(1)

Reversible changes in bark thickness depend on three processes. First, changes in bark hydraulic capacitance (component 1), expressed by the symbol D _b^ΨP,x in the text; second, changes in bark osmotic concentration (component 2) caused by lateral solute fluxes, i.e.D _b^ΨΠ,b; third, xylem conduit diameter response to xylem tension (component 3), i.e.D _x^ΨP,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):