As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Invermere 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 Invermere TSA covers a total area of about 1 018 000 hectares, of which about 234 000 hectares are considered available for timber harvesting under current management practices. The area is dominated by stands of lodgepole pine, Douglasfir and spruce. The current AAC for the Invermere TSA is 650 564 cubic metres per year. This does not include 6700 cubic metres apportioned to woodlot licences.
The results of this timber supply analysis suggest that the current harvest level must be reduced immediately by about 12.7% or 82 564 cubic metres to 568 000 cubic metres per year in order to avoid either the need for more rapid harvest reductions over the next few decades, or significant shortfalls in timber supply further in the future. To continue to avoid major harvest shortfalls, harvests must decline from this initial harvest level by about 12% per decade over the next 5 decades to a low of about 315 000 cubic metres per year, which is 12.5% below the steady longterm harvest level. In about 90110 years, when timber harvesting is projected to occur predominantly in secondgrowth stands, the harvest level could increase to the steady longterm harvest level of about 360 000 cubic metres per year.
Several factors contribute to the need to reduce harvests from the currently approved level. The most important factor is that the current harvest level is well above the steady, longterm harvest level. In this situation harvest rates must decline toward the longterm level to avoid serious timber supply shortfalls in the future. Also contributing to the decline, to some extent, are forest cover requirements for forest resources such as wildlife habitat, scenic quality, biodiversity and community watersheds. However, even if these forest cover requirements were removed, harvests would still need to decline in the near future. An additional contributing factor is that significantly less area is available for timber harvesting today than when the last timber supply analysis was completed in 1981. Riparian buffers to protect stream and lake ecosystems, forest ecosystem networks and steep slope sites below the operability line, all areas previously considered available for harvesting, now are not available under current standards of practice.
The above results reflect current knowledge and information on forest inventory and growth. However, it is important to recognize that uncertainty exists about several of the factors that define timber supply. A series of sensitivity analyses indicate that these uncertainties can affect timber supply to varying degrees.
The shortterm timber supply is particularly sensitive to yield estimates for existing stands, land base size, forest cover requirements (especially for ungulate winter range), large increases to oldgrowth requirements, and unsalvaged losses. Minimum harvestable ages, and length of greenup periods are factors that also affect shortterm timber supply, but to a lesser degree.
The longterm harvest level is highly sensitive to uncertainty in yield estimates for regenerated stands, the size of the timber harvesting land base and unsalvaged losses. The longterm harvest level is lightly impacted by uncertainty in minimum harvestable ages, length of greenup periods, greenup forest cover requirements, and oldgrowth requirements.
The need to harvest below the longterm level between decades 5 and 9 can be emphasized or reduced by changes to any of the following factors: initial harvest level and rate of decline, size of the timber harvesting land base, minimum harvestable ages, estimates of existing stand yields, length of greenup periods, and greenup forest cover requirements. The choice of starting harvest rate and rate of decline may also change the harvest level during this time.
In conclusion, this analysis indicates that using current inventory
and growth and yield information, timber harvests in the Invermere TSA
must drop over the next few decades even if inventory, growth
and yield and management assumptions used in this analysis significantly
underestimate timber supply. It will be important to examine
forest cover guidelines, especially for ungulate winter range
and visual quality objectives when deciding on a strategy for
the transition from the current harvest level to a level sustainable
over the long term.