As part of the provincial Timber Supply Review, the B.C. Forest Service has examined the availability of timber in the Revelstoke Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the next 200 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 only indicate the timber-supply implications of current practices and uncertainty. As such, the forecasts should be used for discussion purposes only; they are not intended to imply any particular AAC recommendations.
The Revelstoke TSA covers a total area of 504 000 hectares, of which about 63 000 hectares are considered available for timber harvesting under current management practices. The area is dominated by balsam and spruce mixtures, hemlock and cedar stands. The current allowable annual cut (AAC) for the TSA is 269 000 cubic metres per year.
Given current management assumptions, the analysis shows the current AAC cannot be maintained without causing a sharp drop in future harvest levels below the long-term level. The maximum harvest over the first decade is 254 000 cubic metres per year, 5.6 % below the current AAC. Then, beginning in the second decade, harvests must decrease 12% per decade until the long-term harvest level of 98 000 cubic metres per year is reached 80 years form now.
Initial harvest levels greater than 254 000 cubic metres per year or rates of decline less than 12% per decade result in harvests falling significantly below the long term level, usually around 100 years from now. Conversely, if slower rates of decline are desired the initial harvest must drop below 254 000 cubic metres per year. Given current management assumptions, future decreases in harvest levels can only be avoided by decreasing the initial harvest rate by over 60% to the long-term harvest level of 98 000 cubic metres per year. Sustained harvesting at this rate maintains significantly higher growing stock volumes and higher harvest ages than for the forecast that starts with a harvest of 254 000 cubic metres per year.
Many of the data and assumptions used in the analysis are subject to varying degrees of uncertainty. Revelstoke forest district staff feel in particular that the volumes for existing stands used in the analysis may be optimistic and the forest cover requirements for the timber zone may not be tight enough. They also believe that the regenerated yields used in this analysis may be too low and as a result the long-term harvest level under-estimated. Sensitivity analysis was used to examine how uncertainty about these and other data and assumptions impact the results of the timber supply analysis.
In the short term, harvest levels are very sensitive to decreased yield estimates for existing stands and to tightening of forest cover requirements, which account for non-timber values such as visual quality, wildlife and old-growth.
Short-term harvest levels are moderately sensitive to increases in yield estimates for existing stands, relaxation of forest cover requirements, changes in green-up periods, and minimum harvest ages. Uncertainty about yields for regenerated stands has very little impact on short-term harvest levels.
The long-term harvest level is highly
sensitive to uncertainty about regenerated yields but in general
the long-term harvest level is not very sensitive to uncertainty
about other data and assumptions.