Forest structure, competition and plant-herbivore interaction modelled with relational growth grammars

Relational Growth Grammars are systems of rewriting rules (graph grammars) with graphical interpretation. They allow a feedback from the created virtual 3-d structures to the subsequent ruleapplication process. Using them it is possible to combine morphological (genetically fixed) growth rules with environmental impact and with functions evaluating the competitive situation of individual plants. Relational Growth Grammars are thus an ideal tool for precise specification of functional-structural models of plant growth and architecture. The dynamics of stand development in such models results from purely local rule application. Preliminary results are shown for three applications in forest-ecosystem modelling: (a) Creation of irregular stand structures, (b) simulation of competitive effects on crown radius development and resulting stand dynamics, and (c) modelling the interaction between trees and herbivores, based on the energy budgets of the individual plants and animals. The latter model includes genetical transfer and evolution of the foraging strategy of the animals. The software system GroIMP (Growth-grammar related Interactive Modelling Platform), an open source project available under www. grogra.de, was designed to interpret Relational Growth Grammars in an object-oriented framework. It also serves to visualize the resulting spatial structures. The code, executable by GroIMP, for the abovementioned models is completely documented and explained. By our examples, we hope to motivate the readers to use rule-based structural models in forest ecology