As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Lakes Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the 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 area of the Lakes TSA available for timber harvesting under current management practices is about 634 000 hectares of a total land base of about 1 123 000 hectares. The total volume of standing timber in the area is about 143 million cubic metres, of which 118 million cubic metres or 83% is currently above minimum harvestable age. The present forest structure has 69% of the stands possessing an age in excess of 100 years. The timber harvesting land base is composed of lodgepole pine (77%), spruce (21%) and balsam (2%).
The current AAC for the Lakes TSA is 1 500 000 cubic metres per year. Under current forest management assumptions, the analysis results indicate that the current harvest level can be maintained for 7 decades. In the eighth decade a 10% decline is projected followed by a 3% decline to a harvest level of 1 310 000 cubic metres per year. A rise to the longterm harvest level of 1 441 000 cubic metres will occur in decade 18. Timber harvesting is expected to have a relatively long transition from harvesting existing timber to harvesting predominantly second growth due to forest cover guidelines. The cover guidelines require a percentage of forest cover to be maintained in ages over 100 years and cause a slower rate of access to the standing inventory in some zones than in the integrated resources management zone.
The analysis has shown that the initial harvest rate could be raised without incurring large timber shortages or violating current management assumptions. An alternative harvest forecast is identified which begins at 1 650 000 cubic metres per year with a decline in the sixth decade to the current harvest level of 1 500 000 cubic metres per year followed in the seventh decade by a further decline of 10% to 1 350 000 cubic metres. A 3% decline would be required in decade 8 to a harvest level of 1 310 000 cubic metres per year. Raising the initial harvest level does not jeopardize the rise to the longterm harvest level in decade 18.
The harvest level cannot be maintained at or above the longterm harvest level, even if it is immediately reduced to the steady longterm level.
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 largest impact observed in the analysis is due to uncertainty in site index for regenerated pine stands. Recent studies in the Lakes TSA and the Morice TSA have shown that the site index for existing pine stands underestimates the growth potential of regenerated pine. It appears that by controlling the number of trees per hectare, a higher growth rate can be achieved. The impact of this is cumulative as faster growth enables trees to produce higher volumes at younger ages and increases the rate of access to the zones where harvesting activity is constrained by the amount of area that may be below the greenup age. The estimated greenup age is lowered by up to 4 years in the caribou corridor and visual quality objective (VQO) zones. The resulting initial harvest level after adjustments have been made is 25% higher than the current harvest level and a further 14% increase in harvest level occurs in decade 18.
Timber supply is quite robust to all sensitivity analysis over the next 20 years. Moderate increases in the current harvest level may also be achieved if either existing volumes are being underestimated or if visual quality objectives can be met with less restrictive forest cover guidelines.
Moderate extensions of the current harvest level beyond the base case may be achieved if stands become merchantable 10 years earlier, if the timber harvesting land base increases or if greenup ages are in fact lower, as a faster rate of access in the caribou corridor and VQO zones can occur.
The analysis does show that moderate impacts in longterm timber supply may require the harvest level to decline 23 decades earlier than in the base
case or require a deeper dip below the longterm harvest level to avoid serious timber supply shortfalls. Uncertainties which show this trend are the uncertainty in existing stand volume estimates, the uncertainty about oldgrowth requirements, the uncertainty in the size of the timber harvesting land base and the uncertainty in the greenup age required to meet adjacency constraints.
In conclusion, this analysis indicates that
using current inventory and growth and yield information, the
current harvest level can be maintained safely for the next 20 years
without jeopardizing future opportunities in forest management.
Several uncertainties important to timber supply produce moderate
impacts which will deserve further discussion in the future.
However the opportunities produced by high growth rates in managed
pine stands provide a great deal of flexibility in the harvest
level and may completely offset any negative impacts on timber
supply due to other uncertainties. It will be important to determine
if the growth response that has been observed to date will continue.