Scenario properties

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A scenario consists of a collection values assigned to one or more scenario properties; together the values for all of the scenario properties represent the inputs to the model for that scenario. Typically a single property consists of one screen of inputs, organized according to property fields. The values assigned to each property for a particular scenario can be viewed and edited using the Scenario Editor.


Below is a description of all of the properties associated with a scenario in ST-Sim.


Run Control

The Run Control property specifies run control details for the current scenario. The fields for this property are:

Start timestep

The starting timestep for the simulation for which the initial conditions are defined (timestep zero by default).

End timestep

The final timestep for the simulation. The total timesteps simulated are equal to the difference between the end and start timestep

Total iterations

The number of replicates (i.e. Monte Carlos) for the simulation.

Run model spatially

If selected then the scenario will be run as a spatially-explicit simulation.

Pathways

The Pathways tab displays the Transition Pathways associated with the scenario, which allows users to edit Probabilistic Transitions and Deterministic Transitions.

Initial Conditions

The Initial Conditions tab is divided into two separate properties, one for Non-Spatial Initial Conditions and the other for Spatial Initial Conditions.

The Non-Spatial property specifies the total landscape area, the number of simulation cells and the distribution of relative area in each state class, stratum and age range combination at the start of the simulation. The optional Calculate from distribution checkbox sets the model to use the Relative Amount field from the Distribution table to define how many cells should be set for each record in that table. In this case the number of simulation cells will be calculated as the sum of the Relative Amount.

The fields for the distribution portion of the Initial Conditions property are:

Primary Stratum

The primary stratum for which the initial condition record applies.

Secondary Stratum (optional)

The secondary stratum for which the initial condition record applies.

State Class

The state class for which the initial condition record applies.

Age Min

The minimum age for which the initial condition record applies. Ages will be randomized between Age Min and Age Max for this record.

Age Max

The maximum age for which the initial condition record applies. Ages will be randomized between Age Min and Age Max for this record.

Relative Amount

The relative area assigned to the stratum-state class combination. This can be expressed as an absolute area (e.g. acres), or alternatively as a relative area (e.g. proportion or percent of entire landscape).


The Spatial Initial Conditions allows users to load up to four different raster files in GeoTIFF format. These are used to specify the following fields for each simulation cell in the study area:

Primary Stratum

typically vegetation type

Secondary Stratum (optional)

typically planning zone

State Class

Age (optional)

Note that aside from the values assigned to each cell, these raster files must be identical in terms of extent, location, number of rows, columns and spatial referencing system. Once the files are loaded, ST-Sim reports on the attributes of these files by displaying the number of rows and columns and the cell size. ST-Sim also calculates and displays the Cell size in the unites specified by the user under definitions, the Number of cells and the Total area of the landscape. Note that if ST-Sim is unable to recognize the area units specified in the raster files, the cell size and associated calculations may be wrong. In this case, users may choose to Override the Cell size calculation and specify their own value.

Transition Targets

The Transition Targets property allows users to define targets for the area to transition over time across the landscape for certain Transition Groups. The steps required to setup these values are typically as follows:

  1. Decide upon the transition groups for which you wish to set targets
  2. Create a set of records in the Transition Targets grid for the first timestep of your model run for which you wish to have a non-zero target. There should be one record for every possible combination of Stratum and Transition Group for which you would like to set a target for this first timestep. Note that prior to the first timestep in which a target is specified for a particular Stratum/Transition Group combination, the model assumes that this Stratum/Transition Group has no target. Any Stratum/Transition Group combinations for which no records are specified are assumed to have no target.
  3. Enter the Target Area for each record associated with this timestep. Any targets entered will be applied for this and all subsequent timesteps.
  4. If the target areas change over the course of the simulation, repeat steps 2-3 for any additional timesteps. Once a target area is entered for Stratum/Transition Group for a new timestep, the model will then apply this same target for that Stratum/Transition Group for every subsequent timestep (until a new record for this Stratum/Transition Group is encountered for a subsequent timestep). Any Stratum/Transition Group combinations for which no record is entered are assumed to have the same value as was set prior to this timestep (including no target value if none was set previously).

The fields and options for Transition Targets property are:

Primary Stratum (optional)

The stratum (Vegetation Type by default) for which the treatment applies. If no primary stratum is specified the target is applied across all primary strata.

Secondary Stratum (optional)

The secondary stratum (Planning Zone by default) for which the treatment applies. If no secondary stratum is specified the target is applied across all secondary strata.

Iteration (optional)

This value represents the iteration in which target area is specified. The target area continues through subsequent iterations until another Iteration value is encountered by the model for the same transition group in the same stratum, at which point the new values for target area will be applied. If no iteration is specified, the target will be applied across all iterations.


Timestep (optional)

This value represents the timestep in which target area is specified. The target area continues through time until another Timestep value is encountered by the model for the same transition group in the same stratum, at which point the new values for target area will be applied. If no timestep is specified, the target will be applied across all timesteps.

Transition Group

Represents the transition group for which target areas are specified.

Target Area

The target area for the combination of stratum, timestep and transition group.

Distribution Type (optional)

When using a probability distribution for area targets, users must specify a probability distribution for the area targets. At the moment either the Normal or Beta distributions are available for setting area targets.

SD (optional)

When using a probability distribution for area targets, users must specify a standard deviation value that can be sampled from a specified distribution.


Target Area Min (optional)

When using a probability distribution for area targets, users can specify a minimum value that can be sampled from a specified distribution.

Target Area Max (optional)

When using a probability distribution for area targets, users can specify a maximum value that can be sampled from a specified distribution.

Turning Transition Targets Off: Once transition target has been turned on at a particular point in time in a simulation, the only way to turn it off is to create a record for the specified set of conditions (i.e., Primary Stratum, Secondary Stratum, Transition Group, etc...) starting at the timestep during which you no longer wish for the transition target to be applied. This record should have both the Target Area and Distribution Type fields blank. The ability to turn Transition Targets off is only available for versions 3.1.37 or higher of ST-Sim.

A note on the transition target algorithm: For non-spatial simulations (or in version 3.0 for spatially simulated transition groups with no size distribution) ST-Sim applies targets by normalizing transition probabilities in order to meet the target and applying the same algorithm as would be used without targets. This is done by first calculating the expected level of the transition as the sum product of area and transition probability across all cells. Probabilities for this transition are then multiplied by the ratio of target to expected area such that the resulting expected area after normalization is equivalent to the target. For example, if the target for transition "A" was 100 ha and the expected level of transition "A" was 50 ha then all probabilities for this transition would be multiplied by 2. On average over many iterations, the model would achieve the target level of the transition. However, because probabilities are being used, one would expect some variability around the target in any one iteration. Note that in spatial simulations with size distributions the model applies transition events and stops as close as possible to the target, therefore for these types of transitions there is less variability around the target.

Output Options

The Output Options property provides users with control over the output generated for each model run.


The Summary output options allow users to specify the type and frequency of model output to be saved to the database. The Calculate as interval mean values option will report the average the area transitioned between the timesteps at which reporting occurs.


The Spatial output options allow users to save detailed raster GeoTIFF output durning a spatial model run. When this type of output is saved, users are able to view output maps of model variables directly in the ST-Sim user interface and to export these GeoTIFF files for post processing after the simulation is complete.

Advanced Scenario Properties

See the Advanced Scenario Properites page for details on properties shown in the advanced tab of the Scenario Editor.