Quantifying the ability of trees to dissipate energy during a rockfall impact after a forest fire
Abstract ID: 3.10610 | Accepted as Poster | Poster | TBA | TBA
Estelle Noyer (1)
Lukas Kramer (2)
(2) Bern University of Applied Sciences, Solothurnstrasse 102, 2500 Biel/Bienne, CH
Over the last few decades, the increase in high-intensity forest fires that are difficult to control and the growing risk of fires in no originally fire-prone areas have given rise to concern among forest managers. In addition to the high mortality of trees, leaving a significant number of standing burnt stems, the structural damage caused by fire can vary from a reduction in the volume of the crown to the partial destruction of the root system, through to carbonisation of the wood of standing stems. On a finer scale, the mechanical properties of stems following a forest fire are poorly reported. However, the impact of heat treatment on wood properties is better known. Associated with a loss of mass, treated wood will show improved material hardness and durability over time, but also greater vulnerability to impact and a reduction in modulus of rupture, demonstrating a potential alteration in the mechanical properties of the stem. To quantify the impact of fire on the protective effect against rockfalls, current used models describe the protective effect of a forest as a function of stem density (i.e. probability of impact) and the ability of trees to dissipate energy on impact with a block (Ediss). However, these models were calibrated on healthy trees, implying homogeneous wood properties in the tested scenarios. This work therefore aims to estimate the maximum energy dissipation capacity of burnt trees in order to assess the protective effect of a forest after a fire. To do so, we proposed a new equation to compute Ediss at individual scale. The calibration is conducted through laboratory tests on a series of green and artificially burnt stems. In parallel, we conducted a case study using stems sampled in Bitsch forest (Wallis, CH), where the forest suffered an intense and uncontrollable forest fire in July 2023. Finally, the impact of the new Ediss values on the protective effect against rockfall of the forest stand was quantified using RockyFor3D software.
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