Simple State Transition Model (SSTM)

The Simple State Transition Model (SSTM)is a very simple autonomous process plug-in that “ages” a landscape by providing for succession from different land use/land cover types (or any other variable represented in the IDU coverage). Succession is modeled using a transition table that defines transition probabilities and periods until transitions occur to any number of other classes. These transitions are specified in an Xml file, and the name of the file is specified in the Project file as the initialization string for SSTM.

The basic XML format for a SSTM input file is provided below.

<?xml version="1.0" encoding="utf-8"?>

<transitions>

  <!-- Decidous Forest--> 
  <trans start="Starting Code" end="Ending Code" period="Period" prob="Probability" /> <!-- first transition -->
  
  <!-- Evergreen Forest-->
  <trans start="Starting Code" end="Ending Code" period="Period" prob="Probability" /> <!-- second transition -->

  ... repeat as needed...
</transitions>

The format of this file consists of a <transitions> tag containing individual transition descriptors. Individual transition descriptors are defined by a <trans> tag with the following attributes:

AttributeDescriptionValueRequired?
start The Lulc class code for which this transition is defined. This is defined in the lulcTree input file. IntegerYes
end The Lulc class code for which this transition will result in. This is defined in the lulcTree input file. IntegerYes
period The average duration for the ‘start’ class before a transition occurs (years) IntegerYes
prob The probability that a transition will occur over the period (0-100)IntegerYes
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To include SSTM in an application, include the <model> entry shown below in the <models> section of the Project (envx) file. Note that the SSTM Xml input file is given as the initInfo argument. Note that specified files must be either in the ENVISION study area directory, or a fully-qualified path with directories must be provided.

<autonomous_processes>
  <model 
    name         ='State Transition Model' 
    path         ='sstm.dll' 
    use          ='1' 
    timing       ='0' 
    initInfo     ='sstm_nlcd.xml' 
  />

</model>
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Below is an example SSTM input file.

<?xml version="1.0" encoding="utf-8"?>

<!--  Transition Class defintions for a SSTM Model -->

<transitions>

  <!-- Decidous Forest--> 
  <trans start="41" end="43" period="25" prob="25" /> <!-- to Evergreen Forest-->
  
  <!-- Evergreen Forest-->
  <trans start="42" end="43" period="25" prob="10" /> <!-- to Mixed Forest-->

  <!-- Mixed Forest-->
  <trans start="43" end="41" period="25" prob="25" /> <!-- to Decidious Forest-->
  <trans start="43" end="42" period="15" prob="10" /> <!-- to Evergreen Forest-->

  <!-- Shrub Scrub -->
  <trans start="52" end="41" period="25" prob="10" /> <!-- to Deciduous Forest-->

  <!-- Grassland -->
  <trans start="71" end="52" period="15" prob="40" /> <!-- to Shrub/Scrub -->

  <!-- Palustrine Shrub/Scrub-->
  <trans start="92" end="52" period="10" prob="5" />  <!-- to Deciduous Forest-->
  <trans start="92" end="71" period="10" prob="5" />  <!-- to Grassland -->
  <trans start="92" end="91" period="10" prob="10" /> <!-- to Palustrine 
								      Forested -->

</transitions>