| In this paper, area, distribution and landscape pattern of China’s mangroves arestudied based on objected-oriented and decision tree classification of Landsat imagery.During image interpretation, we found that tidal condition of satellite images play animportant role in mangrove extraction. Therefore, an inundated mangrove forest index(IMFI) was generated to distinguish the inundated mangrove forests from waterbackground. When extracting mangroves, IMFI was used to distinguish inundatedmangrove forest, so that the classification results would be more accurate. This resultwould benefit the application of remote sensing imagery in coastal wetlandsmonitoring. Guangxi was chose to study driving mechanism of mangrove changesfrom1973~2013. Based on the analysis of conversion between mangroves and otherland use types, driving mechanisms were confirmed. This would provide a s Providescientific support and decision making consult for protection, using and ecologicalrestoration of mangrove forests.The results show that:(1) There are obvious differences between the spectral curves of the inundatedmangrove forest and seawater in the reflectances of bands1(blue),2(green), and4(NIR). The IMFI was proven to be effective in detecting the extent and condition ofmangrove forests from satellite images that were captured during local high tidalperiods.(2) Total area of China’s mangrove forests in1973,1980,1990,2000,2010, and2013are48750hm2,22450hm2,20430hm2,18587hm2,20776hm2, and32077hm2,respectively. The landscape index showed that the fragmentation of mangrovelandscape has gradually increased, landscape pattern of mangrove forests is becomeuniform, and the degree of dispersion of landscape distribution has increased. (3) The temporal analysis of the areal extent of mangrove forest indicated thatmangrove forests in China decreased sharply first and increased notably later.Guangdong, including Hong Kong and Macao, has the largest area of mangroveforests; mangrove area in1973,1990,2000,2010, and2013is33234hm2,11286hm2,7630hm2,9678hm2, and16348hm2, respectively. Mangrove area in most provinceswas increased from1990, exceptted Guangxi which increased from1980.(4) Mangrove forests in national natural reserves also decreased first andincreased later. Mangroves in Shankou Mangrove Nature Reserve, Guangxi BeilunEstuary National Nature Reserve, Dongzhaigang Mangrove Nature Reserve,Zhanjiang Mangrove Nature Reserve, and Fujian Zhangjiangkou National MangroveNature Reserve were recovered during the same year of reserve establishment.Although Futian mangrove nature reserve was established in1984, mangroves therewere recovered since year of2000. Mangrove in Mai Po mangrove reserve is bestprotected.(5) During1973to2013, in Guangxi province, conversion between mangroveforests and other land cover types was drastic. From1973to1990, areas of mangroveforests were reclaimed to crop lands; during1990to2013, reforestation of mangroveshas caused mangrove recovery; area decrease from2000~2010were mainlyinfluenced by natural factors. Reclamation and natural factors caused mangroveforests losses; protection and reforestation efforts contributed to mangrove forestrestoration.(6) The study results indicate that the fragmentation of mangrove forests wasmainly caused by three factors. First, local people have walked in mangrove forestsand destroyed many seedlings and young trees, breaking the twigs, and damaging theroots, resulting in fragmentation. Second, many mangrove trees were cut down toform an artificial water ways parallel to the bunds, so that the boats can anchoreverywhere along the bunds. Third, direct emission of pollution from production andliving caused mangrove fragmentation. Mangrove moving seaward was also causedby three factors. First, landward mangrove forests were reclaimed and converted intobuilt-up lands. Second, the built-up lands limited the area for landward migration. Third, the increasing built-up lands brought heavy population and pollution pressuresto near-land mangrove forests. |
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