Vegetation states
Vegetation states are a central concept in SVD. Every simulated cell is - at every timestep - in one of the possible states, and transitions between states are the mechanism how vegetation dynamics are expressed.
Definition of states
The potential states are defined by the setting states.file in the project file.
The table has the following columns:
| Column | Description |
|---|---|
| stateId | a unique numeric (integer) Id of the state. Ids should start with 1 (0 is reserved as an invalid state) |
| composition | a string describing the main species (see below) |
| structure | an integer class describing the structure (top canopy height class) (0..N) |
| fct | functioning, an integer class describing the vegetation density class (0..N) |
| name | a string with a label for the state (if omitted a label is constructed from composition, structure, and function) |
| type | a string describing the handling module (see below) |
Composition, structure, and functioning
From those three properties of a vegetation state, SVD currently only uses the composition internally and requires thus a specific format (the composition is used for calculating species shares in the neighborhood of a cell):
- A list of all allowed species is defined in
model.species. The preferred species coding scheme is a four character combination of genus and species (e.g., “Picea abies” -> “piab”) - the composition is a space-delimited string of up to four species (e.g. “PIAB fasy pisy”)
- uppercase species codes (e.g. “PIAB”) indicate the dominate species, lowercase species codes (“piab”) specify admixed species
- “unforested” is a special composition reserved for, well, a state without forest cover
Please note, that “species” could be defined more broadly, e.g. as mixture types or vegetation types.
Extra variables
Additional state specific variables can be added by using the states.extraFile table. Also modules can add state-specific variables (e.g. the fire module).
The type of a state
The type defines for each state the responsible “party”, i.e. the process / module that is the default “handler” for a particular state. The task of a handler is to determine future states of all cells that are currently in one of the handled states. See the modules page for more details.
Possible values for type are:
- blank: the handling process is the main DNN
- the name of a module: cells in this state are handled by the given module