The Can Gio Mangrove Biosphere Reserve, located in Vietnam’s Ho Chi Minh City, is one of the world’s largest areas of reforested mangroves.

BY MICHAEL TATARSKI ON 21 APRIL 2020

Mongabay Series: Global Forests

• A majority of the flora in the area was killed by defoliants sprayed by the U.S. Air Force during the Vietnam War.
• Today, the replanted forest protects the city from storms, and stores huge amounts of carbon dioxide, though development plans and aquaculture pose threats to Can Gio’s continued health.

HO CHI MINH CITY, Vietnam — As the largest urban area in Vietnam, Ho Chi Minh City is known for its kinetic pace of life, rivers of motorbike traffic, and relentless construction. With an official population of 9 million and a booming economy based on manufacturing, real estate and tourism, there is often little space for nature.

It may come as a surprise, even to many who live in Ho Chi Minh City, that one of the world’s great restored mangroves forests lies within the city’s borders.

The Can Gio Mangrove Biosphere Reserve covers 75,740 hectares (187,160 acres), and encompasses all of Can Gio district, the largest and one of the least populated of Ho Chi Minh City’s 24 districts. Can Gio sits between the central districts and the South China Sea, called the East Sea by Vietnam.

From above, it’s a surprisingly green stretch of land, especially compared to the gray tentacles of concrete that spread out farther from the city every day.

Inscribed as a UNESCO Biosphere Reserve in 2000, Can Gio includes a 4,721-hectare (11,666-acre) core area where human activity is strictly prohibited, a 41,139-hectare (101,657-acre) buffer zone where cultural and ecological development is allowed, and a 29,880-hectare (73,835-acre) transition zone where normal socio-economic development occurs. The area is currently only connected to the rest of Ho Chi Minh City by ferry, though a major bridge has been approved.

On the coast, tourism development is growing, in line with Vietnam’s increasingly wealthy middle class. Such construction will pose risks to the health of Can Gio’s mangroves in the future, but it’s something of a miracle that these forests exist at all.

Resurrection

Prior to the Vietnam War, known domestically as the American War, what is today Can Gio was home to a healthy natural mangrove ecosystem. According to a 2014 report from the International Society for Mangrove Ecosystems (ISME), from 1965 to 1969, the U.S. Air Force sprayed massive amounts of chemical defoliants on the area in an effort to deprive enemy forces of cover.

The result was devastating, with an estimated 57% of the area’s mangroves completely destroyed.

Following the war, parts of the surviving mangrove forests were cut down by local residents for fuelwood and construction material. By the late 1970s, 10,000 hectares (24,710 acres) remained barren, while only 5,600 hectares (13,840 acres) of forest were useable in any way.

In August 1978, the region came under the control of Ho Chi Minh City, formerly Saigon, and was renamed Can Gio. The municipal forestry department then undertook a massive reforestation program, planting 20,000 hectares (49,420 acres) of Rhizophora apiculata mangrove trees from specimens taken from the neighboring Mekong Delta.

Up until 1991, the replanted mangroves served as an economic forest for wood production, but Vietnam’s rise as a shrimp export powerhouse led people to clear mangroves for the creation of shrimp farms. In 1991, Can Gio became a coastal protection forest and strict regulations were put into place, and eventually the area “turned into one of the most beautiful and extensive sites of rehabilitated mangroves in the world,” according to the ISME report.

It was Vietnam’s first mangrove biosphere reserve, and the three primary management objects are “biodiversity conservation, environmentally-sound social, cultural and economic development, and mangrove-related training, research and education.”

Global mangrove experts who have studied Can Gio say they are impressed by how well-protected the reserve is.

Cyril Marchand, a professor of earth sciences at the University of New Caledonia, has researched mangroves in French Guiana, New Caledonia and Ho Chi Minh City, where he lived from 2013 to 2017. His focus was the role of mangroves amid climate change, and the presence of trace metals in mangrove forests.

