Movement of terrain on slopes, unless intense, as in the case of landslides, is practically imperceptible and the deformed trunks of trees growing on slopes are detectors of these movements. The deformation of a tree trunk may therefore be considered as a continuous record of terrain movement for the period of tree vegetation life. The cause of trunk deformation is a slight change in the inclination of the terrain on slope that accompanies terrain movement, and to which the tree trunk adapts during its time growth development. Submitted article presents a proposal for a method that, based on the time dependence of the development of the curvature of a tree trunk, allows a calculation of the path length and rate of the slope terrain movement for either the whole or a particular time period respectively. The calculation of the path length of the terrain movement assumes that the horizontal position of the center of gravity of the tree trunk remains unchanged in time and space, and the horizontal component of the terrain movement path is given by the horizontal distance of the center of gravity of the tree trunk from the heel of the trunk. The rate of movement is calculated from the terrain movement path length and age of the tree, which is determined from the diameter of the trunk. The position of the trunk's center of gravity is calculated from the digitized shape of the trunk according to the principles of solid body mechanics. 2 Calculation of Slope Terrain Movement Rate from Tree Trunk Deformation Karel Vojtasik Department of Geotechnics and Underground Engineering, VSB -Technical University of Ostrava, Ostrava, 708 00, Czech Republic karel.vojtasik@vsb.cz April 2026 Abstract Movement of terrain on slopes, unless intense, as in the case of landslides, is practically imperceptible and the deformed trunks of trees growing on slopes are detectors of these movements. The deformation of a tree trunk may therefore be considered as a continuous record of terrain movement for the period of tree vegetation life. The cause of trunk deformation is a slight change in the inclination of the terrain on slope that accompanies terrain movement, and to which the tree trunk adapts during its time growth development . Submitted article presents a proposal for a method that, based on the time dependence of the development of the curvature of a tree trunk , allows a calculation of the path length and rate of the slope terrain movement for either the whole or a particular tim e period respectively. The calculation of the path length of the terrain movement assumes that the horizontal position of the center of gravity of the tree trunk remains unchanged in time and space, and the horizontal component of the terrain movement path is given by the horizontal distance of the center of gravity of the tree trunk from the heel of the trunk. The rate of movement is calculated from the terrain movement path length and age of the tree, which is determined from the diameter of the trunk. The position of the trunk's center of gravity is calculated from the digitized shape of the trunk according to the principles of solid body mechanics. Keywords slope, terrain, movement, rate, deformation, tree trunk 1 Introduction Terrain movement is a phenomenon seen commonly on the Earth's surface. The innate incentive of terrain movement is gravity boosted by hydrodynamic forces of groundwater flowing through the terrain. In addition to these factors, movement is influenced by ge omorphology, terrain slope, terrain profile and vegetation (Clague and Stead 2012). Human activity can contribute to terrain movement too and it can it initiate or make it more intensive. The terrain movement intensity in general can vary widely, ranging from barely noticeable creep to significant ground shifts like landslides. Terrain movement classifications are assessed through various methodologies (Selley et al., 2005; Rollins and Zekkos, 2012) and some are based on a rate of terrain movement. Unlike s ubjective descriptive verbal methods of assessing terrain 13 Figure 9: Graph of trunk axis. Up to the age of 24 years, the terrain slope increases (see Fig. 1 b). After 24 years till the present time there is a barely noticeable change of the course of the trunk axis, but it generally points at negligible decrease of terrain slope (see Fig. 1 a). The calculation of the tree rate movement in the intervals of tree growth, as well as the extent of this interval, depends on the value of the annual increment of the trunk diameter, which is taken constant, though in fact it could be affect by some other factors. Thus both the time intervals and respective calculated rates of terrain movement could be seen as only approximate. Improving the result would require individual determination of the age of individual sections of the trunk according to tree rings, which is theoretically possible, but in reality impractical. The development of the rate of terrain movement demonstrates the general effect of trees in stabilizing slopes prone to sliding. With expanding of a root net the terrain is progressi vely reinforced. With increasing age of tree there in the terrain develops natural structure acting similarly like a gravitational wall. In the example, a coniferous tree with a single trunk is analysed. This approach could also be used for deciduous trees with multiple trunk branches. In such a case, however, there is in the analysis need to create a fictitious stem that substitutes all trunk branches. This additional substitution makes the analysis difficult but does not disqualify it from determining the rate of terrain movement. The shape of the tree trunk might result from many other factors beyond terrain movement, like irregular growth of the tree's canopy due to prevailing wind patterns, obstruction from nearby objects casting a shadow on it, and po tentially human activities. Before applying this