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Using L-Systems for modeling the architecture and physiology of growing trees: an exercise in building a tree model without a plan (ATTENTION! Lieu : Amphithéâtre Jacques Alliot, CIRAD)

Ted DeJong
Department of Plant Sciences, UC Davis
on 2011/09/08 at 11:00


Modeling architectural growth of trees is particularly challenging because of the phenotypic plasticity of trees in terms of size, shape and structure. Whereas plants in a field of corn or sunflowers often look very similar, casual observation of an orchard or woodland indicates that it is rare that trees of the same species have the same structure. Awareness of this phenotypic plasticity led me to abandon any ideas of developing deterministic models of tree growth. Instead I have pursued the notion that tree (plant) growth is driven by the development and growth of collections of semi-autonomous organs that depend on other organs to supply carbohydrates, nutrients and/or water. To a large extent the development of the L-Peach model has been an attempt to test this hypothesis. Testing this hypothesis required that we build a model that is focused on the development, growth and physiological behavior of all of the individual types of organs of the tree and have mechanisms built into the model for transporting resources among all of the parts of the tree in ways that account for the context specificity of each organ relative to external environmental inputs and gradients of resources within the tree. To a large extent the L-Peach model has achieved this and documents that tree growth can be simulated satisfactorily using the semi-autonomous organ concept of plant organization. The process of developing the model has led to achieving several milestones in plant modeling including the development of algorithms for modeling carbohydrate source-sink interactions within a plant, a rational method for simulating long-term carbohydrate storage and mobilization in perennial parts of the plant, methods for modeling uptake and transport of water within the plant based on calculations of water potential of the organs in the plant, and robust models of individual organ development, growth and function. Much has been done and much is still left to be done but the real value in the modeling effort has been the platform it has provided for identifying gaps in our knowledge and developing an integrated understanding of tree growth and function.