As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Kispiox 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 Kispiox TSA available for timber harvesting under current management practices is about 318 000 hectares out of a total land base of approximately 1 223 000 hectares. The total volume of standing timber on the timber harvesting land base is about 85 million cubic metres, of which 81 million cubic metres (approximately 95%) is currently above minimum harvestable age. The forest on the timber harvesting land base is composed of stands of hemlock (47%), balsam (31%), spruce (12%) and lodgepole pine (8%).
The current AAC for the Kispiox TSA is 1 100 000 cubic metres per year. Under current forest management assumptions, the analysis results indicate that the current harvest level can be maintained for 4 decades without causing a drop in future harvest levels below the longterm harvest level. Beginning in the fifth decade, the harvest level would have to decline by 10% per decade until the longterm level of 630 000 cubic metres per year is reached in decade 10. This harvest projection is referred to as the base case throughout this report.
The above base case 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 on the base case harvest forecast observed in the analysis is due to uncertainty in the volume estimates for existing stands. If existing stand volumes are overestimated by as much as 20%, the initial harvest level must decrease immediately by 10% and continue decreasing by 10% per decade to avoid serious shortfalls in the future. Conversely, if existing stand volumes are underestimated by as much as 20%, then the current harvest level can be maintained for 8 decades before beginning the transition to the longterm harvest level.
While there is no evidence to suggest that existing stand volumes are different from those used in the analysis, there is considerable difficulty accessing the northern portion of the Kispiox TSA. The analysis indicates that if this area, comprising 24% of the Kispiox TSA, is excluded from the timber harvesting land base, harvest levels must decrease immediately to 1 000 000 cubic metres per year and continue decreasing by 10% per decade until a longterm level of 500 000 cubic metres per year is reached.
Site productivity is a key determinant of the expected rate of growth of trees on a site and thus affects greenup ages, minimum harvestable ages and regenerated stand volumes. To approximate the effects of uncertainty in site productivity estimates, sensitivity analysis was conducted in which minimum harvestable ages were changed by 20 years, greenup ages were changed by 5 years, and regenerated stand volumes were changed by 20%. This sensitivity analysis shows that uncertainty in site productivity estimates has significant impacts on medium and longterm harvest levels. If site productivity is lower than estimated, the initial harvest level can still be maintained for 2 decades due to the large amount of older stands currently available for harvest in the Kispiox TSA. The longterm harvest level, however, will be 21% lower than in the base case. If site productivity is higher than estimated, then the harvest forecast is similar to the base case except that the longterm level is 21% higher and is attained 2 decades earlier.
Uncertainty in the amount of forest cover required to meet visual quality objectives has little medium and longterm impacts on the base case harvest flow projections. Under more restrictive visual quality requirements, the current harvest level can still be maintained for 30 years before the transition to slightly lower longterm levels. Under less restrictive visual quality requirements, the current harvest level can be maintained one more decade, than in the base case and the longterm harvest level can be increased by 5%.
Further sensitivity analyses examined the timber supply implications of uncertainty in hydrological greenup heights, oldgrowth forest cover requirements, and adjacency objectives. The greenup height sensitivity analysis shows that timber supply is unaffected if the height requirement for hydrologic greenup is assumed to be 10 metres rather than 6 metres. The oldgrowth forest cover requirement sensitivity analysis shows that if 6% of the timber harvesting land base is required to be covered by forest greater than 200 years old, the current harvest level must start declining one decade earlier to a level 5% lower than in the base case. The adjacency sensitivity analysis shows that if a 4pass or a 5pass harvesting system is required to meet adjacency objectives, the harvest forecast is unaffected. However, if 6 passes are required to meet adjacency objectives, then the initial harvest level must decrease to 1 000 000 cubic metres per year. This level can be maintained for 40 years before declining to a slightly lower longterm level than in the base case.
In conclusion, this analysis indicates that
using current forest management, inventory and growth and yield
information, the current harvest level can be maintained for the
next 40 years. Several uncertainties important to timber
supply can affect this projection. The greatest impact on shortterm
timber supply arises from uncertainty about existing stand volumes
and uncertainty about access to the northern portion of the Kispiox TSA.