Quantifying the spatio-temporal mechanical root reinforcement of the pioneer species Betula pendula: experimental investigations and modelling for a case study in Western Norway

Protection forests have gained recognition as a sustainable measure for preventing shallow landslide triggering, as trees can enhance slope stability through both hydrological and mechanical processes. Given ongoing land-use changes in Western Norway, improved understanding of the functions of protection forests and the implications of their management is essential for integrated risk management in the region. This study aims to quantify the mechanical reinforcement of the soil by the roots of the pioneering tree species Betula pendula Roth (silver birch) at a case study site in Western Norway. Additionally, the study explores the impact of human intervention on tree growth, and consequently on the dynamics of the reinforcement of soil by roots, by comparing data from naturally growing and pollarded trees. An extensive field and laboratory campaign was conducted, enabling the calibration of a spatio-temporal root reinforcement model for stand-scale applications. The estimated reinforcement effects of Betula pendula using the Root Bundle Model with a Weibull survival function (RBMw) range between approx. 2.5 kN m −1 and 13.1 kN m −1 . Pollarded trees take longer to achieve the same reinforcement effect as naturally growing trees, which might indicate that pollarding reduce the effectiveness of a protection forests. The collection and analysis of the dataset presented herein represents a novel effort in Norway, being the first dataset of this kind developed for any type of forest in Scandinavia. The results can be implemented in slope stability models to assess the mechanical effects of forests growth on the triggering of shallow landslides. The findings highlight that the establishment of protection forest for landslide hazard reduction is a long-term perspective measure, which requires thorough planning to ensure its reliability and effectiveness.