Study On Dynamical Changes Of Mangrove Forests In Coastal Zone Of Thailand Based On Remote Sensing

Mangroves are evergreen shrubs or trees which grow in upper low-energy intertidal zone of tropical or subtropical area, and are.inundated by periodic tide.Mangroves have special morphological structure and physiological function.They have play an important role in purifying seawater, absorbing waves,protecting coasts and bank, regulating climate and protecting biological diversity. They also have important economic value and ecological service function.Thailand, which located between the Indian Ocean and the Pacific Ocean,has a long coastline with a mass of coastal wetlands. There are much of mangroves, and is one of the world’s areas with the highest density of mangroves. In history, due to excessive coastal development especially the shrimp farming, the mangroves in coastal area of Thailand had a degradation of large area. That caused many of external effects such as the decrease of fishery production, water pollution, coastal erosion, and the reduction of biodiversity.To supervise the changes of mangroves in coastal area of Thailand, this paper takes the data of Landsat TM/ETM/OLI satellite images around 1988-2016 as the main data sources, and use DEM data to mask part of not mangrove growth area. With the combination of field reconnaissance, build the interpretation signs of image. On basis of comparison of three classification methods including maximum likelihood method, neural network method and support vector machine (SVM) method, this paper selects the neural network method which has the highest overall classification accuracy to conduct a supervised classification of images. Then obtain the distribution of mangrove in coastal area of Thailand, and make a statistics of acreage of mangroves. The main research conclusion of this paper is as follows:(1)The mangroves in coastal area of Thailand experienced a process of increasing after reducing for nearly 30 years. From the year around 1988 to the year around 2016, the total area of mangroves in coastal area of Thailand is increased by 37219.22 hm2. The total area of mangroves around the year 2016 is about 227466,69 hm2, which increased by 15.96% than the year around 1988,with an average annual growth rate of 1329.26 hm2/a.(2)The mangroves in coastal area of Thailand is mainly .distributed in four.areas, which are the coast of Andaman sea, the western coast of the gulf of Thailand, the eastern coast of the gulf of Thailand and the northern coast of Bay of Bangkok. Among them, the largest mangrove area is the coast of Andaman sea, with a proportion about 75.39%-80.11%. The second is the western coast of the gulf of Thailand,with a proportion about 10.44%-13.69%. The third is the eastern coast of the gulf of Thailand, with a proportion about 5.57%-7.65%. The least is the northern coast of Bay of Bangkok, with a proportion about 2.83%-3.5%.(3)There’s different changing trend of four areas of mangroves in Thailand.There’s a trend of firstly significantly reduce then rapidly increase and finally slowly increase of the mangroves in the coastal area of Andaman sea. The mangroves in the western coast of the gulf of Thailand have a characteristics of early slowly increase and rapidly increase in the later. The mangroves in the eastern coast of the gulf of Thailand show a trend of early reduce and increase in the later. The mangroves in the northern coast of Bay of Bangkok have a trend of early reduce and continue increase in the later.(4)The area of mangroves for each province in the coastal of Thailand is significantly different. The three province of Phangnga, Satun and Krabi has an average mangrove area above 30000 hm2,which take up 52.91% of the total area of the national mangroves. The area of mangroves of -the province of Changwat Songkhla, Narathiwat, Prachuap Khiri Khan, Samut Sakhon, and Bangkok are all less than 600 hm . Bangkok has the smallest area of mangroves.(5)The change of mangroves is the result of both natural factors and human factors. The main causes of mangroves degradation including the raising development of the shrimp industry, water pollution and the expansion of the artificial construction. The main driving factors of the mangrove expansion include the attention for protection of government, the establishment of ecological conservation and the seaward expansion of river deltas.