As part of the provincial Timber Supply Review, the B.C. Forest Service has examined the availability of timber in the Mid Coast Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the next 250 years. It also examines the potential changes in timber supply stemming from uncertainties about forest growth and management actions.
The Mid Coast TSA covers approximately 2.2 million hectares, of which about 156 000 hectares are considered available for timber harvesting under current management practices. The area is dominated by hemlock and redcedar stands.
The current allowable annual cut (AAC) was determined by the Chief Forester in 1992 using the 1990 timber supply analysis and a wide range of other criteria. At that time, the Chief Forester indicated that a further review of timber supply, using new inventory, growth and yield, and operability criteria, would be completed in January 1993. This report documents those results.
The current AAC for the Mid Coast TSA is 1 million cubic metres per year. Thirteen per cent of the current AAC, 130 000 cubic metres per year, is to be harvested from low-quality hemlock, redcedar and balsam stands, which are not included in this analysis. Therefore, the current harvest level assumed for this analysis is 870 000 cubic metres per year.
The analysis results indicate that the timber supply in the Mid Coast TSA is facing an imminent decline. There are two main reasons for this decline:
1. The area considered to be available for timber harvesting in the Mid Coast TSA is approximately 39% smaller than the area indicated in the 1990 timber supply analysis. This change, which is due primarily to revised operability mapping, is by far the most important factor affecting the timber supply forecast.
2. Current management objectives to have forest land provide resource other than timber have been included in the timber supply analysis and therefore limit timber availability.
If the current AAC is maintained for 10 years, the harvest level must decline in the following years by a minimum of 10% per decade to prevent a major shortfall in the future timber supply. This decline is projected to continue until a steady long-term harvest level is reached in approximately 60 years. The steady long-term harvest level is just over 550 000 cubic metres per year, 37% below the current AAC.
Uncertainty in the data or assumptions used in the analysis affect the harvest forecast in one of two ways:
1. The harvest forecast is significantly increased by setting minimum harvest ages to the optimum age in term of timber volume production, by removing all forest cover requirements for old growth/wildlife habitat, or by increasing the estimated growth rate of all forest stands.
2. The harvest forecast is significantly decreased by increasing minimum harvest ages, by increasing minimum green-up ages, by increasing forest cover requirements for non-timber values, or by decreasing the estimated growth rate of all forest stands.
Other changes to the data or assumptions used
in the base case had only small to moderate effects on the harvest
forecast.