Forest industry input maintains the Variable Density Yield Prediction model overestimates volume in stands 150 years and older and underestimates volume in stands 70 to 120 years old. The comments are based on a study done by a consultant comparing the Variable Density Yield Prediction model estimates to actual permanent and temporary sample plot volumes. The shape of the curves developed from the Variable Density Yield Prediction model estimates usually results in much higher culmination ages than would be indicated by curves with a shape that fits the data better.
Another forest industry submission expresses concern the Variable Density Yield Prediction model does not predict declines in stand volumes past the age of 150. The author has observed stands start losing volume after that age. Since the Prince George Timber Supply Area contains significant amounts of pine types over 100 years old, for which the timber supply projections give no information as to the expected harvest ages, the author asks whether this might impact timber supply projections.
One respondent states it appears the managed stand yields forecast by the Table Interpolation Program for Stand Yields model—on which the long-term harvest level is highly dependent—will only be achieved at the expense of other forest values, i.e. through intensive management for timber values only.
Another forest industry submission asserts substantially increased growth rates are being achieved as a result of basic silviculture practices and further increases will be seen from intensive silviculture treatments under the Forest Renewal Plan. Another important aspect of this faster growth rate is that green-up periods between harvest passes will be shorter than predicted.
One respondent writes that the most detailed study of regenerated stands in the Interior indicates timber supply in regenerated stands is much lower than in natural stands.
