Protecting and Expanding Existing Mangroves

What are mangroves?

Mangroves are a collection of tree and bush species that are found along rivers, shores, and estuaries located in tropical or subtropical climates. Mangroves are notable for their roots, which give them the ability to thrive in salty water, which is formed by a mix of freshwater and twice-daily ocean tides. The greatest diversity of mangrove species can be found in Southeast Asia.^[1]

Figure 1: Map of world mangrove distribution. Source: Mangroves Florida Hawaii^[7]

Figure 2: Picture of healthy mangroves. Source: National Geographic^[2]

Mangroves have many ecological benefits, including:

• Providing breeding grounds for many fish, shrimp, crab, and shellfish species are located within mangroves.
  • Around 75% of commercially caught fish either have lived within mangroves or rely on food webs that have some connections to mangroves.^[3]
• Serving as a home to many different types of both land-dwelling and marine species^[3]
• Protecting the coastline
  • The roots of mangroves hold silt and sediment in place, which stabilizes shorelines against coastal erosion.
  • Small islands can actually be created when seedlings grow on sandbars, acting as another buffer against storm surges and heavy wind^[3]
• Maintaining clean water
  • The complex roots of mangroves filter nitrates and phosphates from water, which protects from eutrophication, along with keeping seawater from infiltrating inland waterways.^[3]
• Acting as a buffer zone from storms
  • Mangroves protect land from damage by rain and wind, meaning that places where mangroves have been destroyed are more vulnerable to tidal waves and cyclones.^[3]
• Providing commercial benefits
  • Mangroves can provide food, fishing grounds, fuel, medicine, tannins, and wood for humans.^[3]
• Sequestering Carbon
  • 1.5 metric tons/hectare/year is absorbed by mangrove forests.^[5]
• Supporting traditional practices
  • Traditional practices involving traditional medicines, wood fuel, building materials, and natural dyes come from mangroves.^[6]
• Combating ocean acidification
  • Ocean acidification, which is a decrease in pH caused when carbon dioxide dissolves in water, can be slightly curved by mangroves, which are one of the “largest natural sources of alkalinity to tropical coastal oceans”.^[8]

However, today’s mangroves are facing many hardships. By 2000, less than 50% of the world’s mangroves were intact. And about half of those intact were in poor condition.^[4] Every year, we are losing around 150,000 hectares per year, which is about 1% of global mangrove coverage a year.^[5] This land area equates to over 284,000 soccer fields. Shrimp farming, tourism, agriculture, coastal development, and charcoal and lumber industries are just a few of the ways humans are directly harming mangroves.^[4] However, the impacts of climate change are also indirectly affecting mangroves. Mangroves are the most productive within temperatures of 15°C to 25°C. At 35°C, roots and seedlings face thermal stress. When the temperature hits 38°C to 40°C, leaves stop photosynthesizing. With global warming and projected heat waves, this could hurt existing existing mangroves. Sea level rise as another product of climate change is another way that mangrove health could be put in danger. As the sea level rises and the coastline pushed inwards, mangroves will follow the coastline and also start to push inwards. However, if there are man-made structures in the way of mangrove growth, then the mangroves cannot continue to grow. Instead, the mangrove land area will become more narrow, lessening their ability to protect against flooding, strong winds, and storm surges.^[6] In addition, even though mangroves can help to combat decreasing seawater pH caused by ocean acidification, a seawater with a more basic pH can alter the pH of the soil that mangroves grow in, making the soil more basic. Mangroves growing in a soil that is too basic can end up dwarfed in size, lessening their ability to protect the coastline. The optimal pH range varies between mangrove species.^[9]

Figure 3: Effect of sea level rise and nearby man-made obstacles on mangrove growth. Source: MESCAL^[6]

The Sundarbans

The Sundarbans, located in the Bay of Bengal off the coast of India and Bangladesh, is the largest mangrove forest in the world. The low-lying Sundarbans covers about 10,000 sq. km of land.^[10]

Figure 4: Map of land area of the Sundarbans. Source: WWF India^[10]

There exist 24 native species of true mangroves (species that are found almost only in mangrove forests) in the Sundarbans, a UNESCO World Heritage Site:

Figure 5: Table of true mangrove species in the Sundarbans, which have the most growing success in the Sundarbans area, and their IUCN status. Source: J. Barik and S. Chowdhury^[11]

Video from the World Bank: Bangladesh Sundarbans – Helping Local Communities^[32]

