Interagency Clearinghouse of Ecological Information


The ILAP team used several tools, all of which are available to the general public and some of which is free. Generally, the team used maps in a geographical information system (GIS) software to summarize initial conditions for broad ecological regions in Oregon and Washington.

The maps used to get a snapshot of current conditions were:

  • Forest composition and structure developed from gradient nearest neighbor (GNN) imputation (available on the Lemma website) and
  • Potential Vegetation Types (PVT) developed by the US Forest Service

The GNN vegetation data was summarized by PVT and then entered into the Vegetation Dynamics Development Tool (VDDT) software, which models how vegetation might change over time given certain assumptions about the typical natural disturbances and growth rates for an ecological region.

The goal here is to provide a way for the general public to analyze their own part of the world. The first step would be to get an idea of initial conditions, either by using the GNN and PVT data to summarize overstory and understory vegetation, or by using personal expertise and local data. The next step would be to enter the initial conditions into the VDDT model for your region, and then run the models for the desired number of years to get a sense of what your part of the world may look like in 10 or 100 or 150 years.

Experienced GIS users may want to download GNN and PVT layers to summarize data. Experienced VDDT users may want to run the models and tweak them based on their own expertise or out of sheer curiosity. People interested in the model results, but who do not feel comfortable with the technology, can go to the Model Products and Publications section of this site.

Vegetation Dynamics Development Tool (VDDT) Models

An explanation of how to download VDDT models from this website and pull them into the VDDT software is provided further down this page. The Access databases that can be brought into a VDDT session are provided below, organized by region. Please keep in mind that while the ILAP team coordinated the regional boundaries with the Lemma team, the GNN Modeling Regions are numbered differently.

All VDDT Access database files are zipped to reduce download times.

Ancillary files that are often used, but are not necessary, when running VDDT.

Ecoclass codes crosswalked to ILAP Potential Vegetation Type

List of standardized codes used throughout the VDDT models

How to Download the Models

(For experienced VDDT users)

Users of the modeling software Vegetation Dynamics Development Tool (VDDT) can download the models developed by the ILAP team. Getting the software is easy and free, although you will need a password to extract the installation program. Go to and register with the VDDT Software Coordinator, who will email the password to you.

Recommended System Requirements for VDDT

  • Microsoft Windows 2000 or later; and
  • 512 MB memory.

Running the ILAP Team’s VDDT Models

  1. Load the Microsoft Access database for a region of interest from the ILAP website onto your own hard drive using directory C:\VDDT\... For example: for Region 4, download the “VDDT_SWO_102408_base.mdb” file as C:\VDDT\VDDT_SWO_102408_base.mdb Alternatively, you can run the models in your own directory as long as you change the pathways in the database table named Project.
  2. Start VDDT by selecting “VDDT” from the “Programs” menu under the “Start” button.
  3. Select “Import” from the “File” menu.
  4. Choose “Project” and then “MDB” from the menus.
  5. A pop-up window “Select VDDT Database” will appear. Go to the “Look In” box to navigate to files. If you loaded the database and attribute files into directory C:\VDDT\COLAIV_sage the pop-up window will navigate there automatically. Select “VDDT_sage.mdb”. Click on “Open”.
  6. In the “Import Projects” table, click on a coded name, and look in the “Description” box for a more complete name. Select a VDDT model, and click “Import”. VDDT will display the associated “Transition Pathway Diagram” for the model. It has been imported but you cannot fully manipulate the model until you open it.
  7. Select “File” and then “Open” and from the “Open Projects” table select the model that you just imported.
  8. Select “Run” and then “Settings” to define your general run conditions. The “General” tab will let you set the “Number of timesteps”, the “Number of cells”, and the “Number of simulations. The “Initial Conditions” tab shows you the “Total Area Represented” and the percentage of this acreage that is in each “Class”.Click “OK” to close the screen.
  9. The classes were defined by the ILAP team. In the example above, Class A is “GF” and “PG”. To find the definitions of these codes close the “Run Settings” window and select “File” then “Properties” then “Definitions”. Selecting the “Cover Types” tab in the “Definitions” pop-up window shows that “GF” stands for “GrassForb” and selecting the “Structure Stages” tab shows that “PG” stands for “PerennialGrass”.
  10. Run the model by selecting “Run” then “Start Model”.
    When the run is complete, you can view your results by clicking on “Run” and then “Graph Results”. For example, in the “Graph Results” pop-up window, select “Classes” from the “Display Variable” box and “Bar” as “Graph Type” and hit “OK” to display the distribution of area by class at up to four different time steps.
  11. To save any changes you made to your VDDT Project, select “File” and then “Save As” and enter a new name for it. If you now go to the “File” and then “Open” menu, you should see your newly-named Project, alongside the original ILAP project.