A method for measuring the forces acting on a tree trunk using strain gauges

Mechanical Fatigue in Trees Mitigated by Annual Growth: a Theoretical Model

Mechanical forces applied over a period of time tend to cause fatigue failure in natural organisms and in engineering structures. Here, the theoretical approach known as Continuum Damage Mechanics is applied to study fatigue damage development in trees. It is found that growth in the form of an annual ring of new material is a very effective strategy to limit fatigue damage, due to the fact that, over time, each ring moves inside the trunk, reducing stress. If (as is generally assumed) the tree grows so as to keep the bending stress on its trunk constant, then fatigue failure will be effectively impossible until the tree is very old. One interpretation of this finding is that high cycle fatigue simply never occurs in trees: they don't accumulate fatigue damage but rather fail by instantaneous overload or low cycle fatigue during a single storm. Another interpretation is that the bending stress is maybe not kept constant but changes as the tree grows, which would be a more efficient strategy making the best use of material. These findings are considered using data from the literature and their implications for the creation of biomimetic products are discussed. Possible experiments to test these theoretical predictions are suggested.

Enhancing TreeMMoSys with a high-precision strain gauge to measure the wind-induced response of trees down to the ground

Measuring tree response to wind loads is fundamental for the process-based analysis of wind-tree interactions. Comprehensive knowledge of wind-tree interactions enables the further development of decision support tools available for estimating the probability of wind damage to trees. The assessment of critical wind loads that lead to damage is particularly important. This paper describes the inexpensive Tree Strain Sensor (TSS) suitable for precisely measuring the response of tree parts to external loads such as pulling tests and natural wind loading. It is an addition to the recently developed Tree Motion Monitoring System (TreeMMoSys) but can also be used as a standalone device, allowing measurements necessary to estimate effective wind loads on trees.