- Products and services
- Resources and support
- About us
- Log in/Register
The model illustrates three types of submodel and is an example of a spatial model implemented in Simile. It shows that Simile is capable of handling quite complex spatial behaviour — in this case, landuse change in which the neighbours of a patch influence the likelihood of transition from one landuse state to another — even though Simile has no built-in constructs for spatial modelling.
The model illustrates three types of submodel:
The model works as follows. Each patch contains a state variable (the compartment “state”) which defines the state it starts off in. This is 1 for forest and 2 for crop. If a crop patch has been a crop patch for a certain length of time, then it is abandoned and reverts to forest (as mediated by the variable “change to forest”). If the volume of the trees exceeds a certain amount and the patch has crop neighbours (this is why we need to know which patches are next to which others), then the forest is cleared and it changes to crop as the landuse (as mediated by the variable “change to crop”).
The following figure show how the model behaves, using Simile’s grid map display to show the patches on a spatial basis. The light (yellow) squares represent the patches under crop; the dark (green) squares represent forest. When users request this display, they are required to specify a variable indicating the column number for each patch, and the actual variable to be displayed: Simile then has sufficient information to lay the patches out in the correct grid-based manner. This display shows how Simile can handle spatially-referenced information, even though it has no built-in concept of spatial modelling.
Initially, most of the area is forest, with a band of cropping land on the left. After 40 years, patches of forest on the forest margin have been cleared, leading to a ragged edge to the forest boundary. In this particular run, the model was set up so that there was no reversion of cropped land back to forest, but as indicated above it has been designed to allow for this to happen.
Download the model file from the model catalogue entry to see how the spatially-explicit model is formulated.