Executive Summary

As part of the provincial Timber Supply Review, the British Columbia Forest Service has examined the availability of timber in the Arrowsmith Timber Supply Area (TSA). The analysis assesses how forest management practices, that were current when information was collected, 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 Arrowsmith TSA is situated on the southern portion of Vancouver Island in the Duncan and Port Alberni Forest Districts. As well as the Arrowsmith TSA, the forest districts are comprised of 5 Tree Farm Licences (TFLs), Timber Licences, Federal and Provincial Parks and private lands. The Arrowsmith TSA currently provides 8% of the total timber supply from Crown land in the two forest districts.

Since the last timber supply analysis in 1988, the land base for the Arrowsmith TSA has changed due to TSA boundary updates, timber licence reversions, land transfers to the Pacific Rim National Park, and area being transferred from adjacent TFLs to the TSA to meet commitments for the Small Business Forest Enterprise Program (SBFEP).

When the analysis was initiated the allowable annual cut for the Arrowsmith TSA was 498 250 cubic metres per year. The analysis does not assess the timber supply from Woodlot Licences (15 100 cubic metres per year including currently unallocated woodlot AAC) and deciduous stands (4000 cubic metres per year). Therefore, the analysis examines timber supply from a land base currently assigned an AAC of 479 150 cubic metres per year.

In June 1994, the allowable annual cut was temporarily reduced by 16 000 cubic metres to 482 250 cubic metres per year to account for the Clayoquot Sound Land Use decision, and to ensure forest management objectives in the remainder of the TSA were not compromised. Because this was a temporary reduction (Part 15 of the Forest Act), and the land use decision was not finalized when this analysis was initiated, the area to which the temporary reduction applies was included in the land base for this analysis. Therefore the analysis does not assess the implication of the Clayoquot land use decision.

The Arrowsmith TSA covers a total area of about 169 000 hectares, of which approximately 75 000 hectares are considered available for timber harvesting under current management practices. The area is dominated by stands of Douglas­fir, western redcedar and hemlock, with minor proportions of balsam, pine and spruce. Approximately one­half of the timber harvesting land base has sites classified as poor quality for growing timber.

Based on current forest management assumptions, analysis results indicate that, to avoid large rates of decline in subsequent decades, the harvest level must be reduced immediately from the existing AAC by approximately 2%, or 10 150 cubic metres per year, to 469 000 cubic metres per year. After the first decade, the harvest forecast declines from this reduced level by about 10% per decade for 3 decades to reach 346 000 cubic metres per year, 10.1% below the long­term harvest level. This harvest is maintained for 12 decades and then rises to the steady long­term level of 385 000 cubic metres per year. An alternative short­term forecast would be to harvest at the existing AAC for one decade, but afterwards the decline would be faster (12% per decade).

Even if harvesting is reduced immediately to the steady long­term level, it cannot be maintained at that level without causing large timber supply disruptions in the future. Furthermore, the sensitivity analyses indicate that harvests below the long­term level cannot be avoided even if timber yield estimates and management assumptions used in the analysis are assumed to underestimate timber supply.

The most important factor contributing to the decline from the initial harvest level is the magnitude of the area reverting to the timber harvesting land base from Timber Licences. Until the reverted areas reach green­up conditions, they will limit harvesting in adjacent areas. If the Timber Licence reversions were assumed not to limit harvests on adjacent areas the current AAC could be maintained for 10 years. Harvests over the medium term - between decades 4 and 15 - are determined mostly by the large area of stands on poor quality sites (51%) that have relatively older minimum harvestable ages, which delays the availability of second growth for harvesting.

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.

Sensitivity analyses indicate that short­term timber supply is sensitive to changes in existing stand yields, green­up ages, forest cover requirements (cutblock adjacency and visual quality) and the size of the timber harvesting land base. Large reductions in the initial harvest level result from increased green­up ages and more restrictive forest cover requirements for cutblock adjacency.

Long­term timber supply is slightly sensitive to moderate shifts in area between management emphasis zones (forest cover requirements), and is sensitive to changes in land base, green­up ages, managed stand yields and forest cover requirements for visual quality.