Historically, the Sundarbans have been used by local communities for firewood, building materials, and a source of food, including honey. Since these locals were subsistence farmers, the mangroves were not exploited. However, during the shift away from subsistence farming and towards more commercial industries due to Bangladesh’s status as a developing country, exploitation of the Sundarbans began.^[28]

The positive benefits of mangrove forests in Bangladesh have been observed over the past few decades. In 1970, a typhoon hit Bangladesh and killed around 300,000 people. Had thousands of hectares of mangroves not been destroyed and replaced with rice paddy fields for short-term commercial gain, lives could have been saved. In addition, in a serious flood in Bangladesh in 1991, communities once again faced the brunt of floodwaters since 300 sq. km of mangrove had recently been cleared for rice cultivation and shrimp farming. The presence of mangroves play a crucial role in protecting the coastline of Bangladesh and buffering communities from storms and their effects. However, the dense growth of mangroves protected Bangladesh from the devastating impacts of a tsunami in 2005.^[12] Similarly, Cyclone Sidr in 2007 struck Bangladesh and killed about 3,000 people. However, the Sundarbans blunted the storm.^[13]

However, despite the lifesaving potential of the Sundarbans, its land area, like many other mangrove forests across the world, is shrinking in size. From 2000 to 2010, nearly 50,000 hectares of the Sundarbans has been encroached upon, a large portion of that being from shrimp farms. That amounts to about 8.3% of land lost from the Sundarbans’ northern front.^[14] Additionally, since the Sundarbans are considered to be “low island mangroves”, they have a lower rate of sedimentation than mangroves located on high land. Thus, the Sundarbans are more susceptible to sea level rise. Low island mangroves can adapt to the effects of rising sea level, but only if the rate of increase does not exceed 12 cm per 100 years. In contrast, high island mangroves can adapt to a rate of increase of up to 45 cm per 100 years.^[6] This, combined with the fact that there is a continuous, and natural, subsidence in the Sundarbans, which causes the sea level to rise by 2.2 mm every year, puts the Sundarbans in immediate danger. If the sea level were to rise by 45 cm worldwide, about 75% of the Sundarbans would be destroyed.^[15]

Unfortunately, despite the fact that the Sundarbans are shrinking, as the effects of climate change escalate, the Sundarbans will face an increasing reliance from coastal Bangladeshi communities. For example, as heat waves negatively impact crop yields in Bangladesh, more people will turn to other food options, which includes fishing. As a hotspot for biodiversity, mangroves are an excellent source of fish, shellfish, and other seafood. However, if mangroves are not thriving, communities are more vulnerable to starvation. On the other hand, if the use of crop selection and genetic engineering can successfully yield crops despite projected heat waves, mangrove forests are still crucial to protecting inland crops, and existing freshwater sources, from both saltwater inundation and wind.

Figure 6: Map of projected sea level rise in Bangladesh. Source: Rocky Rex Science^[16]

How can we increase the land area of mangroves in Bangladesh?

When is comes to increasing the land area of mangroves, both in Bangladesh and other areas of the world, there are two options:

1. Creating artificial, man-made mangroves
2. Protecting existing mangroves, taking the proper steps to ensure their health and growth
   

In areas with a strongly diminished or nonexistent mangrove population where previous attempts at mangrove restoration were not successful, artificial mangroves can be built. Artificial mangroves can be created in a variety of ways, including concrete structures built in a way that emulate the roots of mangroves, increasing biodiversity, providing a habitat for oysters, and helping clear water, or entirely planting a mangrove forest in a place where mangroves never grew or have been destroyed. Unfortunately, concrete mangroves cannot produce the same nutrients as true mangroves, and the success rate of entirely re-planting a mangrove forest is very low.^[17] In West Bengal, India, from the years 1989 – 1995, over 9,050 hectare of mangroves were planted. However, the success rate was only 1.52%. In the Philippines, over various planting sites, the success rate ranged from 0% to 60%. And since it can cost $225 to $216,000 USD to plant one hectare, risk is high.^[18]

Figure 7: Excerpt from the Smithsonian Institution Ocean Portal, “Mangrove Restoration: Letting Mother Nature Do The Work” ^[19]

Figure 8: Concrete mangroves off the coast of Florida. Source: WGCU^[17]

Fortunately for Bangladesh, there is still a hearty area (10,000 sq. km) of mangrove-rich land. Because of this, there is no need to completely rebuild mangrove forests. However, as mentioned earlier, the land area of the Sundarbans is decreasing. The best option to ensuring that the Sundarbans are healthy and capable of doing its job is to take action to preserve the existing mangrove forests. This can be achieved through maintaining mangrove health with the help of coastal Bangladeshi communities, the Bangladesh government, and non-governmental organizations (NGOs).

