Trees, drought and wind
| When |
Dec 03, 2019
from 02:00 to 03:00 |
|---|---|
| Where | Room André Collet (M6) |
| Attendees |
Alexandre Ponomarenko |
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I will present two series of experiments on trees under stress: wind stress and water stress.
Wind stress. During strong wind storms trees break down. We compared the maps of strong winds and quantity of broken trees and observed a critical wind speed of 40m/s above which all trees are broken. We show that the shape of trees and the mechanics of fracture explain this universal speed of wind to break trees.
Water stress. During prolonged droughts, water starts to be missing in the ground but the leaves of trees still continue to evaporate. This causes water in trees to be in extreme conditions: at large negative pressure where the water is in a metastable state and can boil causing gas embolism of the trees and eventually killing them. While in laboratories experiments water can be metastable down to -20MPa, in plants water will become gas at critical pressures varying from -1MPa to -20 MPa depending on trees species. The ultimate goal is to understand what sets the critical pressure for each species of tree. We are far from that. I will present experimental set-ups that we developed to be able to observe gas embolism propagation in trees.