On the tree stability: Pulling tests and modelling to assess the root anchorage

Abstract In addition to increasing temperatures and exacerbating meteorological extreme events, climate change affects the frequency of windstorms, which impact the stability of trees in urban and periurban environments. Therefore, there is growing interest in developing models for predicting how root anchorage could influence tree stability. Root anchorage depends on roots morphology and architecture and their relative interactio n with soil. The present study aims to assess the safety factor (SF) of trees through a simple static model considering overturning moment and anchorage strength. 21 trees, in 5 sites located in 5 sites in Tuscany (North-Western Italy), were subjected to p ulling tests simulating the wind force. Pulling tests were executed following similar works. The applied load was assessed in relation with the RAR (Root Area Ratio) measured for each tree. Through the model is able to calculate the root plate radius (Rt). The results show that the low -load pulling test is effective in predicting the tree overturning load, and that tree stability is influenced by the equilibrium between the roots distribution and the lateral space to grow. Rt varied in the range of 4-12 tim es the stem radius and this multiplication factor resulted linked with mean rooting depth. This approach could be used for slope stability analysis when considering also the effects of root cohesion.