Comparison of Vertical Distribution of Root Weight between Hinoki Cypress (Camaecyparis obtusa) and Oak (Quercuss crispula)

扁柏种植园中扁柏和柞树根重垂直分布的比较人们常说，扁柏和日本雪松等针叶树种的浅根特性导致相对年轻的人工林在遇到特大暴雨时倒塌。为了检验这一点，我们比较了扁柏（Camaeraparis obtusa）和橡树（Quercus crispula）之间的垂直根分布格局。在一个48年生的扁柏种植园中，选择了一个胸径14.28cm，高11.9m的扁柏个体和一个胸径12.8cm，高12.8m的栎属个体。在每株样树下挖沟，沟宽20cm，长100cm，深60cm，从树干基部向三个方向设置，上坡、下坡和侧向。将沟渠进一步细分为10厘米深和20厘米宽的土壤块。两种样木根重在坡面上的水平分布格局不同。栎样木向上根系发达，而扁柏样木向下根系发达。根重密度的垂直分布随土层深度的增加呈指数下降。根重密度的下降速率在两个样木之间没有统计学差异。通过对任意土层深度的指数方程积分，计算出单根重。从土壤表面到30cm深度的单根重量分别占总根重量的89%和94%。两种样木表现出相似的浅根行为。

Comparison of Vertical Distribution of Root Weight between Hinoki Cypress (Camaecyparis obtusa) and Oak(Quercuss crispula) Individuals Growing in a Hinoki Plantation. It is often said that the shallow rooted characteristic of coniferous tree species such as Hinoki cypress and Japanese cedar leads to the collapse of relatively-young artificial forests when they meet with extraordinary heavy rain. To examine this, we compared the vertical root distribution pattern between Hinoki Cypress (Camaecyparis obtusa) and an oak (Quercuss crispula). In a 48-year-old Hinoki plantation, a Hinoki individual (DBH : 14.28cm, H : 11.9m) and an oak individual (DBH : 12.8cm, H : 12.8m) invaded there were selected. Under each sample tree, a trench was dug of 20cm wide, 100cm long, and 60cm deep, settled for the three directions from stem base, i.e., up-slope, down-slope, and side-ward. The trench was further sub-divided into soil blocks of 10cm deep and 20cm wide. The horizontal distribution pattern of root weight on slope was different by the two sample trees. The oak sample tree developed much root in up-slope direction but the Hinoki one in down-slope direction. The vertical distribution of root weight density decreased exponentially with soil depth. The decreasing rate of root weight density was not different statistically between the two sample trees. The individual root weight was calculated by integration of the exponential equations for the arbitrary soil depth. The individual root weight from soil surface to 30cm depth formed 89% and 94% of total root weight for the oak and Hinoki, respectively. The two sample trees showed similarly the shallow rooted behaviour.