As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Mackenzie Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over both the short (next 20 years) and long (next 250 years) term. It also examines the potential changes in timber supply stemming from uncertainties about forest growth and management actions. It is important to note that the various harvest forecasts included in the report indicate only the timber supply implications of current practices and uncertainty. As such, the forecasts should be used for discussion purposes only; they are not allowable annual cut (AAC) recommendations.
The Mackenzie TSA covers a total of about 6.13 million hectares of land and water around Williston Lake in the northcentral area of British Columbia. About 1.16 million hectares of the area are considered available for timber harvesting and production under current management practices. Lodgepole pine, white and Engelmann spruce, and subalpine fir are the tree species most commonly used by the forest industry in the area.
The results of this timber supply analysis suggest that the current harvest level in the Mackenzie TSA (2.951 million cubic metres per year) can be maintained for up to 30 years without creating severe future timber shortages, if followed by a reduction in the harvest level over the subsequent 20year period to about 2.64 million cubic metres per year. Harvests could then increase to 2.81 million cubic metres per year - a level sustainable over the long term - about 100 years from now.
The above results reflect current knowledge and information on forest inventory, growth, and management. However, it is important to recognize that uncertainty exists about several factors important in defining timber supply. A series of sensitivity analyses showed that these uncertainties can affect timber supply to varying degrees.
The uncertainties with the largest potential effects on projected harvests over the next 100 years (that is, greater than 5% cumulative change over the next 100 years compared to the base case results described above) involve estimates of timber volumes in existing stands, the size of the timber harvesting land base, and minimum harvestable ages. An inventory audit completed in 1994 indicated that, for the Mackenzie TSA as a whole, current inventory information together with the timber yield estimation model used for this analysis produced accurate estimates of existing stand volumes. The size of the timber harvesting land base is uncertain mostly due to uncertainty about both the classification of physical operability, and the amount of land to be reserved from timber harvesting to protect environmental values. At this time there is no conclusive information to suggest that the timber harvesting land base is either larger or smaller than defined in the analysis. Until operability limits and environmental protection needs have received further assessment throughout the Mackenzie TSA, the current estimate of the area suitable for timber harvesting constitutes the best available information.
Factors with moderate effects on timber supply over the next 100 years (from 1% to 5% change relative to the base case) include estimates of: site productivity of future managed stands, especially if estimates used in this analysis underestimate actual productivity; regeneration delay, particularly if actual delays are substantially shorter than assumed in the base case; forest cover requirements for management of visual quality, watershed protection, and wildlife habitat when considered cumulatively; forest cover requirements for old-age forest to maintain wildlife habitat; and finally, the minimum age at which stands are assumed to attain oldage characteristics.
Uncertainty about forest cover requirements to maintain visual quality, and the age at which stands reach greenup conditions have a small effect on projected harvests over the next 100 years (less than 1% cumulatively compared to the base case).
The forest inventory and management factors discussed above could affect timber supply over the next 100 years, but uncertainties about these factors would not require reduced harvests over the short term, that is, the next 20 years. The only management uncertainty that could require shortterm harvest reductions is related to forest cover requirements in integrated resource management areas. Specifically, application of a 5pass harvesting system in the integrated resource management areas, rather than the 3pass system assumed for the base case, would require significant harvest reductions from 11 to 20 years from now, to avoid violating forest cover objectives. Alternatively, the same objective could be met by an immediate but smaller reduction to a steady level over the next 20 years. Analysis showed that uncertainties about other factors can affect cumulative timber supply over the next 100 years, but would not require that harvests drop below base case levels over the next 20 years to avoid either violating cover requirements, or creating severe timber supply disruptions in the future.
Over the long term, that is during the period from 100 to 250 years from now, only site productivity of future stands and the size of the timber harvesting land base have large effects on timber supply. Uncertainty about regeneration delay, forest cover objectives for oldage forest for wildlife habitat, and estimates of the minimum age used to define oldage forest all have moderate effects on longterm harvest levels. Minimum harvestable ages, forest cover requirements for visual quality, greenup ages, adjacency objectives for integrated resources management areas, and estimates of timber volumes in existing stands have little to no effect on longterm timber supply.
In conclusion, this analysis indicates that
using current inventory and growth and yield information, timber
harvests in the Mackenzie TSA can be maintained at the current
allowable level for the next 30 years. Several factors related
to the current forest inventory and management regime could affect
timber supply over the next 100 years. No conclusive evidence
was available prior to completion of this analysis to suggest
that significant inaccuracies exist in the information used.