As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Soo Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the next 250 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 harvest forecasts in this 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 total area of the Soo TSA is about 880 000 hectares of which 106 000 hectares are considered available for timber harvesting under current management practices. The total volume of standing timber in the area is about 30 million cubic metres, of which 24 million cubic metres is of merchantable age. The area is dominated by stands of Douglas-fir, western hemlock and amabilis fir, with smaller proportions of western redcedar.
In January 1992, the AAC for the Soo TSA was reduced from 697 600 cubic metres to the current AAC of 580 000 cubic metres.
Given current management assumptions, this analysis shows that the AAC cannot be maintained without causing a sharp drop in future harvest levels below the long-term yield. The harvest flow selected as the base case indicates a harvest reduced immediately by 13%, to a harvest level of 506 000 cubic metres per year for a decade, followed by a reduction of 12% per decade for 2 decades to reach a level of 394 000 cubic metres, 11% below the long-term level. This harvest is maintained in decades 3 to 7 and then rises to the steady longterm level of 442 000 cubic metres.
In the Soo TSA the original abundance of mature forest which historically allowed harvest rates well above the long-term level no longer exists. The 1992 AAC reduction was the first step in the decline towards the long-term level. To avoid major timber shortfalls below the long-term level in the future, the remaining mature timber must be harvested at a rate which allows the existing young stands to reach harvestable ages and volumes.
The harvest forecast is extremely sensitive to the estimate of minimum harvestable age because of the age class structure. The ages were based on wood-product objectives and are slightly higher than those used in other south coastal TSAs. Decreasing the ages by 10 years produces a forecast that declines immediately by 6% then steps down 6% per decade to reach the long-term level in decade 4.
The short-term forecast is also very sensitive to uncertainty in the two main factors which affect existing volumes of mature timber - existing stand yields and the size of the timber harvesting land base. Squamish Forest District staff are concerned that the yields from the remaining poor stands may be lower than indicated by the yield curves, especially in the Pemberton Supply block where (there is a high incidence of decay). Also, decreases in the accessible land base are a concern where access is blocked by private land.
The long-term harvest forecast is highly sensitive to uncertainty about regenerated stand yields and the size of the timber harvesting land base, but is generally not sensitive to uncertainty about other data and assumptions.
The forest cover requirements for forest resources
such as wildlife, water quality and visual quality impact timber
supply slightly in both the short and long term, but even if these
requirements are removed, the harvest forecast still shows a decline
in the future.