“The mangroves are well-managed,” he said in a recent Skype interview. “There’s one management board, and if someone cuts trees, they use them and they replant — it’s like any use forest in the United States or Europe.”

A use forest is a forest utilized for logging or other economic benefits in a managed way.

“The restoration in Can Gio has been quite successful, because, even though the trees were deforested, the hydrology didn’t change, so they just had to replant and not restore the hydrology, which is a big problem in other mangrove areas,” Marie Arnaud, a Ph.D. researcher at the University of Leeds who spent six months in Can Gio, said in an interview. “They’re doing a good job of trying to protect this forest, too.”

One of these protective measures is to compensate people who live there for managing the forests, a system called payment for forest environmental service (PFES).

“They [the management board] hire people to check if others are deforesting the mangroves, and they give them a bit of money [725,000 dong, or $31, per month] and train them,” Arnaud said. “They’re quite well-integrated into the management of the park, and that’s a real strength. People in Can Gio are very proud of this mangrove forest, and I think that’s really important, that they see that mangroves are really valuable and if we destroy them, we destroy the benefits we get from them.”

Nguyen Thanh Nho, one of the faculty members at the environmental and food engineering department at Nguyen Tat Thanh University in Ho Chi Minh City and an expert on Can Gio, says Vietnam was the first country in Asia to launch a PFES policy on a national scale. However, it remains underutilized in Can Gio due to limited understanding of the role that mangroves play in environmental services.

This is highlighted in a 2012 report that includes a survey of 289 households in Can Gio. The researchers found that more than 80% of respondents understood the role mangroves play in protecting the area from storms, but only 20% were aware that mangroves filter the water that flows through them. Less than 50% of those surveyed recognized the important biodiversity habitats that mangroves contain, or their impact on local climate.

Nho says he believes this needs to change.

“I suggest that a comprehensive study be carried out to explore these services,” he said in an email. “With scientific data, we will explore the willingness to pay for potential environmental services, and get more people to offer such services.”

Current role

Today, Can Gio is key to protecting the greater Ho Chi Minh City region, including the heavily industrialized neighboring provinces of Binh Duong and Dong Nai, which has a population of more than 15 million and hosts some of Vietnam’s most important manufacturing facilities.

“The Can Gio Mangrove Biosphere Reserve plays a very important role,” Le Duc Tuan, executive secretary of the reserve under the municipal department of agriculture and rural development, wrote in an email. “It serves as the city’s ‘lungs’ by absorbing carbon dioxide and providing oxygen; it acts as the ‘kidneys’ by filtering wastewater pollution sent downstream from the city; and it is a ‘green wall,’ protecting the region from storms, typhoons and tsunamis coming from the East Sea.”

While tsunamis are exceptionally rare, the East Sea has a very active typhoon season, with numerous storms making landfall in Vietnam every year.

The ability of mangroves to store carbon means they also play a major part in reducing risk from future climate impacts, though when it comes to trees and forests in urban areas, not all are treated equally. “They are absolutely vital for climate change mitigation,” said Benno Boer, chief of natural sciences at UNESCO’s Bangkok office. “Especially natural mangroves should be conserved, and places where mangroves used to occur should be restored.”

Southern Vietnam is among the most vulnerable regions in the world when it comes to rising sea levels, and stretches of low-lying Ho Chi Minh City already flood easily during heavy rains or periods of especially high tides. To prevent this problem from getting worse, maintaining Can Gio’s health is necessary.

“Limiting shoreline erosion is a main role of mangroves related to climate change,” Marchand said. “Can Gio can protect Ho Chi Minh City from sea level rise, as the sedimentation rate in mangroves is high, so it’s possible that mangroves will keep pace with sea level rise.”

This would protect millions of people and billions of dollars’ worth of real estate in Ho Chi Minh City.

