As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Okanagan 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 the 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 their associated uncertainty. The forecasts are to be used for discussion purposes only; they do not imply any particular allowable annual cut (AAC) recommendations.
The Okanagan TSA covers approximately 2.17 million hectares, of which about 1.04 million hectares are considered available for timber harvesting under current management practices. The present AAC for the Okanagan TSA is 2.615 million cubic metres per year. The entire AAC for the Okanagan TSA is fully allocated among its three forest districts - Salmon Arm, Vernon and Penticton.
While much of the Okanagan TSA is managed for integrated resource activity, approximately 53% of the land base is assigned special management requirements to account for wildlife habitat, community watersheds, visual quality, selection harvesting, and areas deferred from harvesting under approved Local Resource Use Planning.
Given current management assumptions, the analysis shows that the present AAC of 2 615 000 cubic metres per year can be maintained for another 20 years without causing a sharp drop in future harvest levels. Beginning in 20 years harvests decrease by 10% per decade until the long-term harvest level of 2 022 000 cubic metres per year is reached in 40 years.
Although the present AAC can be maintained for another 20 years, the mountain pine beetle epidemic in the southern portion of the Okanagan TSA has resulted in a temporary increase of 189 000 cubic metres per year to the AAC. The temporary AAC is now 2 804 000 cubic metres per year. The temporary AAC can only be maintained for 10 years followed by declines at the beginning of the second and third decade to the long-term harvest level 30 years from now.
Many of the data and assumptions used in the analysis are subject to varying degrees of uncertainty. Sensitivity analysis was used to determine how the data and assumptions impact the results of the timber supply analysis. Short-term timber supply is primarily sensitive to volume estimates for existing stands and forest cover requirements. Higher yield estimates for existing stands permit the present AAC to be maintained for 60 years while lower existing stand yield estimates require a 30% drop in initial harvest rates. Relaxing the forest cover requirements permit the present AAC to be maintained for up to 40 years while tighter forest cover requirements cause the initial harvest rate to decline by 6%. Changes in regenerated stand yields have no impact on short-term harvest rates although the long-term harvest is significantly affected.