Regeneration by sprouting in secondary forests is a necessary technique not only for the utilization of forest resources, but also for maintaining forest health by regrowth and avoiding slope instability caused by over-sized aboveground biomass. The strength of soil reinforcement by roots generally decreases during the tree death process in deforestation, such as clear-cutting, whereas root system strength temporarily decreases in trees that regenerate sprouting after cutting. However, quantitative evaluation of decreasing soil reinforcement by roots and slope stability has not been conducted during regeneration. In this study, we evaluated changes in the number of roots and root distribution up to 3 years after cutting in the regeneration process of Quercus serrata, a major dominant species of secondary forests in warm and cool temperate zones in Japan. We also estimated soil reinforcement by roots: additional cohesion from roots using the root bundle model, and slope stability based on a factor of safety by dividing the effect of the tree root system into vertical and horizontal cohesion with soil physical properties. After cutting at the height of approximately 0.2 m, the aboveground sprouting branches immediately regenerated, whereas the belowground root system gradually decayed. The additional cohesion from roots in trees before cutting was calculated as 34.6 kPa, whereas it decreased significantly to 21.7 kPa in living stumps 3 years after cutting. The value for the factor of safety with a saturated soil thickness of 0.7 m was calculated as 1.20 in soil under trees before cutting, whereas it decreased significantly to 1.11 in soil under living stumps in the 3 years after cutting. The safety factor's value to 0.99 in soil under dead stumps, which did not regenerate sprouts within 3 years after cutting. We concluded that the probability of slope failure was significantly greater in the dead stumps than in the living stumps and could vary depending on the dynamics of above- and below-ground parts, including fine roots.

在次生林中发芽再生不仅是利用森林资源的一种必要技术，而且对于通过再生来维持森林健康和避免因地上生物量过大而引起的边坡不稳定性而言，也是一项必要的技术。在砍伐森林等砍伐森林的树木死亡过程中，通过根部加固土壤的强度通常会降低，而在砍伐后重新萌芽的树木中，根系强度会暂时降低。然而，在再生过程中尚未进行通过根和边坡稳定性降低土壤加固作用的定量评估。在这项研究中，我们评估了锯齿栎（Quercus serrata）再生过程结束后长达3年的根数和根系分布的变化。是日本暖温带温带地区次生林的主要优势种。我们还估算了通过根部进行的土壤加固：使用根束模型从根部获得附加的内聚力，以及通过将树根系统的影响分为具有土壤物理特性的垂直和水平内聚力，基于安全因素的边坡稳定性。在约0.2 m的高度切割后，地上的发芽分支立即再生，而地下的根系逐渐腐烂。砍伐前树木根部的附加内聚力经计算为34.6 kPa，而砍伐后3年的活树桩中的附着力显着降低至21.7 kPa。砍伐前树木下土壤中饱和土壤厚度为0.7 m时的安全系数值为1.20，而在砍伐后的三年中，在活残树桩下的土壤中其显着下降至1.11。在死树桩下的土壤中，安全系数的值为0.99，该土壤在切开后的3年内不会再生。我们得出的结论是，死树桩的边坡破坏概率要比活树桩的概率大得多，并且可能随地上和地下部分（包括细根）的变化而变化。