WG2 aimed at reflecting on processes/mechanisms needed to understand the functioning of trees under both normal and (extreme) stress conditions. An inventory was started and resulted so far in a preliminary overview of:

• Existing mechanistic models that are used within the group (including time scale)
• The necessary data to run the models (meteo data, light response curves, water potentials, P50 values)
• Available datasets (control, stress, extreme events)
• Model calibration/validation of the models (normal or stress conditions? on which species? seasonal parameters?)
• Purpose of the modelling activities (wood production, wood quality or tree functioning)

Interesting discussion points were:

• Leaf/xylem ratio: Proportional in normal conditions? How does stress affects this?
• Sapwood area: How does it vary and why?
• Connectivity of vessels/tracheids: What do we know about radial water transport? Important or not? Link between 2D slice info and 3D network in a tree?
• Carbon, phloem, storage, growth, and remobilisation: There exist important knowledge gaps. Can we use phloem info (2D) for drought stress detection?

WG2 activities will focus on increasing the mechanistic understanding at a higher organisation level. This is illustrated in the figure below and will be used as starting point for future discussions.