Variable Density Yield Projection (VDYP)
The Variable Density Yield Projection (VDYP) program provides yield predictions for unmanaged B.C. stands in inventory and timber supply applications. This complements managed stand yield predictions from Tree and Stand Simulator (TASS) and Table Interpolation Program for Stand Yields (TIPSY).
The first version of VDYP (VDYP 6) was released in 1993 and replaced all earlier versions of natural stand yield prediction systems. This latest version (VDYP 7) represents the culmination of close to a decade (nine years) of research, development, and testing to prepare and fit the model using temporary sample plot (TSP) data (52,000 plots) and permanent sample plot (PSP) data (9,300 plots). Additionally, inventory audit samples (2,700 plots) were used to validate the model.
Although the previous version, VDYP 6, was adequate for its time, a number of limitations were identified. The most significant limitation was that VDYP 6 used crown closure as the measure of stand density. In addition, VDYP 6 did not take advantage of the latest Vegetation Resources Inventory (VRI) ground sample data to make more accurate yield predictions.