根系结构不同, 其固持土体的能力存在很大差异。利用分形理论对不同根系结构稳定土体的能力进行了量化比较, 结果表明: (1) 长江上游暗针叶林生态系统中主要树种根系都表现出了较为明显的分形结构特征, 高山柳(Salix sp. ) 的根系结构最复杂, 具有多层次细微分枝结构, 分形维数最大, 达1.735675, 冬瓜杨(Populus purdomii) 次之, 为1.60166, 峨眉冷杉(A biesfabri) 分枝结构简单, 以侧行主根为主, 分形维数仅为1.44938, 并且根系的分形维数随着其年龄的增长而增大。(2) 根系结构与稳定土体的能力明显相关, 根系直径或树干基径与根系抗拉阻力受环境条件的影响, 关系较为复杂; 而根系分形维数更能揭示根系的结构与发育动态, 根系分形维数与抗拉阻力的对数呈比较稳定的指数函数关系。(3) 峨眉冷杉根系结构简单, 垂直根系较少, 且分布层次较浅, 在冰碛物环境中可以通过在岩石中迂回缠绕而从较大范围内将岩石、土壤等压在其下, 但结构较为散乱; 而冬瓜杨以垂直分布为主, 分布层次较深, 毛根很发达, 土壤颗粒间的粘结程度较好, 二者结合配置将有助于改良土壤结构, 防治水土流失, 尤其是超强度水土流失的发生。

The stability of soil-body varied with different roots structures. Based on the fractal theory, the soilps feature of stability dominated by different roots with various structures has been quantified. Some conclusions have been drawn as following: (1)The structure root system ofmajor trees show s a generally distinctive fractal feature in such dark coniferous ecosystem at the upper reach of Yangtze Rive. The structure of Salixsp. root system is the most complex, and it hasmulti-grade structure with m icro-branches, thus with the biggest fractal dimension of 1.735675. Populuspurdomii is the second one, and it is 1.60166. The root system of A bies f abri branches relatively simple with fewerfibrous roots. Its lateral rootsmainly distribute at horizontal level. The fractal dimension of it is 1.44938. In common, the fractal dimensions increase with their ages. (2) The structure of root system has distinct effect on soil-body stability. How ever, the relationship between the average root diameter or the base stem diameter and its corresponding pull2resistance is comp licated by some environmental components. The index of fractal dimension (FD) is well suitable to describe the structure of root system as well as its developing dynamics. An exponential function has been founded on FD and pullresistance of root system. (3) A biesfabrihas simple root system structure with few vertical roots and many horizontal roots in shallow soil layer. But it can consolidate stock and soils with in its tension sphere by twining force. While Populus purdomii dives deep in soils with plenty of fibrous roots, which strengthen the adhesive of soil granular. If these two species are composed together, the physical conditions of soil environment could be improved, and soil and water losses, especially violent one could be controlled effectively.