of the remaining trees were only one to two meters tall or there was only bare land. You could see all the way to the ships sailing in the sea even if you were standing very far away from the coast," recalled Associate Professor Vien Ngoc Nam of Nong Lam University, a scientist who has been involved in the restoration of the Can Gio mangroves for decades.
Today, the Can Gio mangrove forest accounts for 97% of the total forest area of Ho Chi Minh City, a bustling metropolis with nine million people. The mangrove forest, just more than 50km away from the hustle and bustle of Vietnam's largest city, not only serves as a shield against storms but also protects the capital against coastal erosion.
The trees also act as a "green lung" by absorbing carbon dioxide from pollution in the city, and as a "kidney" filtering water to the city and elsewhere.
An analysis of data compiled by Clark Labs at Clark University shows that the land cover of mangroves in the Can Gio forest has increased over the past 20 years.
It is apparent from the data that Ho Chi Minh City gained 8,450ha of mangroves from 1999 to 2018, and the province can now boast of the second highest rate of increase in mangrove area in Vietnam after Ca Mau.
But the picture is not as rosy as it seems in the recent past. The area for mangroves actually shrank by 2,530ha between 2014 and 2018. That accounted for 6% of land cover in the area in 2014.
Global Forest Watch found tree cover loss between 2016 and 2020, with last year being the worst yet. Tree cover, as defined by Global Forest Watch, is all vegetation with a height greater than 5m and loss can be due to various causes such as deforestation, mechanical harvesting, fire, disease or storm damage.
Alarming degradation in quality
A single species—Rhizophora apiculata—accounts for 97% of the mangroves in the Can Gio reserve after 43 years of reforestation and afforestation work.
"The first purpose of afforestation in Can Gio was to quickly green the area destroyed during the war. Rhizophora apiculata were planted in places where they can live. After the land for Rhizophora apiculata is no longer suitable, we have planted some other trees to diversify species," explained Professor Nam.
But scientists have been warning about the decline in the quality of the vegetation at Can Gio for more than 10 years after the People's Committee of Ho Chi Minh City "suddenly" decided to ban the thinning or pruning of the mangroves in 1999.
That decision has had unintended effects. Research on the quality of the single-species Can Gio mangrove forest in 2009 showed that forest quality and the water environment had declined.
A study by Professor Nam, published in 2014, compared the thinned or unpruned forest with an area where thinning was carried out. It showed that the thinned area absorbed nearly twice as much CO2 and the trees were healthier with larger canopy than before un-thinning.
Data from the past 20 years has also shown that although the ban on thinning may have contributed to an increase in mangrove area, it has been detrimental to the forest's overall health.
Livelihoods at stake
A report by Mr Huynh Duc Hoan and his colleagues at the management board of Can Gio Biosphere Reserve shows that the mangroves not only provide food, raw materials, timber, fresh water and medicinal plants. They also contribute significantly to the region's ecology such as through water purification, climate regulation, erosion control, species habitat support and genetic diversity.
The Can Gio mangroves have been critical to the livelihoods of many local people for decades. A report by the same management board, for instance, showed that the annual value of the nipa palm crop alone was about 158 billion dong (S$9.4 million).
"I have lived as a forest dweller for more than 20 years now," said Mr Nguyen Truong Hoa, a resident who makes a living by harvesting nipa leaves and fruits as well as by digging for crabs and snails. At night, he goes fishing with a net.
Without productive land to his name and with only limited education, Mr Hoa's livelihood, like that of 70% of his fellow villagers, depends on the mangroves. He makes about eight or nine million dong a month to support his family, which includes his wife and two school-going children. They scrape by.
But it is getting harder and harder to make a living, he said, because his haul of crabs, fish and snails has decreased by 50-70% over the last ten years. Natural shrimp and fish farming in the area is also failing.
Mr Nguyen Van Thang has lived in the forest by farming fish and shrimp for more than 20 years.
Taking advantage of the natural canals in the forest, he built embankments to keep the water in, creating a natural environment for shrimp and fish to grow. But over the years, the shrimps on his farm have become increasingly susceptible to diseases.
The farm extends over a total area of 6ha and Mr Thang said it would yield several tonnes of shrimp 10 years ago. That has now dwindled to only about 300kg to 400kg, he said.
Fishery resources are decreasing not only because of overcrowding and overfishing through modern technology, but also because of water contamination. There are various possible causes of contamination, including degradation of mangrove quality as proven by scientific reports.
Official statistics show that about four in 10 people living in Can Gio district are currently engaged in farming, fishing and agriculture.
In 2020, nearly 1,000 households were engaged mostly in aquaculture, salt production, oyster farming and fishing in the Can Gio mangrove reserve.
People from around the district and neighboring provinces also venture into the area to fish, among other things.
Experts disagree on what it will take to improve the situation, but most agree that the government's current ban on thinning must not only be lifted but also replaced by an aggressive restoration plan.
Mr Dinh Minh Hiep, deputy director of Ho Chi Minh City's Department of Agriculture and Rural Development, disclosed that it had already compiled a report on the thinning of the Can Gio mangroves, but top officials in the city administration had yet to officially respond to it.
Professor Nam believes the focus now should be on the areas where planting took place in the 1990s as part of a regrowth campaign. The mangroves on more than 20,000ha are now 43 years old, twice as old as a mature planted forest, and thinning is no longer an option, he said. He believes the entire area should be cleared in rotation and replaced with a variety of tree species to increase biodiversity, simulating a natural forest.
Biggest threat yet
Even as scientists scramble for solutions, the mangrove forest faces another existential threat. A 2,870ha land reclamation development project owned by Vingroup is slated for development in Can Gio district.
When completed, the 217 trillion dong project includes homes, a 108-storey skyscraper, a golf course and a cruise port. The Ho Chi Minh City government is convinced that the Can Gio Tourist City project will help improve the quality of life in the district as well as act as an impetus for the expansion of the city towards the sea.
But environmentalists have sounded the alarm on a variety of fronts. They say sand levelling and erosion could compound other environmental challenges for the city, including pollution, floods and landslides.
Many scientists have petitioned the prime minister to review and independently evaluate the entire land reclamation project.
An urban planning expert and architect, Mr Ngo Viet Nam Son, believes that the planning of Can Gio should be integrated into the overall urban planning of Ho Chi Minh City.
In particular, he suggested scaling back the Can Gio Tourist City project and steering it towards eco-tourism, turning it into a link in the chain of marine economic urban centers in the southern economic region.
The Can Gio mangrove forest will play an increasingly important role for Ho Chi Minh City in the face of climate change and sea-level rise. Violent storms in the South China Sea have been on the rise in both frequency and intensity and the forecast is for things to get worse for the capital.
"If the health of the mangroves is gone, the entire ecosystem of the region will be broken and negatively impacted. To restore, it will take a very long time," said Prof Nam.
Data used in this story
This story is supported by the Mekong Data Journalism Fellowship, jointly organised by Internews' Earth Journalism Network and the East-West Centre. It was originally published on 7 November 2021 in The Straits Times and has been lightly edited for length and clarity.
Banner image: The Can Gio mangroves have been critical to the livelihoods of many local people for decades / Credit: CTV.