Executive Summary

As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Cassiar Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the next 400 years. 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 Cassiar TSA covers a total area of 13.4 million hectares, of which 394 000 hectares are considered available for timber harvesting under current management practices. The current timber harvesting land base is more than three times larger than that which was reported in the last timber supply analysis in 1984. This increase is the result of more land being accessible and hemlock, balsam and poor site pine stands being included.

The current AAC for the Cassiar TSA is 140 000 cubic metres per year. Although harvest levels have been well below the AAC in the past, they have been rising in recent years.

Given current management assumptions, the analysis results indicate that the initial harvest level can be increased substantially above the current AAC to 842 400 cubic metres per year. This rate of harvest can be maintained for 7 decades before increasing to a long­term harvest level of 867 400 cubic metres per year.

Many of the data and assumptions used in the analysis are subject to varying degrees of uncertainty. Cassiar Forest District staff feel that the extent of the land base assumed to be available for timber harvesting is particularly uncertain. Sensitivity analyses show that timber supply is highly sensitive, both in the short and long term, to changes in the timber harvesting land base.

Given the limited harvesting and silvicultural history of the Cassiar TSA, there is uncertainty about the reliability of the forest inventory and the existing and managed stand timber yield estimates. The harvest forecast is highly sensitive, in the short term, to decreases in existing stand yield estimates. In the long term, the harvest forecast is moderately sensitive to uncertainty in existing yield estimates. Conversely, timber supply has little sensitivity in the short term to uncertainty in regenerated stand yields, but high sensitivity in the long term.

The harvest forecast is highly sensitive to a combination of increasing the timber harvesting land base by 30% and increasing both the existing and managed stand yield estimates by 10%. However, the harvest forecast was only moderately sensitive to the combined impact of a 30% decrease in the land base and 10% decreases in yield estimates.

Two other uncertainties which may affect future harvest levels are estimates of cutblock adjacency requirements and minimum harvestable ages. The harvest forecast is highly sensitive in the short term to increased cutblock adjacency requirements and moderately sensitive to large (20 year) increases in minimum harvestable ages. The harvest forecast is only slightly affected when cutblock adjacency requirements are removed and minimum harvestable ages are decreased.

Uncertainty in green-up ages has a moderate effect on potential harvest levels in the short term, and only a slight effect in the long term.

The main conclusion drawn from the sensitivity analyses is that inventory and mapping work is needed to assist in defining the timber harvesting land base. Timber supply is also sensitive to uncertainties in other variables, such as timber volume estimates. However, more experience in harvesting timber will be needed to indicate the nature and magnitude of these uncertainties in the Cassiar TSA.

In conclusion, this analysis indicates that timber supply in the Cassiar TSA is sufficient to support some increase in harvests above the current AAC. However, the high uncertainties about variables important in determining timber supply should be considered during discussions about future allowable harvest levels.