The iLand core model includes the main processes like growth, mortality and regeneration. Additional sub models are technically organized and bundles in "modules" or "plugins". Typical examples for such modules are disturbance agents like wildfire and wind.
Applying a "plugin" approach simplifies switching between different versions or types of sub modules and provides due to a clean separation between main model and modules an fairly easy way for third party contributors to add own sub modules to iLand.
However, from a model user point of view, a module does not differ from the core iLand model: a section in the project file is specific for the module (including the enabled switch)).
- the fire module simulates the ignition, spread and the impacts of wildfire on the landscape scale
- the wind module simulates the disturbance agent wind on landscape level
- the barkbeetle module simulates spruce bark beetles (Ips typographus)
- the biotic disturbance engine (BITE) provides a general framework for simulating biotic disturbances
A special disturbance module in iLand is BITE (the BIotic disTurbance Engine). BITE is a general model to simulate biotic disturbances in forest ecosystems. It is a modular and simple model that is general enough to simulate a wide range of biotic disturbance agents, from fungi to large mammals. The BITE page contains information about how to use BITE in iLand.
The project file contains a special section (modules) that contains options for each module in a sub section. See the documentation of the respective module for details. Each subsection provides at least an enabled switch, e.g. modules.fire.enabled is used to toggle on/off the fire module.
Modules may include specific outputs similar to core iLand organizing outputs. Like iLand core outputs, settings for module specific outputs are located in the output section. Again, details can be found in the module documentations.
Modules are 'activated' or run once a year. This happens late in the simulation sequence, immediately before aggregating final stand statistics. If more than one modules is active, for each year the sequence of module activation is randomly varied and applied for the whole landscape.
The implementation of 'modules' in iLand is heavily based on the plugin mechanism of Qt and the use of interface classes in C++. Currently, all available modules are linked statically into the main executable of iLand and optionally enabled.
A module has three main entry points (defined in the DisturbanceInterface)
- setup(): general setup of the module. The function is called after the model space is allocated but before initialization. Another interface function (setupResourceUnit()) (installed by adding the SetupResourceUnitInterface) can be used to handle specific setup per resource unit. This allows using the environment file mechanism.
- beginYear(): is invoked at the beginning of every year - the dedicated slot to do some cleanup/setup.
- run(): the main function of the module (see also above)