Quantifying effective wind loads on trees through analysis of crown reconfiguration (TreeCon)

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In the past 70 years, storms have posed the most significant natural hazard to European forests. Storm damage occurs when trees are exposed to destructive wind loads. Due to their widespread extent, winter storms caused the largest amounts of damaged timber. The significance of winter storms in terms of timber damage in European forests has increased in the last 30 years. Six out of the seven most severe winter storms occurred after 1990. In the past, coniferous tree species were particularly affected by damage from winter storms because, unlike deciduous species, they retain their needles throughout the year. Winter foliage efficiently facilitates kinetic energy transfer from the near-surface airflow to the tree crowns due to their large surface area exposed to the wind. Given the ongoing climate change, it can be expected that in the future, in addition to winter storms, convective storm events will become more frequent, leading to tree and forest damage year-round, especially in summer. The year-round occurrence of destructive convective storm events will diminish the advantage of seasonal foliage in deciduous tree species. Storm events can reduce the vitality of remaining stands in affected regions, induce secondary biotic natural hazards such as bark beetle infestations, and result in economic loss. Storm damage affects ecosystem services such as timber production, recreational functions, water and erosion control, and carbon dioxide sequestration. Catastrophic storms can significantly reduce forests' carbon dioxide sink capacity in a short exposure time. Comprehensive knowledge of wind loads acting on trees is fundamental to minimizing storm damage to trees and forests. (i) While numerous previous studies (including my own) have identified and described patterns of wind-tree interactions, (ii) there is still a fundamental knowledge gap concerning the absolute instantaneous magnitudes of wind loads that trigger wind-tree interactions. This fundamental knowledge gap exists because only rudimentary quantitative knowledge is available regarding the deformation (reconfiguration) of tree crowns under actual wind conditions. Reconfiguration plays a crucial role in determining the transfer of kinetic flow energy to tree crowns. The TreeCon project aims to address this knowledge gap. The expected results and associated new insights will contribute to minimizing future storm damage to trees and forests. To acquire this new knowledge, a novel, cost-effective measurement system will be employed and integrated with existing measurement systems, resolving previously unanswered questions and testing hypotheses. This measurement system is particularly suitable for studies on deciduous trees.