Root–soil load transfer mechanisms upon tree overturning: a closer look on the soil stress state evolution and root strength mobilisation

Understanding the anchorage of a complex root system architecture (RSA) in soil upon tree over-turning is vital to evaluate tree stability under lateral loads. Empirical correlations between root anchorage capacity and root morphological traits have been established, but the role of soil in these correlations has been ignored. This study developed and validated a three-dimensional fi-nite-element model and then used it to investigate the underlying mechanisms of root–soil load transfer mechanisms in terms of the evolution of soil stress states and root strength mobilisation during overturning. Two root traits—radial distance and embedded depth— influenced root anchor-age capacity remarkably. The pattern of soil stress state evolution near taproots and laterals was remarkably different. Roots that displaced in the direction more aligned with the soil’s major principal stress were more effective to mobilise their strength to resist against overturning. The failure envelope defined by the normalised peak moment capacity in the x- and y-direction of the asymmetric RSA was elliptic, displaying anisotropic overturning under combined load conditions.