Restoring Guinea’s mangroves for coastal resilience
The objectives of the study are to estimate the total economic value (TEV) of mangrove in Guinea.
Guinea’s coastal and marine areas—the largest in West Africa—require comprehensive policy planning and ecosystem management. The country’s continental shelf extends 300 km, covering a 47,400 km2 area dotted by inlets, tidal marshes, estuaries, and numerous offshore islands. Mangrove areas, which extend along most of the coast and up to 40 km inland, remain large and biodiverse, but have declined by more than 30 percent since the early 1980s. A 2019 survey by NASA estimates total mangrove cover at 2,076 km2, of which only 1,000 km2 can be utilized for sustainable, commercial exploitation.
Mangroves can play a potentially large role in strengthening coastal-area resilience. “Green” coastal management with mangroves is not a new concept in Guinea. Between 1993 and 1998, mangrove restoration using Rhizophora and Avicennia species was undertaken to mitigate degradation in Sangareya Bay, where 700,000 m2 of mangrove lands had previously been cleared for Kamsar port expansion. More than 400 km of mangrove bunds have been created to protect rice crops from excessive flooding, with the added benefits of reducing shoreline erosion and the need for manmade engineering structures. Today, this natural infrastructure solution is at risk from overharvesting, land clearing, and impacts from predicted sea-level rise. Exacerbating the issue is a failure to maintain dykes built decades ago and integrate climate-related concerns into coastal planning and infrastructure construction.
A recent World Bank study tested the cost-effectiveness of integrating mangroves into Guinea’s coastal management policies and strategies. The focus of the study was Guinea’s 2,700 km2 of existing mangroves, which are in varying states of degradation. The study’s twofold objectives were to (i) estimate the current economic value of mangrove areas, considering their full range of private and social benefits and (ii) use those values in cost-benefit analyses to determine the potential for reforestation and afforestation. All values were obtained from a literature survey of studies conducted in Guinea (or from data at similar locations elsewhere) and were adjusted to 2020 purchasing power parity (PPP) dollars using inflation data in Guinea and the PPP dollar conversion factor. The results were reported as a mean value per hectare and total annual value.
The study suggests how mangrove over-exploitation from direct private use could be halted. Wood from Guinea’s true mangrove species (Acrosticum aureum, Avicennia germinans, Conocarpus erectus, Laguncularia racemosa, Rhizophora harrisonii, R. mangle, and R. racemosa) is commonly used in fish smoking and salt production, as well as for household fuelwood and timber. The mean value of these direct private-use benefits is US$248 per ha, with a total estimated value of US$52 million. The 220,000 MT of mangroves currently harvested annually to meet those needs exceeds natural wood growth in the 1,000 km2 of commercially suitable area by about 70,000–140,000 MT. However, if all 2,700 km2 of mangrove lands could be made commercially suitable, annual sustainable yield would reach 210,000-410,000 MT.
The findings highlight the large, indirect private-use benefits from mangrove forests. The sustainability of Guinea’s fishery enterprises and coastal rice farms depend highly on healthy mangrove ecosystems. Based on the quantity of fish harvested and market price, the added value of mangroves to the fisheries sector is estimated at US$1,119 per ha, with a total value of US$232 million per year. Coastal rice cultivation has an estimated mean value of US$7,896 per ha, with a total value of US$616 million per year. Located adjacent to mangrove bunds, coastal rice farms account for 23 percent of national rice production, providing livelihoods for more than 50,000 rice farmers, the majority of whom are women. Coastal rice farming is considered an alternate private use since cultivation occurs on lands once devoted to mangrove plantations.
Key co-benefits to society were also assessed. The study mainly focused on carbon sequestration, protection from coastal flooding, and water purification. The mean annual and total estimated values of carbon sequestered, at US$221 per ha and US$49 million per year, were based on allometric studies that assessed the amount of carbon content in mangroves and the price of carbon. The respective values for flood protection (US$1,120 per ha and US$232 million per year) and water purification (US$151–504 per ha and US$31–105 million per year) were based on outside studies since none could be found in Guinea. In addition, the social non-use value of protecting biodiversity in two habitats along the western coast was conservatively estimated at US$911–1,651 per ha or US$189–343 million per year, based on a willingness-to-pay approach.
The results make a strong case for investing in Guinea’s mangroves. The valuation of benefits from private indirect use, social use, and social non-use far outweighs that of direct private-use benefits, suggesting that incentives discouraging over-exploitation would lead to net social benefits. The mean cost of planting is about US$968 per ha, with an annual maintenance cost of US$72 per ha. Assuming annual benefits will accrue 10 years after planting, the net present value (NPV) of direct private-use benefits over a 20-year period would total US$1,357 per ha, with a benefit-cost ratio of 1.4. Including the indirect private-use benefits from fisheries increases the NPV to US$18,503 per ha, with a benefit-cost ratio of 19; while factoring in the social-use values raises the NPV to US$38,333 per ha, with a benefit-cost ratio of 39. These figures suggest that substantial benefits may result from large-scale investments in restoring or reforesting lands with mangroves. However, it should be noted that given the large returns from coastal rice farming for ensuring food security, returning mangrove lands cleared for rice cultivation over decades back to mangroves may not be economically feasible.
For more on the benefits of mangrove afforestation and restoration programs in Guinea, please see Link to full report on Guinea.
If you’re interested in similar research on Ghana, please see Managing with Mangroves: Cost-Effective Coastline Protection for Ghana at here.
We gratefully acknowledge financial support from World Bank’s WAVES and PROBLUE Trust Fund. We are grateful to Ms. Norma Adams for her help in writing the blog.
Authors: Subhendu Roy, Susmita Dasgupta and Juan Jose Miranda