Rapid Estimation of Mangrove Area and Carbon Sequestration in Land Subsidence Regions of Coastal Taiwan

Mangroves represent a key component of coastal ecosystems. From 1897 to 2024, Taiwan’s southwest coast experienced marked climatic shifts, including a 2.0 °C increase in average annual temperature and a 56.5 mm reduction in annual rainfall. Among 18 coastal towns in western Taiwan, Taixi Township in Yunlin County exhibited a cumulative land subsidence of −283.0 cm from 1975 to 2023. The grey/white mangrove (Avicennia marina) in regions with severe subsidence exhibited slow growth or mortality. In the present study, mangrove area (MA) was estimated using a quadratic polynomial trend equation. The total MA at Tougang Ditch was −0.0084(t − 21.0)2 + 2.8, with t = 21.0 in 1995, and that at Budai Lagoon was −0.0468(t − 12.3)2 + 26.1, with t = 12.3 in 1986, supported by high coefficients of determination (R² > 0.85), respectively. SPOT-6 satellite images from February 22, 2025, were used to assess the coastal landscapes of Chiayi County and Tainan City. The total MA and windbreak forest area were 281.9 and 896.3 ha, respectively. The long-term assessment method introduced in this study may help predict mangrove health and carbon sink stocks and refine carbon sequestration estimates in subsidence or sea-level-rise regions.