GYST is a generalized growth and yield shell developed for the Windows operating system by the Forest Modeling Research Cooperative at Virginia Tech. The purpose of GYST is to provide developers and users of growth and yield models with a readily available interface for implementation of different kinds of models. Users do not need to write tedious user interface code for each new application. Nor are they restricted to accessing one or a few models imbedded in executable code. Instead, users can access growth and yield models by selecting them from a library of models. Models can be added or deleted from the libraries and there are no restrictions placed on how the models have been developed, order of execution within the models, or number, type, and names of variables. Thus, users can insert their own existing growth and yield models as either C or FORTRAN dynamic linked libraries, (DLLs) into the shell for implementation. GYST is useful for a variety of purposes including assessing the performance of alternative models, inventory updating, testing newly developed growth and yield models and archiving and accessing models.

How GYST works
GYST works by linking data to growth and yield models within a spreadsheet environment. Columns are variables passed into and out of DLLs that have been developed and are archived in the library of models. Data (stand- or tree-level variables) are inserted into the cells of the spreadsheet either manually or read in as a delimited ASCII file. Buttons from
the toolbar (such as "Initialize" or "Grow") activate the link between the data and models causing the data to be passed into the models for computation and back out to the spreadsheet.

GYST in a Windows application
GYST has the same basic functionality as other Widows Applications. File functionality includes importing and exporting data, opening and using multiple GYST windows and saving GYST projects. Edit capability includes Windows clipboard access which allows integration with other Windows applications such as graphics packages and word processors. Spreadsheet functionality includes block highlighting, sorting, printing and moving about the cells of the spreadsheet.

What GYST does
GYST can initialize a current stand, grow a stand, or display a stand table. Initializing a stand passes stand variables to the stand-level portion of the DLL for prediction of current conditions. Growing a stand projects stand attributes into the future using the specified stand-level growth algorithm in the DLL. Growth can be accomplished for a desired number of years or to a specified target value of on of the column variables. Output can be obtained at specific intervals. Projections can be made to minimum or maximum values of specified variables. A stand/stock table can be created by passing stand-level variables to the selected stand/stock table portion of the DLL.

Download a Demonstration Version

To download a demonstration version:

  • Click GYST to start downloading.
  • With your web browser select "save this program to disk".
  • Run the file saved in step 2 by double clicking it. The setup utility starts.
  • Run the demo program in the destination directory of step 3.

GYST is available for $350.00. To place an order or obtain additional information, contact

GYST user manual
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