Measuring mangrove carbon loss and gain in deltas

Abstract

Demand for mangrove forest resources has led to a steady decline in mangrove area over the past century. Land conversions in the form of agriculture, aquaculture and urbanization account for much of the deforestation of mangrove wetlands. However, natural processes at the transition zone between land and ocean can also rapidly change mangrove spread. In this study, we applied a robust field-based carbon inventory and new structural and temporal remote sensing techniques to quantify the magnitude and change of mangrove carbon stocks in major deltas across Africa and Asia. From 2000-2016, approximately 1.6% (12 270 ha) of the total mangrove area within these deltas disappeared, primarily through erosion and conversion to agriculture. However, the rapid expansion of mangroves in some regions during this same period resulted in new forests that were taller and more carbon-dense than the deforested areas. Because of the rapid vertical growth rates and horizontal expansion, new mangrove forests were able to offset the total carbon losses of 5 332 843 Mg C by 44%. Each hectare of new mangrove forest accounted for ∼84% to ∼160% of the aboveground carbon for each hectare of mangrove forest lost, regardless of the net change in mangrove area. Our study highlights the significance of the natural dynamics of erosion and sedimentation on carbon loss and sequestration potential for mangroves over time. Areas of naturally regenerating mangroves will have a much larger carbon sequestration potential if the rate of mangrove deforestation of taller forests is curbed.

Global declines in human‐driven mangrove loss

“…We selected a change threshold of −0.2 based on Lagomasino et al. (2019) that occurred within the Global Mangrove Forests Dataset (GMFD; Giri et al., 2011) to be considered a permanent loss of mangroves. In order to determine the accleration or deceleration of mangrove loss, we repeated this analysis using temporal subsets: 2000–2005, 2005–2010, and 2010–2016.…”

“…Therefore, spatially explicit information is needed to identify the prevalence and variety of anthropogenic stressors driving forest vulnerability at local scales. Gains in mangrove area have also become increasingly prevalent in some regions, helping to offset losses (Hakimdavar et al., 2020; Lagomasino et al., 2019), though identifying the causes of loss can address continued threats necessary to move forward toward zero net loss in global mangroves.…”

Widespread mangrove damage resulting from the 2017 Atlantic mega hurricane season

“…We quantified annual mangrove damage and mortality (2009-2017) using the NDVI greenness index derived from two satellite instruments: Landsat 7 Enhanced Thematic Mapper+ and Landsat 8 Operational Land Imager using Google Earth Engine following a modified approach from Lagomasino et al [32]. We calculated the response of mangroves to a given hurricane season by first calculating a prehurricane season reference NDVI value for each pixel as a median from the end of the previous hurricane season (November 1) to the beginning of the given hurricane season (June 1).…”

Evaluating Combinations of Sentinel-2 Data and Machine-Learning Algorithms for Mangrove Mapping in West Africa

“…However, studies monitoring mangroves in Africa are unevenly distributed in space and time. Several studies documented mangrove extent or changes across Africa [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], but primarily focusing on a few countries, such as Gambia, Guinea-Bissau, Guinea, Mauritania, Mozambique, Madagascar, Nigeria, Senegal, Sierra Leone, South Africa, and Tanzania. Moreover, most studies do not cover a temporal span suitable for longer-term consistent monitoring, such as those useful for tracking the sustainable development goals (SDG) adopted by the United Nations, especially Goal 15 ('Life on Land') indicator 15.1.1 for quantifying "forest area as a proportion of total land area".…”