Mangrove restoration

Mangrove restoration nursery area, 2017. Photo by Barnes, R. https://www.flickr.com/photos/gridarendal/37333784240

Mangroves are adaptable plants that grow within shallow intertidal regions. Mangroves are adapted to deal with daily saltwater inundations. They filter out the salt with their root systems and the excess salt is secreted out their leaves. They have many environmental functions which wildlife species and humans benefit from.

Mangrove systems are located within shallow intertidal margins specifically in sheltered coastal and estuarine landscapes. Mangroves adapt to grow in harsh environments where most other plants can’t grow.

Name of NbS

Mangrove restoration

Type of NbS

Ecosystem restoration

Location

  • Urban
  • Periurban
  • Rural
Mangrove restoration in Mexico, 2013. Photo by Stone, A https://www.flickr.com/photos/usaid-biodiversity-forestry/12291292735

Relationship to Indigenous knowledge

Mangrove systems provide resources in many small island nations in Te Moananui Oceania including Aotearoa New Zealand. Traditionally Māori gathered food from mangrove forests, as well as using materials from the trees such as using lichen from the trees to make green dye or using mangrove leaves to keep caught fish cool on fishing trips (Northland Regional Council, 2024). Small island nations rely heavily on mangrove systems as they reduce wave energy from storm surges and act as a natural filter for pollutants (Madsa’ & Lopez, 2022).

Climate change benefits
  • Biomass cover loss
  • Coastal erosion
  • Loss of food production
  • Ocean acidification
  • Reduced water quality
  • Salt-water intrusion into aquifers
  • Sea level rise
  • Storm surge

Mangroves can sequester carbon dioxide and store this in their biomass and in organic soils where it can remain for thousands of years (Worthington & Spalding, 2018). Studies have found that mangroves with a more biodiverse set of plant species have a positive effect on mangrove biomass production and the ability to store carbon in the mangrove system soil (Bai et al, 2021). The sequestering and storing of carbon done by mangroves is called “blue” carbon (Sidik et al, 2017).

Mangroves trap sediment and organic matter in their root systems, which can contribute to the buildup of sedimentary carbonate minerals. These minerals can act as a buffer against acidification by increasing alkalinity in the surrounding water, helping to counteract the decrease in pH caused by the absorption of CO2. Mangroves help stabilise coastal sediments and protect shorelines from erosion and storm damage. Healthy mangrove forests can reduce the input of terrestrial organic matter and nutrients into coastal waters, which can help mitigate the effects of eutrophication; a process that can exacerbate ocean acidification by promoting algal blooms and subsequent decomposition.

The dense root systems of mangroves act as a physical barrier that can reduce the inland movement of saltwater. These roots can trap sediment and organic matter, forming a barrier that impedes the flow of saltwater from coastal areas into freshwater aquifers. Mangroves absorb water from the soil through their roots and release it into the atmosphere through transpiration. This process helps to lower the water table in mangrove areas, reducing the potential for saltwater to infiltrate underlying aquifers. Additionally, the uptake of water by mangroves can contribute to the dilution of seawater that may have infiltrated coastal soils.

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Societal / socio-cultural benefits
  • Disaster risk reduction
  • Food security and quality

Established mangroves can create benefits which include coastal protection from extreme climatic events and tsunamis.  Millions of people are protected from flooding annually by mangroves (Worthington & Spalding, 2018). The effectiveness of coastal protection when using restored mangroves depends on the dimension and location of the restored area (Worthington & Spalding, 2018). Along with coastal protection, they reduce flooding that has been driven by storm surges. Other benefits towards disaster risk reduction are the reduction of erosion and the support for vertical accretion of sediments helping to adapt to sea level rise (Worthington & Spalding, 2018).

