As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Williams Lake 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. 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 Williams Lake TSA covers a total area of approximately 4.87 million hectares, of which about 1.66 million hectares are considered available for timber harvesting under current management practices. The current AAC for the Williams Lake TSA is 3.975 million cubic metres per year. It is administered by three forest districts - Chilcotin, Williams Lake, and Horsefly and is split into four components: conventional conifer sawlog, deciduous stands, three western supply blocks, and mountain pine beetle salvage. The conventional sawlog (referred to as the "main TSA" in this report) and the three western supply blocks are the focus of this report.
The TSA has a variety of management regimes, ranging from areas where timber harvesting is excluded to areas where all resource interests are integrated. Approximately 20% of the timber harvesting land base is managed with an emphasis on non-timber resources such as wildlife habitat and aesthetics. The other 80% is managed as integrated resource areas. To account for these values, forest cover objectives have been applied to the various management areas. About 21% of the TSA is dry-belt Douglas-fir that is harvested under a selection management regime.
The base harvest forecast for the main TSA uses a starting harvest level of 2 670 000 cubic metres per year to reflect the conventional sawlog component and a temporary increase for mountain pine beetle salvage. This level results in the harvest forecast falling below the long-term harvest level for 4 decades (decades 4 through 7). The long-term harvest level, about 20% below the starting harvest level, is reached in decade 8.
Given the mountain pine beetle infestation, the harvesting history in this TSA, and current management assumptions, it is not possible to forecast a harvest flow that does not fall below the long-term harvest level. Any harvest forecasts without this shortfall would result in an acute shortage of available timber in the future. Attempts to minimize this shortfall result in a harvest forecast that starts slightly below the long-term harvest level. After 7 decades, the harvest increases to the long-term harvest level of 2 111 000 cubic metres per year.
Three important factors contribute to the shortage of timber shown in the harvest forecast for the Williams Lake TSA:
-the extensive mountain pine beetle infestation that occurred in the 1970s and 1980s;-the re-classification of the stands in a large portion of the TSA, which changed the stand age distribution and increased the number of low quality stands; and-the decline in the timber harvesting land base by almost 400 000 hectares from that assumed in the 1988 timber supply analysis.
The reasons for the decline include:
The results of the analysis of the three western supply blocks indicate that, given current management assumptions, an initial harvest of 425 000 cubic metres per year is possible. The harvest level then falls 16% over the next 2 decades to the long-term harvest level of 358 000 cubic metres per year. Starting the harvest forecast at any higher level results in shortages of available timber in the future.
Many of the data and assumptions used in the Timber Supply Review are subject to varying degrees of uncertainty. Sensitivity analysis was used to examine how uncertainty about data and assumptions affects the results of the analysis. It showed that the timber supply for the main area of the TSA is particularly sensitive, in the first 8 decades, to reductions in the timber harvesting land base, 20-year increases in minimum harvest ages, application of old-growth forest cover guidelines, decreases to the existing stand volume estimates, and changes in the adjacency forest cover guidelines.
Harvest levels over this same period are moderately sensitive to increases in the existing stand volume estimates, changes in the regenerated stand volume estimates, the length of time it takes for stands to grow 3 metres tall, and increases in the timber harvesting land base.
The long-term harvest level is highly sensitive
to increases in the timber harvesting land base, changes to volume
estimates for regenerated stands, and application of the old-growth
forest cover guidelines.