Analyzing key factors of roots and soil contributing to tree anchorage of Pinus species

KEY MESSAGE: Root anchorage strength and stiffness can be represented by small number of root and soil parameters. Root morphology represents the majority of these factors. Tree anchorage is a primary function for plant survival which may reach its limit under extreme conditions such as windstorms. To better understand the processes and influential factors underlying tree anchorage, we analyzed the mechanical effects of root morphology and the material properties of roots and soil on the tree-overturning process with the recently developed finite element model RootAnchor. The root system was represented by a simplified 3D root pattern derived from an ensemble average of seven measured root systems of 19-year-old Pinus pinaster grown in sandy spodosol. Soil properties were measured by direct shear tests. Taguchi orthogonal arrays were used to examine the sensitivity of the geometric and material factors of roots and soil to tree anchorage. Tree anchorage was characterized by anchorage strength TMc and anchorage stiffness K0. Using a small number of numerical experiments, the sensitivity analysis prioritized only two key factors contributing to tree anchorage among the 34 factors considered. The results showed root morphological traits that played a dominant role in the material properties of roots and soil in tree anchorage. Taproot depth, the dimensions of the Zone of Rapid Taper (ZRT) and basal diameter of the windward shallow roots were the key factors contributing to TMc (variations > 8%). The dimensions of the taproot, root and soil stiffness, and the basal diameter of the leeward shallow roots were the most active factors for K0 (variations > 10%). These results provide insight into simplified tree anchorage expressions for the prediction of wind-induced uprooting.