Mangroves bolster food security through diverse means. They serve as vital nurseries for fish, nurturing numerous species that sustain coastal fisheries and provide protein for communities. Mangrove habitats support shellfish and crustaceans, enriching local diets and economies through fishing and aquaculture. Beyond seafood, mangroves offer wood for construction and fuel, along with non-timber forest products like honey and medicinal plants, diversifying food sources and generating income. Mangrove forests shield coastal areas from erosion and storm damage, safeguarding agricultural land and settlements, thus ensuring livelihoods and food security for coastal populations. By enhancing water quality and stabilising coastal soils, mangroves boost the productivity of adjacent ecosystems, further supporting fisheries and marine resources.

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Ecological and biodiversity benefits
  • Climate regulation
  • Disturbance prevention
  • Habitat provision
  • Purification

Mangroves are critical systems for many species of fish and wildlife. Once restored they can serve as a coastal fish and shellfish nursery habitat as well as produce a large capacity of leaf material which is a basis for a detritus food web (Worthington & Spalding, 2018). Mangrove systems have a complex structure of networks of channels and shallow pools that are bordered by interlocking roots (Worthington & Spalding, 2018). These characteristics play a role in the habitat provision of mangrove benefits.

Riverine mangroves once established or re-established can help remove pollutants through their root systems (Worthington & Spalding 2018).

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Technical requirements

To increase the chances of mangrove restoration being successful ongoing monitoring and management of the restored sites is necessary (Worthington & Spalding, 2018). This should involve monitoring the growth and survival of the restored areas as well as continuing with improved hydrological modifications along with supplementary planting and any weed removal if needed (Worthington & Spalding, 2018).

 Diagram illustrating several mangrove restoration techniques. Image by Gijon et al (2021).

Issues and Barriers

Restoring a mangrove system doesn’t just entail replanting mangrove species. There are the external issues surrounding mangroves that have had impacts on the deterioration of mangroves. This can include oil pollution, biological invasion, insect outbreak, and the influence of water transportation (Chen et al, 2009). There is also great pressure on mangrove systems from cities and towns. They are often removed to make way for coastal development.

Opportunities

There is an opportunity to add economic value to an area, with the benefits of increased fish and invertebrate species that can add wildlife for small fisheries.

Financial case

Evidence shows large ranges of values for the economic value of mangrove restorations. Flooding in relation to tropical storms leads to large economic losses for small island nations (Tri et al, 1998). This is where mangrove restoration plays an important financial role in mitigating this impact.

References
  • Bai, J., Meng, Y., Gou, R., Lyu, J., Dai, Z., Diao, X., … & Lin, G. (2021). Mangrove diversity enhances plant biomass production and carbon storage in Hainan island, China. Functional Ecology35(3), 774-786.
  • Chen, L., Wang, W., Zhang, Y., & Lin, G. (2009). Recent progresses in mangrove conservation, restoration and research in China. Journal of Plant Ecology2 (2), 45-54.
  • Gijón Mancheño, A., Herman, P. M., Jonkman, S. N., Kazi, S., Urrutia, I., & van Ledden, M. (2021). mapping mangrove opportunities with open access data: a case study for Bangladesh. Sustainability, 13(15), 8212.
  • Madsa’, B & Lopez, J (2022) Indigenous stewardship brings restoration of mangroves. Cultural survival. https://www.culturalsurvival.org/publications/cultural-survival-quarterly/indigenous-stewardship-brings-restoration-mangroves
  • Northland Regional Council (2024). Mangroves. Available online: https://www.nrc.govt.nz/for-schools/school-information-packs/mangroves/#:~:text=M%C4%81ori%20traditionally%20gathered%20food%20from,making%20kits%20and%20piupiu%20skirts. Date accessed 16 May, 2024.
  • Sidik, F., Supriyanto, B., Krisnawati, H., & Muttaqin, M. Z. (2018). Mangrove conservation for climate change mitigation in Indonesia. Wiley Interdisciplinary Reviews: Climate Change9(5), e529.
  • Tri, N. H., Adger, W. N., & Kelly, P. M. (1998). Natural resource management in mitigating climate impacts: the example of mangrove restoration in Vietnam. Global Environmental Change8(1), 49-61.
  • Worthington, T., & Spalding, M. (2018). Mangrove restoration potential: A global map highlighting a critical opportunity.

Further resources