| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 97 === Regions or some environmental factors associated with altitude may influence the distribution of vegetations in Taiwan. The purposes of this study were not only to prove the effects of altitude on vegetation differentiation but to identify whether there are regional effects on vegetation compositions and altitudinal distribution. Cluster analysis shows that no significant regional differentiation of vegetations above alt. 2500 m, while shows similar regional differentiation patterns among altitudinal bands below alt. 2500 m. Watersheds with similar species composition are grouped. Three vegetation regions along the latitudinal gradient are identified: the north, central (including west subregion and east subregion) and south (including southwest subregion and southeast subregion) regions. Because the south region belongs to the tropical zone, while the north region belongs to subtropical one, different temperature conditions cause the diverse vegetation composition. Furthermore, the winter rainfall caused by the winter northeast monsoon in the north region and the southeast subregion also results in regional differentiation of vegetation. After examining the vegetation altitudinal distributions for each region, six vegetation types are identified. In the ascending order of altitude, these vegetation types are the Ficus-Machilus, Machilus-Castanopsis, Quecus, Tsuga-Chamaecyparis, Abies-Tsuga and Abies-Juniperus bands. The Ficus-Machilus band occurs in all but the north region. Our results show that the altitudinal distribution of three vegetation bands at low to mid altitudes, the Ficus-Machilus, Machilus-Castanopsis, Quecus and Tsuga-Chamaecyparis bands, is lower in the north region and the southeast subregion than in others. The winter monsoon is considered as the most important cause of the lower altitude of vegetation types in the north and southeast.
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