Future threats

Vietnam’s robust economic growth over the last two decades has created a substantial middle class, reaching an estimated 33 million people this year, according to the Boston Consulting Group. In 2018, Vietnamese took 80 million domestic trips, according to the Vietnam National Administration of Tourism, while 2019 saw 18 million international visitors, a new record.

Tourism is currently nonexistent due to the coronavirus pandemic, but this expansion of spending power and tourism has transformed much of the country’s coastline, as hotels, resorts and other tourism facilities have been built, sometimes damaging the very natural areas that attracted people in the first place.

While Can Gio’s core is very well-protected, there are areas of concern on its fringes. The design for the previously mentioned bridge linking the district to a neighboring district was approved last year, though no construction timeline is currently available. If built, this bridge would increase vehicle traffic, which largely uses one main road that runs from the ferry landing to the coast.

Much larger plans have also been proposed, including an extravagant blueprint from Japan’s Nikken Sekkei Civil Engineering Limited. This proposal includes a logistics hub, accommodation facilities within the mangrove forest, and a 2,870-hectare (7,090-acre) tourism development partially on reclaimed land along the coast. The planners also envision Can Gio with a population of roughly 600,000, whereas the current population is only about 71,000.

The project has not been approved, but it is one example of the scale of development that could occur in the area.

More immediate threats are shrimp farming, upstream pollution and erosion caused by the huge cargo ships that ply the Soai Rap and Long Tau rivers next to and through Can Gio on their way to and from Ho Chi Minh City’s busy ports.

Earth sciences professor Marchand saw the impact of shrimp farming in the reserve’s outer areas, where trees are cleared and the ground is drained to create shrimp ponds. “What I observed is that the core of the mangroves is really protected,” he said. “But on the edge, each time I went there were new projects, and I saw some mangroves which were destroyed.”

Such activity is evident on Google Maps, where square shrimp ponds have been carved out of sections of mangrove forest.

“The mangroves are located at the edge of the biggest industrial area in Vietnam,” Can Gio expert Nho said. “The river network acts as a unique gate from Ho Chi Minh City to the East Sea, and thus most development activities, including the pharmaceutical, packaging, textiles and electronics industries, as well as tourism and transport, along with rapid population growth, are inducing high pressures.”

These include something called eutrophication, when an excess of minerals and nutrients depletes oxygen from water, as well as erosion and the release of chemicals into the water and the sediment of the mangroves.

Can Gio’s poverty relative to other parts of Ho Chi Minh City poses a danger as well, according to the 2012 study discussed earlier. “Although reforestation programs were relatively successful, the problem still remains that poor people tend to generate their income by utilization of shortcoming direct values of mangrove forest (mostly resulting in extensive wood cutting) instead of long-term generated income through mangrove forest protection,” the report says. “Therefore, the improvement of local people’s livelihood is an important prerequisite to reduce pressure on mangrove forests.”

The bridge and potential developments discussed above would improve the livelihoods of many people but, as Marchand says, “When there is a lot of money involved, people don’t care about the environment.”

A model

For now, at least, Can Gio’s mangroves remain in good health, despite their proximity to a fast-growing megacity, making them unique almost anywhere.

“Can Gio is one of the largest reforested mangroves in the world,” Arnaud said. “You have a very mature forest, and what is interesting is that it’s huge, and it has been done at different time — so you have forest that was planted in 1975, other trees planted in the 1980s, and more in the 1990s, so you can use that to map the development of a forest. If you have part that was planted five years before another section, you can see how it evolves with age, and that’s quite unique.”

Marchand says he hopes the area can be modeled elsewhere. “Nearly 60% of the mangroves were destroyed … and because of the high sedimentation rate given the tides from the sea and the climate, the mangroves grew back very fast, and now it’s really beautiful,” he said. “You have some trees up to 20 meters [66 feet] high, there is natural regeneration with new non-planted species, there is good ecosystem function, and in terms of carbon storing, these mangroves store lots of carbon dioxide. It’s a big success.”