2:45 PM - 3:00 PM
[MIS11-05] Measuring mechanical stress on tree trunks - regarding snow and wind
★Invited Papers
Keywords:strain gauge, forest damage, snow pressure, wind load
Trees live under constant mechanical stress from wind, snow, and their own weight. Knowing the balance between the magnitude of these physical loads and the mechanical strength of trees is important not only to advance our understanding of tree growth and species distribution in the natural environment but also from the perspective of forest damage prevention. However, there are not many methods that can directly measure the magnitude of external forces and the magnitude of mechanical stress acting on trees in the field. Previous studies have mainly used strain gauges (e.g. Ennos 1995, Blackburn 1997), displacement meters (e.g. Milne 1991), accelerometers (e.g. White et al. 1976), and clinometers (e.g. Fresch & Wilson 1999). Among these, strain gauge is more suitable for field measurements because the sensor itself is small and inexpensive, and it enables us to perform multiple measurements. By using strain gauges, the deformation of trees due to compression and tension can be directly measured with high accuracy and frequency, and the measured values obtained can be used as a direct indicator of the mechanical stress of trees. Examples of research using strain gauges on trees include examining the magnitude of stress exerted on root plates due to artificial loads (Ennos 1995), measuring dynamic moments caused by wind (Moore et al. 2005, Minamino & Tateno 2014), and attempts to quantify wind damage risk by measuring moments (Suzuki et al. 2016, Duperat et al. 2020).
Following these studies, we developed a method to measure the total amount of wind load, its centroid, and the direction acting on tree trunks using strain gauges (Miyashita & Suzuki 2020) to quantify wind damage risk and to elucidate the mechanism of wind damage occurrence. Wind damage is the biggest cause of forest damage in Japan. Especially in plantation stands it is known that thinning, which is essential for growing healthy stands, increases the risk of wind damage (Cremer et al. 1982, Mitchell 2013). However, there are few actual measurements, and it is not clear how much the risk increases by a thinning method. In addition, it is difficult actually to measure the wind profile within a forest, so our method, which can separately measure the wind load, its centroid, and the direction, is expected to contribute to more accurately assess the risk of wind damage to trees within the forest.
Strain gauges have been mainly used to evaluate the mechanical stress on trees due to wind, as mentioned above, and there have been no examples of measurements related to snow. To understand changes in the trunk shape of beech trees and their possible distribution range depending on the snow environment, we measured the deformation of beech trunks during the snowy period in a heavy snowfall mountain. Together with strength tests on the green wood of beech trees, we estimated the amount of mechanical stress (bending stress) that beech trunks receive during snow cover. Measurements were carried out on beech trees of different sizes at locations with different slope angles and snow depths, and the results clarified the relationship between the growth of beech trees and the snow environment.
In this presentation, I would like to focus on our studies and introduce the mechanical stress that trees receive from wind and snow, and what can be revealed by those measurements.
Following these studies, we developed a method to measure the total amount of wind load, its centroid, and the direction acting on tree trunks using strain gauges (Miyashita & Suzuki 2020) to quantify wind damage risk and to elucidate the mechanism of wind damage occurrence. Wind damage is the biggest cause of forest damage in Japan. Especially in plantation stands it is known that thinning, which is essential for growing healthy stands, increases the risk of wind damage (Cremer et al. 1982, Mitchell 2013). However, there are few actual measurements, and it is not clear how much the risk increases by a thinning method. In addition, it is difficult actually to measure the wind profile within a forest, so our method, which can separately measure the wind load, its centroid, and the direction, is expected to contribute to more accurately assess the risk of wind damage to trees within the forest.
Strain gauges have been mainly used to evaluate the mechanical stress on trees due to wind, as mentioned above, and there have been no examples of measurements related to snow. To understand changes in the trunk shape of beech trees and their possible distribution range depending on the snow environment, we measured the deformation of beech trunks during the snowy period in a heavy snowfall mountain. Together with strength tests on the green wood of beech trees, we estimated the amount of mechanical stress (bending stress) that beech trunks receive during snow cover. Measurements were carried out on beech trees of different sizes at locations with different slope angles and snow depths, and the results clarified the relationship between the growth of beech trees and the snow environment.
In this presentation, I would like to focus on our studies and introduce the mechanical stress that trees receive from wind and snow, and what can be revealed by those measurements.