The Property documentation for the Stocks and Flows Package is also included here because it is very closely integrated with ST-Sim, and, like ST-Sim, it is developed by ApexRMS.
Project Properties (often referred to as Definitions) are basic building blocks that are shared between Scenarios. For example, each Stratum can be refrenced from a Scenario's Transition Multipliers or State Attribute Values.
Scenario Properties are unique to each Scenario, and can be varied independently to create "what if" simulations. Some important groups of ST-Sim Scenario Properties are:
1. Initial Conditions
Initial Conditions are a set of starting points for any model. In ST-Sim, there are two types of Initial Conditions:
- Non-Spatial Initial Conditions
- Spatial Initial Conditions
Each type of ST-Sim initial condition has its own Property that can be configured independently.
2. Transition Pathways
The most advanced Scenario Property is the Transition Pathways Property. This Property lets you configure the Deterministic and Probabilistic transitions for a Scenario using a graphical editor called the Transition Diagram.
3. The Spatial Properties
The Spatial Scenario Properties, which normally appear in the Transitions - Spatial group, represent an advanced set of features which can be used when running the model spatially. These properties define the rules by which transition probabilities vary in space as a function of the state of each cell on the landscape. Users can specify the size distribution for fast spreading transitions like fire, the dispersal kernel or spread distribution for slow spreading transitions such as the spread of invasive plants, the patch prioritization for transitions (smallest vs. largest and edges vs. interior), spatial multipliers for transition probabilities, direction multipliers to capture the effect of processes such as the influence of wind on fire spread rates, slope multipliers to capture the effect of processes such as the influence of topography on fire spread rate, and adjacency multipliers to capture the effect of a cell's neighborhood on transition probabilities.
4. The Time-Since-Transition Properties
The Time-Since-Transition (TST) properties allow users to define how transitions depend on the transition history of a cell. For example, you may want to define a Fuel Buildup pathway that can only occur after a certain amount of time has elapsed since the last Fire has moved through a stand. In the probabilistic transitions property you would set a Min TST value for this pathway that corresponds to the time required without fire for a fuel buildup to occur; in the time-since-transition groups property you would set the Fuel Buildup transition type to depend on the Fire transition group; and in the time-since-transition randomization property you would define the initial time since transition distribution for each cell on your landscape.
Attributes represent a set of advanced properties which can be used to roll up simulation results according to areas aggregated by either state classes or transitions. In addition, attributes can also influence run outcomes with the use of targets or adjacency multipliers.
6. Stocks and Flows
This set of features provides the ability to track, for each simulation cell, pools of stocks (e.g. carbon) and flows between pools (e.g. carbon fluxes). The stocks and flows are completely customizable: users can define any number of stocks and flows; furthermore flow pathways can occur automatically each timestep (e.g. biomass growth of carbon in forests), or they can be triggered by a transition in the STSM (e.g. carbon emissions due to fire). The ST-Sim stock-flow module has been designed to allow for the rapid development of IPCC-compliant Tier 2/3 greenhouse gas inventories associated with Agriculture, Forestry and Other Land Use (AFOLU).