As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Cranbrook 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 Cranbrook TSA covers a total area of 1.48 million hectares, including 45 000 hectares of park land not accounted for in the inventory file (i.e. Purcell Wilderness Conservancy, Elk Lakes Provincial Park, Elk Lakes Recreation Area, Top of the World Park and Akamina Kishinena Recreation Area). About 423 445 hectares of the Cranbrook TSA are available for timber harvesting under current management practices. Total current volume of operable standing timber in the area is about 54 million cubic metres, of which 44 million cubic metres are of harvestable age. The area is dominated by lodgepole pine and spruce stands with lesser amounts of Douglasfir, larch, balsam, cedar, and hemlock stands.
For the purpose of this analysis, the AAC is assumed to be 896 136 cubic metres per year. This assumption is required as the land base from the former Tree Farm Licence (TFL) 13 is now included in the Cranbrook TSA. The former TFL 13 AAC of 27 200 cubic metres has, therefore, been added to the approved Cranbrook TSA AAC of 873 810 cubic metres for analysis purposes. The assumed AAC of 896 136 cubic metres does not include 4874 cubic metres that is apportioned to woodlots.
Current forest management of the Cranbrook TSA includes recognizing areas with significant forest resource values such as aesthetics, wildlife, community water supply, and old growth. Range values are also accounted for in the analysis. Resource values have been accounted for by excluding some sensitive areas and applying forest cover requirements to the land base that is assumed to be available for timber harvesting and range.
Given current management assumptions, the analysis shows the assumed AAC of 896 136 cubic metres per year cannot be maintained without causing significant reductions in future harvest levels below the longterm level. The report projects that the harvest rate may have to decline by 10% immediately, then by a further 31% over the next 5 decades to 559 000 cubic metres annually. After a further 7 decades, the harvest could then rise to the longterm harvest level of about 633 000 cubic metres per year. The longterm harvest level is sustainable over the long term given current management assumptions.
Many of the data and assumptions used in the analysis are subject to varying degrees of uncertainty. As an example, the extent of the land base assumed available for timber harvesting is particularly uncertain due to potential changes in management guidelines, or through technical innovations.
Sensitivity analysis was used to examine how uncertainty about data and assumptions affect the results of the timber supply analysis.
Over the first 8 to 10 decades
harvest levels are most sensitive to changes in requirements for
the maintenance of old growth, more stringent forest cover requirements
to account for nontimber values and changes to volume estimates
for existing timber. Shortterm harvest levels are also moderately
sensitive to changes in minimum harvestable ages but are relatively
insensitive to changes in yield estimates of future regenerated
stands. The longterm harvest level is sensitive to uncertainty
of regenerated stand yields and the land base assumed available
for harvesting. In general, the longterm harvest level is
not sensitive to uncertainty about other data and assumptions.