Effects of cambial age and flow path-length on vessel characteristics in birch

Abstract

The distribution of vessels in broadleaf timber, is directly related to water transport efficiency and safety. Here, I tested the hypothesis that vessel characteristics depend on cambial age (CA) and flow path-length (PL) within the tree rather than solely on CA by measuring vessel hydraulic diameter (VD), vessel frequency (VF), theoretical specific hydraulic conductivity (ks), and theoretical implosion resistance (VIR) in every growth ring of birch (Betula platyphylla Roth.) tree root, trunk, and branch samples. The effects of CA and PL were analyzed using a linear mixed model. Differences in the vessel characteristics are significant between CA, between PL, and between the interaction of CA and PL. VD decreased linearly and VF increased nonlinearly with PL. The PL explained 59.3 and 67.3 % of the longitudinal variation in VD and VF, respectively. ks decreased nonlinearly and VIR increased linearly with PL. The PL explained 25.6 and 43.3 % of the longitudinal variation in ks and VIR, respectively. Radial changes were evident above ground, VD increased, and VF decreased with CA for the first 10–20 years and remained constant thereafter. ks exhibited a logarithmic increase and VIR exhibited logarithmic decrease with CA. Variable radial patterns were observed below ground. The CA explained 30.9–98.8 %, 23.7–96.9 %, 42.9–96.8 %, and 50.9–98.5 % of the radial variation in VD, VF, ks, and VIR, respectively. The results suggest that vessel characteristic changes are determined by CA and PL. While growing, trees adjust their vessels to maximize water transport efficiency and ensure mechanical safety.