Individual-based modelling of a population of trees

The main aim of this tutorial is to introduce you to individual-based modelling.

System Dynamics (or “compartment-flow”) modelling generally does not represent individuals in a population. Instead, all the individuals are lumped together and represented by a single value: the number of individuals in a population, the total weight of all the individuals, or the total amount of some substance they contain (water, carbon or nitrogen, for example).

However, there are many situations when it is important to represent each individual in the population separately. For example, the behaviour of the whole population may be partly a product of interactions between individuals, or between individuals and their environment.

In this tutorial, we will look at how to model a population in terms of a set of individuals — in this case, trees. We will not consider how to handle interactions. Another tutorial, involving the modelling of the interaction between trees and crops, will be available shortly. However, we will see how to specify a set of individuals, how to give them individual behaviour (growth), and how to represent the creation of new trees and the death of existing ones.