| Summary: | 碩士 === 國立臺灣大學 === 地理學研究所 === 87 === The distribution of Kandelia candel in the estuary of the Tanshui River is concentrated mainly in three areas, Chuwei, Kuandu, and Watzewei. Since 1978, the Kuandu vegetation has changed significantly. The habitat area of Kandelia has increased rapidly and the coverage of both Cyperus and Phragmites has decreased. In order to manage the “Kuandu Nature Reserve Area” properly, the vegetation change of the Kuandu area needs to be studied. The purpose of this study is to investigate the trends and causes of the vegetation changes in the Kuandu area.
A series of aerial photos from 1978 to 1997 are used to interpret the distribution of vegetation types. GIS and image processing are used to detect vegetation changes among three time intervals, 1978, 1986 and 1997. Field elevation survey and soil sampling are carried out to analyze the relationship between each vegetation type and its habitat environment factors.
The temporal vegetation changes reveal that the marsh habitat, dominated by Phragmites and Cyperus has been gradually changed into the swamp habitat, dominated by Kandelia and Phragmites. The spatial distribution of the Kandelia tends to spread along the wetland creeks and the Keelung River. Vegetation change detection shows that the mud flat is closely related to the expansion of Kandelia. The results of elevation survey show that the average elevation of Kuandu area is increased. The elevation range is 0.2-0.3m(n=205) for the Kandelia, and 0.3-1.4m(n=105) for the Phragmites. The ANOVA test shows that the habitat elevation range of the Kandelia is significantly different from that of the Phragmites(α=0.05). Soil electrical conductivity analysis indicates that salinity of Phragmites habitats is lower than that of Kandelia. The human factors, especially human-induced land subsidence, might have significantly contributed to the vegetation changes in the Kuandu area. Base on this reason, it is predicted that the distribution of Kandelia will increase continually in the Kuandu area.
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