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

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. Abstract 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 (A(L):A(S) ratio) at the intra-branch level, but show variability among branches within a tree. The A(L):A(S) 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 A(L):A(S) ratio variability of structural crown branches. The main explanatory variable on the A(L):A(S) ratio within a chestnut tree was found to be the height of the branch insertion. To neutralize this effect when comparing the A(L):A(S) ratio among different trees for general environmental and physiological studies, we propose the concept of the A(L):A(Sground) consisting of the A(L):A(S) ratio of a hypothetical branch at ground level.