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

Mangrove ecosystems along Taiwan’s southwest coast have been increasingly stressed by climate change, subsidence, and sea level rise. Between 1897 and 2024, the mean annual temperature rose by 2.0 °C, and rainfall declined by 56.5 mm. Severe subsidence occurred in Taixi Township, Yunlin County (−283.0 cm, 1975–2023), where the gray/white mangrove (Avicennia marina) exhibited reduced growth and mortality. Long-term mangrove area (MA) was reconstructed using quadratic polynomials: Tougang Ditch, MATG(t) = −0.0084(t − 21.0)2 + 2.8 peaking in 1995 (R2 = 0.7274), and Budai Lagoon, MABD(t) = −0.0468(t − 12.3)2 + 26.1 peaking in 1986 (R2 = 0.782). Both sites yielded moderate fits indicating partial but less reliable reconstruction. In contrast, Jishui Estuary subsites displayed distinct maxima with stronger fits (R2 > 0.85): JS-C, MAJS-C(t) = −0.0201(t − 14.3)2 + 7.0 peaking in 1996; JS-D, MAJS-D(t) = −0.0093(t − 15.8)2 + 2.2 peaking in 1998; and JS-G, and MAJS-G(t) = −0.0077(t − 11.6)2 + 4.3 peaking in 1994. SPOT-6 satellite imagery (22 February 2025) identified 281.9 ha of mangrove and windbreak forests in Chiayi County and 896.3 ha in Tainan City. By integrating climate records, subsidence data, sea level rise, polynomial modeling, and satellite observations, this study provides a robust framework for anticipating mangrove trajectories, assessing carbon sink potential, and refining carbon credit estimates in vulnerable coastal landscapes.