On the applicability of the pipe model theory on the chestnut tree (Castanea sativa Mill.)

Abstract

Key message Leaf to sapwood area ratio in Castanea sativa is constant within a branch, but decreases with branch height. We propose a modeling approach to mitigate this effect. The pipe model theory postulates the constancy of the relationship between leaf to sapwood area among single parts and for a whole tree. By analyzing 218 branches belonging to 67 different chestnut trees (Castanea sativa Mill.), we tested the correctness of this postulate at three different levels: intra-branch, among different branch types (structural crown branches vs. epicormic branches), and within structural branches of the same trees. Results confirm the constancy of the leaf to sapwood area ratio (AL:AS ratio) at the intra-branch level, but show variability among branches within a tree. The AL:AS ratio of crown branches declines with height. Furthermore, epicormic branches display enhanced sturdiness with respect to crown branches. A generalized linear mixed modeling approach was used to explain the intra-tree AL:AS ratio variability of structural crown branches. The main explanatory variable on the AL:AS ratio within a chestnut tree was found to be the height of the branch insertion. To neutralize this effect when comparing the AL:AS ratio among different trees for general environmental and physiological studies, we propose the concept of the AL:ASground consisting of the AL:AS ratio of a hypothetical branch at ground level.