Although the effects of different vegetation cover on soil reinforcement due to their roots have been addressed in the literature, there remains a lack of assessment and comparison of root biomechanical properties of hardwood and softwood plantations for similar site conditions. To address this gap, two adjacent hillslopes with similar site conditions but different forest plantations, a Picea abies (softwood) and a Fraxinus excelsior (hardwood), were selected to assess and compare their effectiveness in protecting sloping soils. The profile trench method was used to obtain root distribution from both upslope and downslope sides of tree samples and on each side at two horizontal distances from the tree stems. Root tensile strength of live root samples was measured using a standard Instron Universal Testing Machine. A modified Wu and Waldron root reinforcement model was used to calculate root cohesion for the two plantations. The root tensile strength for was significantly greater for softwood than for hardwood trees (19.31 ± 2.64 vs 16.98 ± 1.01 MPa). Interestingly, the number of roots, root area ratio values, and the root tensile strength of the two species did not significantly differ between the upslope and downslope sides of trees. The results also showed a higher root cohesion for the softwood than the hardwood species (1.56 ± 0.34 vs 1.03 ± 0.21 kPa). In addition, softwood trees extended their contribution to soil protection to a larger horizontal distance compared with hardwood. However, our findings generally revealed that the values of root cohesion of both studied plantations were surprisingly lower than those found in earlier reports.

中文翻译：

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Picea abies 和 Fraxinus excelsior 人工林的根如何促进土壤强度和斜坡稳定性：来自伊朗希尔卡尼亚森林研究案例的证据

尽管文献中已经讨论了不同植被覆盖对其根系土壤加固的影响，但仍然缺乏对相似场地条件下硬木和软木人工林根系生物力学特性的评估和比较。为了弥补这一差距，我们选择了两个具有相似场地条件但不同森林种植园的相邻山坡，即冷杉（软木）和白蜡（硬木），以评估和比较它们在保护倾斜土壤方面的有效性。剖面沟法用于从树木样本的上坡和下坡两侧以及距树干两个水平距离处的每一侧获得根分布。使用标准英斯特朗万能试验机测量活根样品的根抗拉强度。修改后的 Wu 和 Waldron 根强化模型用于计算两个种植园的根系凝聚力。软木的根部拉伸强度明显高于硬木树（19.31 ± 2.64 对 16.98 ± 1.01 MPa）。有趣的是，树的上坡和下坡两侧的根数、根面积比值和根抗拉强度没有显着差异。结果还显示软木的根系内聚力高于硬木树种（1.56 ± 0.34 vs 1.03 ± 0.21 kPa）。此外，与硬木相比，针叶树对土壤保护的贡献扩大到更大的水平距离。然而，我们的研究结果普遍表明，两个研究种植园的根系凝聚力值都出人意料地低于早期报告中发现的值。