(1)
Reversible changes in bark thickness depend on three processes. First, changes in bark hydraulic capacitance (component 1), expressed by the symbol D bΨP,x in the text; second, changes in bark osmotic concentration (component 2) caused by lateral solute fluxes, i.e.D bΨΠ,b; third, xylem conduit diameter response to xylem tension (component 3), i.e.D xΨP,x. The first two processes are driven by the radial fluxes, respectively, of water and solutes to and from the xylem into the bark. The third component is the result of a balancing act between soil water availability, atmospheric dryness and stomatal regulation of water loss at the leaf. Component 1 in Eqn. (1) is derived from Mencuccini et al. (2013). Therefore, the term marked as component 2 in Eqn. (1) above gives the net fraction of the changes in bark osmotic concentration that depends directly on the corresponding changes in xylem osmotic concentration. α, β and γ are defined as in Mencuccini et al. (2017):