Mangroves consist of hardy plant species that can tolerate hostile living environments. Within a healthy environment, mangroves are able to recover and expand on their own, unlike man-made alternatives. When it comes to maintaining mangrove health, certain factors need to be monitored, the most important being hydrology (i.e. the flow of water). Although the exact number varies from species to species, mangroves tend to do their best when they are exposed to water 30% of the time (when tide comes in) and dry 70% of the time (when tide goes out).^[19] The mangrove restoration method that involves planting mangroves in areas where water exposure is most ideal (or manipulating land to make water exposure ideal) is called Ecological Mangrove Restoration (EMR).

In areas with a developing economy, such as Bangladesh, the cost per hectare of mangrove restoration is, on average, around $8,245 USD hectare. The median cost is $1,191 USD hectare. Thankfully, mangrove restoration projects are typically the least expensive per hectare than other marine coastal ecosystem restorations, such as salt marshes, coral reefs, and seagrass.^[21] The most common species of mangroves planted in the Sundarbans include Keora (Sonneratia apetala), Baen (Avicennia alba), Gewa (Excoecaria Agallocha), Rhizophora, Exochorda, and Ceriops.^[27] These species would be the main ones planted for mangrove restoration. The steps to EMR , which has been successfully implemented in Indonesia, Sri Lanka, Malaysia, Thailand, and Florida, is detailed in the image (from MangroveRestoration.com) below:^[20]

“Six Steps to Successful Mangrove Reforestation:

Work together with communities, organizations, and local governments to:

• Understand both the individual and the community ecology of the naturally occurring mangrove species at the site, paying particular attention to patterns of reproduction, distribution, and successful seedling establishment.

• Understand the normal hydrology that controls the distribution and successful establishment and growth of targeted mangrove species.

• Assess the modifications of the mangrove environment that occurred and that currently prevent natural secondary succession.

• Select appropriate restoration areas through application of steps 1-3 that are both likely to succeed in rehabilitating a forest ecosystem and are cost effective. Consider the available labor to carry out the projects, including adequate monitoring of their progress towards meeting quantitative goals established prior to restoration. This step includes resolving land ownership/use issues necessary for ensuring long-term access to and conservation of the site.

• Design the restoration program at appropriate sites selected in step 4 to restore the appropriate hydrology and utilize natural volunteer mangrove recruitment for natural plant establishment.

• Utilize actual planting of propagules or seedlings only after determining through steps 1 – 5 that natural recruitment will not provide the quantity of successfully established seedlings, rate of stabilization, or rate of growth as required for project success.

Local communities plant propagules and/or seedlings even after having undertaken EMR for a combination of five reasons:

• impatience

• planted areas appear to outsiders (not aware of the project) as intentional actions and provide a measure of protection, as it is obvious that there is human activity in the area

• promotion of growth of “preferred” species, such as Rhizophora

• to encourage and ensure local community participation in restoration efforts, as direct involvement may inspire better stewardship and a keener sense of project ownership by local communities

• to earn income, as some NGOs and government agencies specifically budget funds for planting mangroves regardless of actual need at given project sites”^[20]

Video from Al Jazeera English: Details the Mangrove Action Project^[33]

In addition, if earthen dikes are built, mangroves can also be incorporated, as seen in this video from Wageningen University & Research:^[34]

What is currently being done to help the Sundarbans?

In order to successfully increase the land area of the Sundarbans, invested parties–which include local Bangladeshi communities, the government, and NGOs–will need to cooperate with one another. However, it is advantageous to first take a look at what is currently being done and then analyze whether those strategies are working, followed up with suggestions for areas of improvement.

