Mangrove forest distributions and dynamics (1975-2005) of the tsunami-affected region of Asia

• Published in: Journal of biogeography Vol. 35; no. 3; pp. 519 - 528
• Main Authors: Giri, C., Zhu, Z., Tieszen, L. L., Singh, A., Gillette, S., Kelmelis, J. A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.03.2008; Blackwell Publishing Ltd; Blackwell Publishing; Blackwell
• Subjects: Agriculture; Animal and plant ecology; Animal, plant and microbial ecology; Aquaculture; Artificial satellites; Biogeography; Biological and medical sciences; Change analysis; Deforestation; Forestry; Fundamental and applied biological sciences. Psychology; General aspects; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; image analysis; image processing; Indian Ocean tsunami; Landsat; Mangrove forests; Remote sensing; Sustainable agriculture; Synecology; Tsunamis; Indian Ocean; Asia; Deforestation; Change analysis; image processing; Space remote sensing; Indian Ocean tsunami; Landsat; Biogeography; Tsunami; Tropical forest; Vegetation dynamics; Image; mangrove forests
• ISSN: 0305-0270; 1365-2699
• DOI: 10.1111/j.1365-2699.2007.01806.x

We aimed to estimate the present extent of tsunami-affected mangrove forests and determine the rates and causes of deforestation from 1975 to 2005. Our study region covers the tsunami-affected coastal areas of Indonesia, Malaysia, Thailand, Burma (Myanmar), Bangladesh, India and Sri Lanka in Asia. We interpreted time-series Landsat data using a hybrid supervised and unsupervised classification approach. Landsat data were geometrically corrected to an accuracy of plus-or-minus half a pixel, an accuracy necessary for change analysis. Each image was normalized for solar irradiance by converting digital number values to the top-of-the atmosphere reflectance. Ground truth data and existing maps and data bases were used to select training samples and also for iterative labelling. We used a post-classification change detection approach. Results were validated with the help of local experts and/or high-resolution commercial satellite data. The region lost 12% of its mangrove forests from 1975 to 2005, to a present extent of c. 1,670,000 ha. Rates and causes of deforestation varied both spatially and temporally. Annual deforestation was highest in Burma (c. 1%) and lowest in Sri Lanka (0.1%). In contrast, mangrove forests in India and Bangladesh remained unchanged or gained a small percentage. Net deforestation peaked at 137,000 ha during 1990-2000, increasing from 97,000 ha during 1975-90, and declining to 14,000 ha during 2000-05. The major causes of deforestation were agricultural expansion (81%), aquaculture (12%) and urban development (2%). We assessed and monitored mangrove forests in the tsunami-affected region of Asia using the historical archive of Landsat data. We also measured the rates of change and determined possible causes. The results of our study can be used to better understand the role of mangrove forests in saving lives and property from natural disasters such as the Indian Ocean tsunami, and to identify possible areas for conservation, restoration and rehabilitation.