Biomass dynamics of higher-order tree branches: An analysis of the model

Abstract

A sectional model for the biomass dynamics of freely growing branches of all orders is described. This model is an extension of the previously proposed sectional model for tree biomass dynamics and demonstrates a bell-shaped biomass dynamics of tree branches and, correspondingly, boundedness of the number of branch orders. An important element of the model for the branch system is the interverticil green biomass. The model is parameterized using the published field data on the lifespan of branches of different orders and the age when the biomass of spruce (Picea abies (L.) Karst.) skeletal branches reaches its maximum. Supplementing the model of biomass dynamics of the regular branch system with known spruce-specific growth features (such as the initial growth inhibition and the presence of interverticil branches) yields a good approximation of the model estimates to actual data. A putative mechanism for the emergence of interverticil branches (consisting in the response to improved conditions for tree growth) and their function during tree growth (replacement of regular branches unable to adequately respond) are described. Presumably, the emergence of sleeping (adventive) buds that give rise to the interverticil branches is initiated by an increase in the pressure of assimilates in the tree phloem system what also corresponds to the published data on the experimental decapitation of the Wollemia nobilis (Araucariaceae) branches.