Trees bend and break when exposed to external forces such as wind, rockfall, and avalanches. A common simplification when modelling the tree response to these forces is to simplify the system as a clamped beam which means that the stem deflection is related to the stem flexibility only. However, a certain part of the stem deflection originates from rotation of the root-soil plate. In this paper, we investigate this contribution to the overall stem deflection. Norway spruce (Picea abies (L.) Karst) trees were subjected to winching tests to analyse the anchorage mechanics of the tree. The tests were performed at two experimental sites with an average slope of 32 and 34°and one site with a nearly flat ground in subalpine forests near Davos, Switzerland, during the vegetation periods of 2003 and 2004. The trees were pulled downslope with a winch and the applied force, stem base rotation, and the angle of the applied force relative to the stem were recorded. After the tree had fallen over, stem diameter and branch mass were measured for every meter segment. These data were used to model the tree in the finite element software ANSYS Ò , which was used for calculating the rotational stem base moment as
The reactions of trees to wind, rockfall, and snow and debris flow depend largely on how strong and deformable their anchorage in the soil is. Here, the resistive turning moment M of the root-soil system as a function of the rotation at the stem base plays the major role. M() describes the behavior of the root-soil system when subject to rotational moment, with the maximum M() indicating the anchorage strength M a of the tree. We assessed M() of 66 Norway spruce (Picea abies L. Karst) by pulling them over with a winch. These 45-to 170-year-old trees grew at sites of low and high elevation, with a diameter at breast height DBH=14-69 cm and a height H =9-42 m. M() displayed a strong nonlinear behavior. M a was reached at a lower for large trees than for small trees. Thus overhanging tree weight contributed less to M a for the large trees.Overturning also occurred at a lower for the large trees. These observations show that the rotational ductility of the root-soil system is higher for small trees. M a could be described by four monovariate linear regression equations of tree weight, stem weight, stem volume and DBH 2 ·H (0.80
Among others, the protective effect of the forest against natural hazards is mostly co-determined through the mechanical stability of the trees. Despite this, there is a lack of quantifiable knowledge regarding the mechanical interaction between the trees, the forest and natural hazards. With experiments conducted on spruce trees,and mechanical modelling of trees and tree trunks, the mechanical properties and the energy absorption capacity for a single tree during a rock impact were determined. It was shown that the anchorage properties correlated well with the volume of the tree stem. The four-point bending tests and the dynamic impact tests enabled us to determine the strength of the tree stems. Furthermore, the obtained values for the strength of the tree stems were strongly affected by the wood quality and sometimes deviated substantially from the established material properties of dried wood used for buildings. The behavior of trees when impacted by rocks could be simulated with full-scale impact tests and the energy absorption capacity quantified. These experiments gave important knowledge of how to analyze the interaction between natural hazards, trees and forests,with the focus on Norway spruce. However, to quantify the protection effect of the forest against natural hazards,more experiments on different tree species are required.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.