臺灣西海岸木賊葉木麻黃之根系型態與力學性質

ROOT SYSTEM MORPHOLOGY AND MECHANICAL PROPERTIES OF CASUARINA EQUISETIFOLIA IN THE WEST COAST OF TAIWAN

李嶸泰(Jung-Tai Lee) ； 蔡順明(Shuen-Ming Tsai) ； 林中鴻(Chung-Hung Lin)

《中華林學季刊》 49卷3期 (2016/09) Pp. 229-244

摘要

木賊葉木麻黃(Casuarina equisetifolia Forst., Australian pine)為臺灣海岸防風林之主要造林樹種。臺灣西海岸夏季盛行西南季風，而冬季盛行東北季風。本研究旨在以全根挖掘法及力學試驗法調查及測定臺西海岸8年生木賊葉木麻黃林分林緣木和林內木之根系形態及力學性質。研究結果顯示，木賊葉木麻黃之根系屬於垂直與水平(VH)型。林緣木之根系發育朝向東北和西南方，與季風方向一致，而林內木之根系則向南發育。林緣木側根之平均總根長、根數及乾重均顯著大於林內木者。林內木之平均主根長度和樹高顯著高於林緣木者。林內木之平均最大拉拔抗力顯著高於林緣木之平均最大拉拔抗力。根系之最大拉拔抗力與主根深度呈線性正相關。林緣木和林內木單根之最大抗剪力隨根徑之增加而增加，呈冪函數正相關，反之其單根之抗剪強度隨根徑之增加而下降，呈對數函數負相關，而林緣木單根之最大抗剪力與抗剪強度均顯著高於林內木者。林緣木和林內木單根之最大抗拉力隨根徑之增加而增加，呈冪函數正相關，而其單根之抗拉強度隨根徑之增加而下降，呈對數函數負相關，且林內木單根之最大抗拉力與抗拉強度均顯著高於林緣木者。本研究證實，風會影響木賊葉木麻黃根系之分布與型態及其力學性質，建議將此一樹種用於防風林之第二線造林樹種。

關鍵字

木賊葉木麻黃 ； 拉拔抗力 ； 根系型態 ； 抗剪強度 ； 抗拉強度 ； 風

並列摘要

Australian pine (Casuarina equisetifolia Forst.) is the main reforestation species of coastal windbreaks in Taiwan. Winds in the west coast of Taiwan are dominated by southwest monsoon in summer and northeast monsoon in winter. This study aimed to investigate the root system morphology, and determine the mechanical properties of edge and inner trees in 8-year-old Australian pine stands by total root excavation and mechanical tests. The results revealed that root system morphology of Australian pine belonged to the VH-type. The root systems of edge trees developed towards northeast and southwest, which coincided with the monsoon direction. However, root systems of inner trees developed southward. Average total length, number, and dry biomass of lateral root of edge trees were significantly higher than the inner trees. The tap root length and height of inner trees were significantly higher than the edge trees. The maximum pullout resistance of inner trees was significantly higher than that of edge trees. Regression analysis showed the linear positive correlation between the maximum pullout resistance and the depth of tap root. The maximum root shear force increased with increasing root diameter in accordance with a positive power function correlation. Conversely, root shear strength decreased with increasing root diameter in accordance with a function of negative logarithmic correlation. The root shear force and shear strength of edge trees were significantly higher than the inner trees. The maximum root tensile resistance increased with increasing root diameter in accordance with a positive power function correlation, whereas the root tensile strength decreased with increasing root diameter in accordance with negative logarithmic function correlation. The maximum root tensile resistance and tensile strength of inner trees were significantly higher than the edge trees. This study demonstrated that wind can affect root system distribution and morphology as well as its mechanical properties. Thus, it is suggested that this species can be used as second line reforestation species in windbreak forest.

並列關鍵字

Casuarina equisetifolia ； Pullout resistance ； Root system morphology ； Shear strength ； Tensile strength ； Wind