Application of the GreenLab model to simulate and optimize wood production and tree stability: a theoretical study

Abstract

Qi, R., Letort, V., Kang, M., Cournède, P-H., de Reffye, P. & Fourcaud, T. 2009. Application of the GreenLab model to simulate and optimize wood production and tree stability: a theoretical study. Silva Fennica 43(3): 465-487.The GreenLab model was used to study the interaction between source-sink dynamics at the whole tree level, wood production and distribution within the stem, and tree mechanical stability through simulation and optimization. In this first promising numerical attempt, two GreenLab parameters were considered in order to maximize wood production: the sink strength for cambial growth and a coefficient that determines the way the biomass assigned to cambial growth is allocated to each metamer, through optimization and simulation respectively. The optimization procedure that has been used is based on a heuristic optimization algorithm called Particle Swarm Optimization (PSO). In the first part of the paper, wood production was maximized without considering the effect of wood distribution on tree mechanical stability. Contrary to common idea that increasing sink strength for cambial growth leads to increasing wood production, an optimal value can be found. The optimization results implied that an optimal source and sink balance should be considered to optimize wood production. In a further step, the mechanical stability of trees submitted to their self weight was taken into account based on simplified mechanical assumptions. Simulation results revealed that the allocation of wood at the stem base strongly influenced its global deformation. Such basic mechanical criterion can be an indicator of wood quality if we consider further the active biomechanical processes involved in tree gravitropic responses, e.g. formation of reaction wood.

Analysing the effects of local environment on the source-sink balance of Cecropia sciadophylla: a methodological approach based on model inversion

“…However, given the particular candelabrum-like architecture of Cecropia and the great heights that they can reach rapidly, one hypothesis could be that the appearance of stilt roots, as well as the demand of the ring compartment, could be influenced by requirements to ensure the mechanical stability of the tree. This hypothesis could be investigated in parallel by both experimental and model-based approaches: indeed, since the calibrated model faithfully reproduces internode masses and dimensions along the main stem, it would be possible to calculate the biomechanical stresses in the trunk at each growth step, as done by Qi et al (2009) with the GreenLab model for a virtual tree. Thus, virtual experiments could be performed to help understand the potential relationship between ring increment or stilt root growth and the mechanical stability of the tree.…”

Stronger wind, smaller tree: Testing tree growth plasticity through a modeling approach

“…Differing from the conclusion that λ should be equal to 1 to obtain the maximal wood biomass ( Qi et al., 2009 ), here the influence of λ is more complex, as shown in Figure 8 . At a lower S layer value, e.g., S layer = 0.5, the trunk is thin and the diameter of the tree top is too slim to support itself.…”

“…However, as the sampling in such experiments is very costly, an in silico experiment remains an appealing tool to test hypotheses and inspire new thought. In a former study, the optimization of wood yield with the constraint of stability has been conducted ( Qi et al., 2009 ), which also attempts to find the best parameter for secondary growth. The current work differs from it in several aspects: first, the wind environment is considered, while the former is limited to gravity.…”

Modeling plant plasticity from a biophysical model

“…Taylor [2005] advanced this model and handled bio-mechanical simulation at branching points. Qi et al [2009] used the equilibrium equations adapted to conic beams, which simplified the process of bending.…”