| Summary: | 碩士 === 靜宜大學 === 生態學研究所 === 93 === Abstract
This study was conducted in Toukoshan (Da-Keng) which is located in the east side of Taichung basin and is classified as part of the overthrust belt geologically. Because of predominating gravel proportion in the upper part of Toukoshan, this area is characterized by steep cliff and jagged ridge. Previous studies have showed that the major characteristics of the vegetation in Da-Keng are the dominance of deciduous species and the formation of a deciduous forest in a lowland area in Taiwan. This phenomenon could be related to the environmental factors, such as high proportion of gravel, frequency of earthquake, frequency of fire, frequency of collapse, and seasonality. Therefore, this research aimed to understand: (1) what is the vegetation composition in Toukoshan; (2) to what degree can the environmental factors (altitude, aspect, slope, rock proportion, and degree of collapse) affect the composition of vegetation in Toukoshan; (3) what is the relationship between the distribution of deciduous species and environmental factors.
There were 1,790 individuals (≥ 1 cm) belonging to 95 species, 78 genera and 38 families recorded in Da-Keng Trail No. 2. Based on the defoliation characteristics, the plants can divide into 3 different groups: deciduous trees (30 species, 31.6%), evergreen trees (54 species, 56.8%), and semi-deciduous trees (11 species, 11.6%). Evergreen tree was the group with the highest proportion, while deciduous tree also accounts for 1/3 species in Da-Keng. According to the basal area, dominant species were Cyclobalanopsis globosa, Zelkova serrata, Cyclobalanopsis glauca, Sapindus mukorossii, and Sapium discolor. In total, they accounted for 54.02 % basal area in this transect. As for the density, the dominant species were Cyclobalanopsis globosa, Gardenia jasminoides, Psychotria rubra, Cinnamomum osmophloeum, and Cyclobalanopsis glauca. Overall, the top 5 IVI (important value index) species accounted for 31.2% IVI in this area, including Cyclobalanopsis globosa (semi-deciduous), Zelkova serrata (deciduous), Cyclobalanopsis glauca (semi-deciduous), Sapindus mukorossii (deciduous), and Cinnamomum osmophloeum (evergreen).
The structure of the forest is discontinuous. It can approximately be divided into three levels, including canopy, sub-canopy, and shrub. The under-ground level is not apparent. Though out the diameter-analysis the woody plants can simply be divided into J shape, Reverse J shape, Slight bell shape, Salient shape and Wave shape.
The results of Chi-square test revealed that the distribution patterns of plants were significantly affected by environmental factors. There are 30 species significant in the elevation chi-square test, 14 species significant in the slope chi-square test, 27 species significant in the aspect chi-square test, 17 species significant in the collapse chi-square test, and 15 species significant in the rock proportion chi-square test. The results of Chi-square test in the distribution of deciduous plants were significant in elevation, slope, and the ratio of rocks. Deciduous trees preferred relative low elevation, evergreen trees preferred relative high elevation, while the semi-deciduous trees preferred relative mid-high elevation. The distribution of deciduous trees were not obviously related to slope degree, evergreen trees were aggregated in 2nd and 5th slope-levels. The semi-deciduous trees were aggregated in 3rd and 4th slope-levels. According to Yang （2002）, after earthquake, the recruits species are pioneer and deciduous trees. The reason why the degree of collapse did not have significant result in the chi-square test could be due to the in situ situation not necessary reflects the collapse history. Because this research was conducted in the ridge top, the differences of solar energy and water gradient between different slop degrees were not significant. Most of the species were located in the northwest slope.
In short, there are high proportion of deciduous individuals and species in the Trail No.2 in Da-Keng. Moreover, the distribution of deciduous trees was related to altitude, slope, and rock ratio.
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