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The L-ALMOND model: a functional-structural virtual tree model of almond tree architectural growth, carbohydrate dynamics over multiple years

DeJong, T. M., Da Silva, D., Negron, C., Cieslak, M., Prusinkiewicz, P.
Acta horticulturae 2017 no.1160 pp. 43-50
almonds, branching, canopy, carbohydrates, carbon, fruit trees, models, mortality, orchards, peaches, plant organs, planting, pruning, shade, tree growth
More than two decades of modelling research resulted in the L-PEACH model which used L-systems to simultaneously simulate the architectural development and carbohydrate dynamics (assimilation, transport, distribution, storage and remobilization) of growing peach trees. L-PEACH combined the supply/demand concepts of carbon allocation of a previous PEACH model with an L-systems model of tree architecture to create a distributed supply/demand system of carbon allocation in a three dimensional, growing, virtual tree. The L-PEACH model was expressed in terms of modules that represent plant organs. Organs were represented as a set of elementary sources and sinks for carbohydrates and the whole plant was modeled as a branching network of modules (i.e. organs) connected by conductive elements. A primary objective of the current research was to demonstrate the versatility of the L-systems-based modular approach for modeling fruit trees by converting the L-PEACH model to an L-ALMOND model. To do this initially required merely substituting the peach parameters for each of the different organ types (modules) with values appropriate for almond, based on data from previous experiments. However, the L-PEACH model accommodated manual pruning of simulated trees and pruning was always practiced when simulating tree growth over multiple years. This resulted in substantial reduction in tree (and L-string) complexity after each pruning when running the L-PEACH model. Since almond trees are rarely pruned much after the 2nd year in an orchard, simulation of almond tree growth without pruning resulted in unrealistically dense simulated canopies, and exponentially increased L-string complexity with time and unsatisfactory rates of virtual tree simulation. To overcome this, a function for simulating stem/spur mortality based on within-canopy shading was developed. The current L-ALMOND model is able to successfully simulate almond tree growth and development and produce realistic estimates of tree size, structure and productivity over seven years after initial planting.