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Optimising carbon mitigation and community benefits from mangrove ecosystems

Nguyen, Thi Hai (2021) Optimising carbon mitigation and community benefits from mangrove ecosystems. PhD thesis, Murdoch University.

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Mangroves are the association of trees and shrubs forming the dominant vegetation in tidal, saline wetlands, along tropical and subtropical coasts. Globally, mangroves have major latitudinal limits relating best to major ocean currents and the 200C seawater isotherm in winter. Mangrove forests are important ecosystems providing several marine based ecosystem services such as raw materials and food, fish nursery maintenance, water purification, coastline protection, carbon storage, erosion control and tourism. However, mangrove deforestation and degradation is a major issue with more than half of the global mangrove area lost during the past three decades from a range of causes.

Mangroves represent a large potential form of climate mitigation and adaptation via reforestation, and climate mitigation investment may contribute to protection and restoration efforts and reverse mangrove decline. This thesis explores how to optimise carbon mitigation and community benefits from mangrove ecosystems for future sustainable management of mangrove ecosystems. From this, future approaches for mangrove restoration projects are recommended to optimise both carbon mitigation benefits and other co-benefits for communities.

Over the last three decades there has been considerable state and non-government investment in mangrove restoration programs in Vietnam with c. 200,000 ha of mangrove restoration activity. A review of these projects (Chapter 2) provides indicators of the causes of project failure or success. Failure in some mangrove restoration programs in Vietnam can be attributed to poor site and species selection, lack of long-term monitoring and management, and lack of incentives to engage local residents in the long-term management of restored areas. The thesis suggests approaches for successful mangrove restoration activities in the context of current international agreements on climate change. These include improving site and species selection, establishing a baseline for restoration planning, adopting a robust monitoring and reporting process that inform the success or failure of restoration programs.

One of the important causes of failure of mangrove restoration projects in Vietnam is lack of long-term management of restored areas. Thus, engaging local residents in long-term management of restored mangroves is crucial. Chapter 3, examines different approaches of integrating mangroves and shrimp farming as a method of protecting mangroves by balancing economic, environmental and social objectives for local farmers who participate in mangrove protection. Using household survey data in Ca Mau Province (Vietnam), it was found that integrating mangroves with shrimp farming can support multiple objectives. Although the profit of intensive shrimp farming was around 20 times higher than the other extensive and mangrove-shrimp farming, mangrove-shrimp farming offers the highest rate of economic return (295%) as compared to both intensive and extensive shrimp farming systems with returns of 145% and 183%, respectively. Additionally, mangrove-shrimp farming also the least expensive and suitable for people with limited financial capacity. The analysis showed that mangrove coverage may contribute to the economic efficiency, and the optimal mangrove coverage from the perspective of individual farmers (30%) can be lower than what is demonstrated by empirical data (60%). Though undertaken in a specific location, the study highlights the benefits of mangrove-shrimp farming as a possible triple-win approach towards sustainable development, and it also emphasizes the importance of complementary programs, such as awareness enhancement, communication, and training.

Another important strategy for sustainable management of restored mangroves is to offer incentives for local communities. Currently, payment for carbon services (C-PFES) is proposed as an effective method to incentivize local people to participate in forest protection and enhance carbon sequestration to achieve emission reduction targets. However, carbon is a unique environmental service which is usually traded in international markets leading some challenges for implementation of C-PFES at the local level. Chapter 4 investigated the feasibility of applying C-PFES for mangroves in Ca Mau province, Vietnam. By collecting data from 73 stakeholders of three different groups, (potential sellers, potential buyers and intermediaries) the perceptions of stakeholders of climate change and the effects on their production were examined. While there was awareness of the environmental roles of mangroves, the carbon sequestration capacity of mangroves was rarely mentioned leading to challenges for implementing C-PFES scheme. While potential sellers and intermediaries showed strong support for C-PFES, only 29-56% of potential buyers considered to join the scheme. As carbon sequestration capacity of mangroves is also of interest to international entities, it is recommended that participation in a C-PFES scheme is broadened to include private companies, government agencies and international investors. The results from Chapter 4 can be applied as a case study in other countries with mangrove ecosystems where there are expectations of encouraging local participation in carbon offset markets.

One of the key considerations prior to the implementation of C-PFES for mangroves is to determine the carbon sequestration capacity of the mangrove ecosystem. Generally, mangroves are among the most important ecosystems in terms of storing large amounts of carbon per unit area. However, the carbon budget of mangrove ecosystems is complicated with inputs from mangrove primary production, the oceans and terrestrial sources. Additionally, there is a misperception in the investment and policy communities between carbon storage and carbon sequestration of mangroves leading to over-expectation of mangroves in climate change mitigation. In some literature mangroves are posited to be 2-40 times more effective than rainforests in carbon mitigation. Chapter 5 provides a critical overview of mangrove C sequestration and storage, and provides new insights into the role of restored mangroves in sequestering C from the atmosphere. Results showed that although mangrove C storage is much higher than other terrestrial ecosystems, due mainly to large stores in the soil and underlying sediment, the aboveground carbon sequestration rate is equal to that of tropical forests. Thus, there is not an advantage for mangroves to join in international carbon markets from the perspective of efficiency of carbon capture. However, mangrove ecosystems also provide many other production and environmental co-benefits and restoration will not displace productive farmland as happens with terrestrial reforestation. Instead of focusing on the single role of mangroves in sequestering C, co-benefits generated from mangrove ecosystems should be integrated and valued in restoration programs.

Overall, mangrove restoration is important in Vietnam where deforestation is a critical issue. Although there are some successful mangrove restoration projects, many programs in Vietnam have failed with low survival rates. Besides developing systematic monitoring systems, providing incentives to local residents may provide good solutions for the long-term management of mangroves. One approach is to promote mangrove-shrimp farming which can generate triple-win solution in environmental, economic and social aspects. Additionally, changing the awareness of local residents as to the benefits of mangrove coverage may contribute to protect mangroves, particularly if combined with environmental service payments. Here C-PFES, with the participation of multiple buyers, including the private sector, government and international investors, may provide a new income stream to improve the livelihoods for local communities to protect mangroves. Although carbon sequestration is emerging as an important climate change mitigation activity, mangrove restoration should be promoted in terms of its multiple environmental co-benefits. Determining how these cobenefits can be valued, and payments made to local communities, are priority for future work.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Agricultural Sciences
United Nations SDGs: Goal 14: Life Below Water
Supervisor(s): Harper, Richard and Dell, Bernard
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