Vegetation Resources Inventory
Forest Inventory Statistical Rigor (Biometrics) Support
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Variable Density Yield Prediction |
Overview
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.
