Tropical wetlands and REDD+: Three unique scientific challenges for policy

The carbon sequestration and storage value of terrestrial habitats is now increasingly appreciated, and is the basis for Payment for Ecosystem Service (PES) policies such as REDD+. Tropical wetlands may be suitable for inclusion in such schemes because of the disproportionately large volume of carbon they are able to store. However, tropical wetlands offer a number of unique challenges for carbon management and policy compared to terrestrial forest systems: 1) Tropical wetlands are dynamic and subject to a wide range of physical and ecological processes that affect their long-term carbon storage potential – thus, such systems can quickly become a carbon source instead of a sink; 2) Carbon dynamics in tropical wetlands often operate over longer time-scales than are currently covered by REDD+ payments; and 3) Much of the carbon in a tropical wetland is stored in the soil, so monitoring, reporting and verification (MRV) needs to adequately encapsulate the entire ecosystem and not just the vegetative component. This paper discusses these physical and biological concepts, and highlights key legal, management and policy questions that must be considered when constructing a policy framework to conserve these crucial ecosystems

Patterns of mangrove forest disturbance and biomass removal due to small-scale harvesting in southwestern Madagascar

Abstract: Informal small-scale mangrove wood harvesting has received limited attention, though it is a widespread threat to mangroves in many parts of the tropics. We investigated wood use and the impacts of harvesting on mangrove forests in the Bay of Assassins in southwest Madagascar. We measured forest structure, composition, and harvesting across 60 vegetation plots and investigated human uses of the mangroves through Rapid Rural Appraisal techniques. We found that unlike other mangroves in the region, those in the Bay of Assassins are dominated by Ceriops tagal. Tree harvesting rates are high, with a mean of 28.7% (SD 19.4) of trees harvested per plot. This is similar to heavily harvested mangroves in other parts of the tropics. A comparison of tree versus sapling importance of the different mangrove tree species indicates that the composition of the mangrove forest is changing, with C. tagal becoming more important. Livelihood activities drive the harvesting of certain species and size classes. Mangrove wood is used mainly for the construction of traditional housing and fencing. There are also emerging uses of mangrove wood, including seaweed (Kappaphycus alvarezii) aquaculture and the production of ‘sokay’, a lime render made by burning sea shells in mangrove wood kilns and used to improve the durability of houses. Small-scale selective harvesting of mangrove wood is important for local livelihoods but may have wide-ranging impacts on forest composition and structure. Demand for mangrove wood has grown in relation to new commodity chains for marine products, demonstrating the need for integrated landscape management that considers wetland, terrestrial and marine resources together

Ecotourism as a Tool for Mangrove Conservation

Intertidal mangrove forests cover much of the coastline of Southeast Asia, provide crucial ecosystem services to millions of people living in the coastal zone, and are some of the most biodiverse in the world. However, they are one of the most threatened ecosystems in the tropics due to land cover conversion to agriculture (rice, oil palm) and aquaculture. Several conservation tools have been suggested to reduce mangrove deforestation, with many recent tools based on financially valuing the mangrove ecosystem and using that money to incentivize habitat protection. An important set of ecosystem services that can potentially be paid for under some settings are cultural values, such as recreation, tourism, spiritual value and aesthetic value. Ecotourism potentially represents a set of sustainable tourism principles that utilize the cultural ecosystem services of habitats to provide income to tourism operators and local communities. While we don’t yet have a comprehensive and large-scale overview of the full extent of mangrove ecotourism activities in the region, numerous case studies suggest the importance of these activities in bringing mangroves and people together. However, ecotourism must be implemented correctly in order to minimize the adverse impacts of tourists on local habitats. These impacts can be physical, including increased shoreline erosion, noise and pollution, or social, including the exclusion of local tour operators and communities. We need to understand these impacts, and how to reduce them, if we want to better conserve mangrove forests using neoliberal approaches such as ecotourism

Ancient high-energy storm boulder deposits on Ko Samui, Thailand, and their significance for identifying coastal hazard risk

© 2016 Elsevier B.V. Coastal geomorphic processes associated with high-energy storm events are difficult to estimate over recent geological history, though their frequency and magnitude are important to assess in order to understand present-day coastal vulnerability. Studying ancient coastal boulder deposits can shed light on the previous physical conditions necessary for their deposition. In this study, we estimated the physical processes required to move reef-derived coral boulders on the east coast of Ko Samui, a rapidly developing tourist island off eastern peninsular Thailand. The position and dimensions of 97 coral boulders (weight: mean 2.9. t, max. 12.7. t; transport distance: max. 125. m) were measured at two sites and dated using uranium/thorium methods. Flow velocities of 2.3-8.6. m/s were required to transport the measured boulders, with individuals deposited up to 4.7. m above mean sea level. Age-dating suggests that events capable of the highest flow velocities occurred around AD 1600 and AD 1750. These were probably driven by tropical cyclones (typhoons). Boulder transport by events of similar magnitude has not been detected within the last 250. years. The non-occurrence of similar events in living memory has implications for hazard perceptions at this important tourist destination. However, there is also evidence of substantial Holocene sea-level changes in the Gulf of Thailand, as observed at nearby Ko Phaluai. This potentially offers a challenge for the interpretation of older boulders dating from the mid-Holocene, as sea level may have been more than 2. m higher than present. Thus, studies using coral boulders as a proxy for past storm-wave conditions must consider the broader sea-level history, and are probably best limited to the period post-2000. BP in the Gulf of Thailand