• From Bangladesh’s government:
  • In August 2017, the government made the decision to increase the proportion of land off-limits to people from 23% to 52% (3,129 sq. km to 2,323 sq. km).^[22] There is also the Forest Department of Bangladesh. It is in charge of protected areas, which includes parts of the Sundarbans.^[27]
• From third-parties (such as NGOs):
  • US Agency for International Development (USAID):
    • USAID works alongside the Bangladesh Forest Department and Local Communities to promote mangrove restoration through planting seedling.^[23] USAID also funds Winrock International’s Climate Resilient Ecosystems and Livelihoods (CREL) project.This project has transformed 450 hectares of land into mangrove forests by distributing 200,000 saplings to villagers and paying them to plant them. Not only does this help rebuild forests, but it also provides local communities with jobs.^[26]
  • UN Development Programme (UNDP)
    • UNDP trains and employs local people to run mangrove nurseries and manage forests.^[24]
  • Sundarbans Mangrove Biodiversity Education Program
    • This program was implemented by Japan Environmental Education Forum (JEEF) and the Bangladesh Environment and Development Society (BEDS). It teaches students, teachers, and communities in Bangladesh about sustainability and conservation in respect to the Sundarbans. Their teaching materials include booklets, games, and documentaries, which can be found in 82 primary schools in Bangladesh. The Bangladeshi government is considering using information from this program as a supplementary textbook in schools.^[25]

In summary, a bulk of the efforts that are being done to preserve and replant the Sundarbans are being headed by NGOs. The NGOs that have the most success are the ones who involve local people, since they, and their children, are the ones who will continue to look after the mangroves in the long run. However, while the hard work of NGOs is paying off, they are not able to reach all areas of coastal Bangladesh.

Figure 9: Utilizing community-based adaptations to ensure the long-term health of the Sundarbans, Image from author.

Currently, 2,585 sq. km (out of approximately 10,000 sq. km) of the Sundarbans is part of a protected area called the Sundarbans National Park.^[10] The Bangladeshi government needs to not only continue to protect this land, but also expand its protected areas. In addition, Bangladesh will need to communicate with India since the east coast of India is also bordered by the Sundarbans (See Figure 4: Map of land area of the Sundarbans). Considering that 70% of Bangladeshi citizens view India favorably, this cooperation for the sake of the Sundarbans should be accepted by the Bangladeshi public.^[30] As the amount of land covered by mangroves increases due to successful restoration projects, the area of protected land needs to also increase proportionally. In addition, the government also needs to discourage potential sources of pollution, such as factories and power plants, from being constructed next to mangroves, whether that land is protected or not. While mangroves may be hardy, with changing sea level, salinity, and pH, they will be more vulnerable to other damaging factors. As the mangroves prosper and grow, there may be opposition from those who have benefitted from the destruction and/or exploitation of mangroves, such as those who own commercial rice paddies or shrimp farms. However, if the government could take a stronger stance against mangrove exploitation and destruction and the industries responsible for that, while also creating policies to further protect mangroves and encourage their preservation and regrowth, the Sundarbans would be a healthier, more effective barrier against the impacts of climate change.

NGOs, such as USAID, UNDP, and WWF India, and other third-parties invested in the health of the Sundarbans should continue to financially support programs that not only improve the health of mangroves, but also empower Bangladeshi citizens with knowledge about mangroves and long-term jobs that involve caring for mangroves. If communities can build economies and lifestyles that depend on the health of the Sundarbans, the mangroves will have a stronger voice advocating for them. By teaching locals to view the Sundarbans as a place that is capable of providing for them if cared for correctly, individuals such as subsistence farmers can continue to gather firewood, honey, and other resources in minimal amounts without worrying about hurting the mangroves.

If the government, local communities, and third-parties can work cooperatively and successfully implement EMR, bare land that once held mangroves can see signs of regrowth in just 27 months. By around 78 months, the land and its mangroves are fully recovered and will continue to prosper on their own.

Figure 10: EMR Timeline. Source: MangroveRestoration.com^[20]

Protecting Mangroves Is a Win for Everyone

Mangroves have the unique ability of being to both protect and provide for their communities, but only if they are properly taken care of. Ecological mangrove restoration not only provides a long-term and sustainable solution to protecting coastal Bangladeshi communities from the impact of climate change, such as sea level rise, coastal erosion, saltwater inundation, storm surges, and strong winds, but is also less expensive than building manmade structures such as floodwalls and levees, which can cost anywhere from $.5 million to $7.5 million USD per linear mile.^[29] And while mangroves can help coastal Bangladesh face the brunt of climate change, mangroves also play a part in helping to mitigate climate change, which is a beneficial component to look at in the long run. Everyone invested in the health of the Sundarbans, which range from foreign organizations and scientists to the Bangladeshi government and its local citizens, must band together to implement EMR and restore the health of mangroves, which are an essential part of preparing coastal Bangladesh for the effects of climate change.

By Kayleigh Dugas

 

References

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