Vivien Bonnesoeur

Forest trees filter chronic wind‐signals to acclimate to high winds

Controlled experiments have shown that trees acclimate thigmomorphogenetically to wind-loads by sensing their deformation (strain). However, the strain regime in nature is exposed to a full spectrum of winds. We hypothesized that trees avoid overreacting by responding only to winds which bring information on local climate and/or wind exposure. Additionally, competition for light dependent on tree social status also likely affects thigmomorphogenesis. We monitored and manipulated quantitatively the strain regimes of 15 pairs of beech (Fagus sylvatica) trees of contrasting social status in an acclimated stand, and quantified the effects of these regimes on the radial growth over a vegetative season. Trees exposed to artificial bending, the intensity of which corresponds to the strongest wind-induced strains, enhanced their secondary growth by at least 80%. Surprisingly, this reaction was even greater - relatively - for suppressed trees than for dominant ones. Acclimated trees did not sense the different types of wind events in the same way. Daily wind speed peaks due to thermal winds were filtered out. Thigmomorphogenesis was therefore driven by intense storms. Thigmomorphogenesis is also likely to be involved in determining social status.

The influence of forest management systems on the environmental impacts for Douglas-fir production in France

The environmental wood profile, all over its life cycle, is a subject of interest for industries within the forest sector. Douglas-fir is a wood species with multiple applications and high productivity. In Europe, France is the country with the largest area dedicated to the cultivation of this tree species. This study aims to quantify the Douglas-fir forestry environmental impacts under different management practices performed in France. This study presents detailed life cycle inventories of both intensive and extensive scenarios, including all the processes from site preparation to logging activities. The results showed that stand establishment operations, tending and logging were the main stages responsible for the environmental impacts in both scenarios. The requirement of numerous thinning steps prior to the final cutting, which require machines with large fuel consumption, also had a negative influence. The logging stage, which includes the final cutting and the corresponding forwarding and loading onto trucks, also accounted for a significant contribution to all the categories. When the environmental results were compared with other life cycle studies on pine, eucalyptus and spruce, similar trends were identified in spite of the different management practices (low or high intensive scenarios), system boundaries and forest systems intensity (frequency of activities) considered.

Pas de vent, pas de bois. L’apport de la biomécanique des arbres pour comprendre la croissance puis la vulnérabilité aux vents forts des peuplements forestiers

La biomecanique etudie les reactions et adaptations des etres vivants a leur environnement mecanique, par exemple aux oscillations et forces exercees par le vent. Au-dela des theories anciennes de la securite mecanique constante, la mecanobiologie a recemment formalise les signaux mecaniques, la perception des cellules vivantes et les reponses de croissance. Ces mecanismes physiologiques font que l’arbre ne forme vraiment du bois, tissu de soutien, que lorsqu’il est mecaniquement stimule. La croissance est controlee par les deformations mecaniques percues, qui deviennent alors pour l’arbre de bons indicateurs de securite. Pour appliquer ces connaissances aux forets, le projet ANR FOR-WIND a l’ambition de developper une mecanobiologie adaptee aux temps longs et aux conditions naturelles complexes. L’enjeu est de concevoir les pratiques d’amenagement avec de nouveaux indicateurs de vulnerabilite aux vents forts, qui raisonnent l’effet du changement climatique, de la structure du paysage, de la sylviculture ou de l’amelioration genetique au travers des processus cles mais negliges d’endurcissement des arbres aux vents usuels.