Data from: Axial conduit widening, tree height and height growth rate set the hydraulic transition of sapwood into heartwood

The size-related xylem adjustments required to maintain a constant
leaf-specific sapwood conductance (KLEAF) with increasing height (H) are
still under discussion. Alternative hypotheses are that: (i) the conduit
hydraulic diameter (Dh) at any position in the stem and/or (ii) the number
of sapwood rings at stem base (NSWr) increase with H. In addition, (iii)
lower stem elongation (ΔH) increases the tip-to-base conductance through
inner xylem rings, thus possibly the NSWr contributing to KLEAF. A
detailed stem analysis showed that Dh increased with the distance from the
apex (DCA) in all rings of a P. abies and a F. sylvatica tree. Net of DCA
effect, Dh did not increase with H. Using sapwood traits from a global
dataset, NSWr increased with H and decreased with ΔH, and the mean sapwood
ring width (SWrw) increased with ΔH. A numerical model based on anatomical
patterns predicted the effects of H and ΔH on the conductance of inner
xylem rings. Results suggested the sapwood/heartwood transition depends on
both H and ΔH, and is set when the C allocation to maintenance respiration
of living cells in inner sapwood rings produces a lower gain in total
conductance than investing the same C in new vascular conduits.