The critique first confirms the results of the Forest Service analysis and then examines the implications of changing three of the forecast factors used in Forest Service analysis: using the 'Table Interpolation Program for Stand Yield' (TIPSY), increasing the size of the timber harvesting land base and changing forest cover requirements. The critique reaches the following conclusions:
Using the Table Interpolation Program for Stand Yield (TIPSY)
TIPSY, which estimates volumes from managed forests was not available when the Arrow timber supply analysis was done. Instead, as in other timber supply areas which were analyzed early in the Timber Supply Review, timber volume estimates from unmanaged forests described by the Variable Density Yield Projection (VDYP) were used. Using TIPSY has a major effect on the projected long-term timber supply, raising it approximately 25 to 30 per cent above the VDYP projection used in the Forest Service analysis. The use of TIPSY has no effect on the short-term harvest level.
Increasing the size of the timber harvesting land base
Including the 'problem forest types' and 'environmentally sensitive areas' and reducing the area deleted for roads and landings increases the timber harvesting land base in the Arrow Timber Supply Area by 10 per cent compared to the land base used in the Forest Service analysis. Consequently, timber harvesting in both the short and long term is projected to increase relative to the Forest Service base case.
Changing forest cover requirements
The forest cover requirements used in the Forest Service analysis are based primarily on 1992 guidelines. The technical critique contends that its assumed forest cover requirements are more stringent than those used in the Forest Service analysis and more representative of operational realities in 1994. The effect of this change on the short-term timber supply is noticeable--the projected initial harvest level is 557,000 cubic metres per year (if the Forest Service analysis land base is used).
Based on these findings, the critique projects the current allowable annual cut of 619,000 cubic metres can be maintained for 50 years. Periodic timber supply reductions are projected 60, 80 and 120 years from now, with a subsequent increase to a long-term sustainable level of approximately 650,000 cubic metres in 150 years.
The critique concludes that future timber supply analyses will require improved land base definition to reflect current integrated resource management, local managed timber yield information and more reliable estimates of site productivity in old and very young forests. The critique recommends development of reliable and predictable rules for forest allocation to improve the Forest Service analysis model.
