Soil bioengineering techniques use willows as a construction material for stabilizing slopes and protecting river banks against erosion. The engineering calculability of soil bioengineering construction material is the basis and a prerequisite for the application of bioengineering construction projects. To learn more about the dynamic behaviour of the material, tests were conducted. These tests included observation of dynamic behaviour of trees under stress, investigation of load carrying capacity and bending properties. For this study, three and four year old trees of the specimen Salix purpurea L. were used. The tree was pulled into motion mechanically. Movements of structural elements were measured, thus inquiring about the relevance of leaves, twigs and branches on the tree. Pull and release experiments were undertaken while cropping the axes of the tree gradually and measuring its oscillation. The eigenfrequency of the tree was strongly related to the total mass of the tree. Cropping the tree elevated the eigenfrequency. With only the main axis left the eigenfrequency increased erratically. When only the main stem was left the tree vibrated in the form of a free, dampened oscillation. The damping ratio, which represents the decrease of the amplitude from one oscillation movement to the next, could not be derived clearly from the architectural properties of the trees.