SIMWAL: A structural-functional model simulating single walnut tree growth in response to climate and pruning

Abstract

SIMWAL (SIMulated WALnut) is a structural-functional tree model developed for single young walnut tree (Juglans sp.). It simulates the 3D structure dynamics of the tree, and biomass partitioning among its different organs, for a period ranging from a few months to several years, according to climatic conditions (temperature, radiation and air CO2 concentration) and pruning. The aerial part of the tree is represented by axes split into growth units, inter-nodes, buds and leaves. The root system is described very coarsely by three compartments (taproot, coarse root and fine root). Only carbon-related physiological processes, i.e., radiation interception, photosynthesis, respiration, photosynthate allocation, and reserve storage and mobilisation are taken into account. Water and mineral nutrients are assumed to be optimal. We describe the model, and present preliminary tests of its ability to simulate tree architecture dynamics and carbon balance compared with field observations. Data requirements, and limits and improvements of the model are discussed.