評估非生物因子及玉山箭竹對於臺灣冷杉林植群組成之影響

Abiotic Factors and Yushania Influences on Abies Forest Composition in Taiwan

在臺灣高海拔山區，臺灣冷杉（Abies kawakamii（Hayata）Ito）為優勢構成的森林分布於海拔三千公尺以上的山地。其植群組成資料來源為國家植群多樣性調查與製圖計畫資料庫（簡稱國家植群資料庫），而環境因子則是使用WorldClim及國家植群資料庫。我們使用非計量多元尺度法（non-metric multidimensional scaling）來鑑別臺灣冷杉林的物種組成，並使用結構方程模式來確認臺灣冷杉林與環境因子及玉山箭竹間的複雜因果關係。分析的結果顯示臺灣冷杉植群的組成受到棲地的岩石地比例、熱荷指數（heat load index）、溫量指數（warmth index）以及冬、夏季的降水等影響。結構方程模式之結果則證實了溫量指數及冬季降水是決定潛在變量—氣候的主要驅動變數，而氣候則是影響臺灣冷杉林上層植物組成的顯著的因子。玉山箭竹的相對頻度則是對冠層組成具有部分影響。對於地被植群來說，玉山箭竹的相對頻度則具有高度相關且明顯的影響，而其頻度本身則是受到土壤含石率及冬季降水的影響。此外，冠層植群組成對於地被具有負值且不顯著的相關係數，這可能肇因於臺灣高海拔地區破碎及異質性棲地的影響。

Abies kawakamii forests are generally distributed above 3,000 m in Taiwanese high mountains. The community data used in our analysis were derived from the database of the National Vegetation Diversity Inventory and Mapping Project of Taiwan (NVDIMP), and environmental data were obtained from the WorldClim and NVDIMP databases. We used non-metric multidimensional scaling (NMDS) to identify vegetation composition of Abies communities and the structural equation models (SEMs) were used to examine the complex relationships between environmental factors and vegetation composition. The results of ordination showed the most important factors determining species composition of Abies forests involved habitat rockiness, heat load index, warmth index and summer and winter. SEM results approved the warmth index and winter precipitation were the main drivers determining the latent variable—climate, which significantly affect the overstory composition of Abies communities. The relative frequency of Yushania niitakayamensis also had a minor effect on the overstory. However, the relative frequency of Yushania had strong and significant effects on the understory flora and it was also strongly correlated with rock ratio and winter precipitation. Moreover, the overstory displayed a negative but insignificant coefficient on the understory composition, and this might be attributed to the fragile and high heterogeneous habitat in Taiwanese high mountain areas.