Indicators of scientific value: An under-recognised ecosystem service of coastal and marine habitats

Coastal ecosystems provide a broad range of ecosystem services, which can be used to justify habitat conservation. The cultural ecosystem services of coastal ecosystems are generally underappreciated, and this is particularly the case when quantifying their scientific value. We created a tiered set of indicators to quantify scientific value spatially, and tested them using the case study of the island nation of Singapore. We conducted a systematic review of research papers, book chapters, conference reports and academic theses produced across 10 coastal ecosystems in Singapore, including mangroves, seagrasses, coral reefs, beaches and artificial coastal structures. At least 656 articles have been produced on Singapore’s coastal zone, with 2201 unique observations, showing that scientific value is spatially variable along Singapore’s coastline. Novel indicators such as the Site Impact Factor are able to differentiate scientific value between sites. This method has shed light on an under-recognised, but important cultural ecosystem service, and is applicable to other spatially-bounded coastal, marine and terrestrial landscapes

Chapter 3 Ecosystem Services and Disservices of Mangrove Forests and Salt Marshes

Coastal wetlands such as mangrove forests and saltmarshes provide a range of important benefits to people, broadly defined as ecosystem services. These include provisioning services such as fuelwood and food, regulating services such as carbon sequestration and wave attenuation, and various tangible and intangible cultural services. However, strong negative perceptions of coastal wetlands also exist, often driven by the perceived or actual ecosystem disservices that they also produce. These can include odour, a sense of danger, and their real or perceived role in vector and disease transmission (e.g., malaria). This review provides an introduction to the ecosystem services and disservices concepts, and highlights the broad range of services and disservices provided by mangrove forests and saltmarshes. Importantly, we discuss the key implications of ecosystem services and disservices for the management of these important coastal ecosystems. Ultimately, a clear binary does not exist between ecosystem services and disservices; an ecosystem service to one stakeholder can be viewed as a disservice to another, or a service can change seasonally into a disservice, and vice versa. It is not enough to only consider the beneficial ecosystem services that coastal wetlands provide: instead, we need to provide a balanced view of coastal wetlands that incorporates the complexities that exist in how humans relate to and interact with these important coastal ecosystems

Geomorphic Gradients in Shallow Seagrass Carbon Stocks

Seagrass meadows are important sinks of organic carbon (Corg), in particular the near-surface Corg pool (≤ 15 cm) compared to deeper sediments. Near-surface carbon is highly susceptible to disturbance and loss to the atmosphere, however, inadequate accounting for variability in this pool of carbon limits their uptake into carbon accounting frameworks. We therefore investigated the spatial variability in seagrass near-surface Corg and biomass Corg across different geomorphic (estuary, lagoonal and reef-associated) and community typologies (pioneer and persistent). Near-surface Corg stock in vegetated areas (25.78 Mg Corg ha−1 ± 26.64) was twice that from unvegetated areas (14.27 Mg Corg ha−1 ± 15.86), reinforcing the paradigm that the presence of seagrass enhances carbon stocks. Lagoonal and reef-associated meadows showed similar Corg stocks (p \u3e 0.05), which were substantially higher (p \u3c 0.05) than estuary meadows. Likewise, persistent seagrass communities (Cymodocea dominance) stored higher (p \u3c 0.05) stocks of Corg than pioneer communities (Halophila and Halodule dominance). Linear regression models showed significant but weak relationships between seagrass cover, shoot density and standing biomass with near-surface Corg stocks, whereas significant and strong relationships were observed for organic matter, dry bulk density and median grain size. The results highlight the need for higher resolution carbon assessments to better understand local and regional variability, in order to better inform carbon accounting and conservation policy

Blue carbon as a natural climate solution

Blue carbon ecosystems (BCEs), including mangrove forests, seagrass meadows and tidal marshes, store carbon and provide co-benefits such as coastal protection and fisheries enhancement. Blue carbon sequestration has therefore been suggested as a natural climate solution. In this Review, we examine the potential for BCEs to act as carbon sinks and the opportunities to protect or restore ecosystems for this function. Globally, BCEs are calculated to store \u3e 30,000 Tg C across ~185 million ha, with their conservation potentially avoiding emissions of 304 (141–466) Tg carbon dioxide equivalent (CO2e) per year. Potential BCE restoration has been estimated in the range of 0.2–3.2 million ha for tidal marshes, 8.3–25.4 million ha for seagrasses and 9–13 million ha for mangroves, which could draw down an additional 841 (621–1,064) Tg CO2e per year by 2030, collectively amounting to ~3% of global emissions (based on 2019 and 2020 global annual fossil fuel emissions). Mangrove protection and/or restoration could provide the greatest carbon-related benefits, but better understanding of other BCEs is needed. BCE destruction is unlikely to stop fully, and not all losses can be restored. However, engineering and planning for coastal protection offer opportunities for protection and restoration, especially through valuing co-benefits. BCE prioritization is potentially a cost-effective and scalable natural climate solution, but there are still barriers to overcome before blue carbon project adoption will become widespread