As part of the provincial Timber Supply Review, the B.C. Forest Service has examined the availability of timber in the northern portion of the Kalum Timber Supply Area (Kalum North). 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 timber supply stemming from uncertainties about forest growth and management actions.
Kalum North covers a total of 1.665 million hectares, of which about 238 000 hectares are considered available for timber harvesting under current management practices. The area is dominated by old-age balsam and hemlock forests. The portion of the allowable annual cut (AAC) currently administered in Kalum North is 1.25 million cubic metres.
The results of the analysis show that under current management practices, the current harvest can be maintained for one decade. However, after the first decade, the timber harvest declines by about 10% per decade over the next 120 years to a level of 385 000 cubic metres per year. This rate of decline is necessary to avoid harvests falling below the long-run level 110-140 years from now. This long-run level is one-third of the current harvest. Even if forest management could increase expected timber growth by 50%, the revised long-run sustainable harvest would be limited to one-half of the current harvest. Further, analysis of uncertainties in data indicates that this assessment of timber availability may be optimistic, at least for the next few decades.
The analysis shows that potential harvest levels for the next three decades are affected substantially by changes in estimates of: existing mature timber volumes; minimum harvest ages for second-growth stands; number of harvesting passes (that is, guidelines affecting timing of harvests in stands adjacent to recently cut areas); and the area considered available for timber harvesting.
On the other hand, short-term harvests are not affected greatly by changes in: estimated volume yields of second-growth stands; timing of access to the currently inaccessible northeastern portion of Kalum North (Upper Nass drainage); the age a harvested area must reach before the adjacent block can be harvested (green-up age); or regeneration delay.
Estimates of minimum harvest ages for second-growth stands can be particularly important for defining short-term harvests. This is because the sooner new stands are ready to harvest, the more quickly existing stands can be harvested. The analysis shows that reducing minimum harvest ages allows the current harvest level to be maintained for two rather than only one decade. Although timber volumes, which largely determine timing of harvests in second growth, can be estimated from similar areas, these volumes are still uncertain because there are currently few second-growth stands over 20 years old in Kalum North from which to estimate yields. Further, future markets and harvesting economics are unknown. It may be premature to increase or prolong current harvests based on optimistic estimates of when second growth will be available.
Estimates of volume in existing mature stands also affect short-term harvesting possibilities. Kalum Forest District staff believe that volumes in existing mature stands may be overestimated by 10%. If this is true, an immediate decrease of about 5% in the current harvest would be required to maintain a 10% rate of decline from the current to the long-run harvest level without experiencing a timber shortage between 110 and 130 years from now. Also, a lower estimate of volumes in existing stands counteracts the potential increase in near-term harvests afforded by reducing minimum harvest ages.
This analysis employs an estimate of the area required to help protect biological diversity through forest ecosystem representation. Environmentally sensitive areas, streamside buffers, integrated management plan areas, and some non-merchantable and inoperable areas contain representative forests. Some additional area is also required to protect 12% of the major forest ecosystems across the landscape with minimum fragmentation. The methods used to determine the additional area required to protect biological diversity reflect current practice, although more experience in managing for these values is needed to increase the certainty of estimates. Any changes in the area set aside in representative ecosystems would affect the land base available for harvesting, and therefore timber availability over the next three decades.
Establishment of new tree crops after logging has been difficult in some areas of Kalum North, specifically the Bell Irving drainage in the north. While regeneration delay estimates used in this analysis reflect current standards, it is possible that regeneration delays may actually be longer in this drainage. The analysis showed that regeneration delay did not significantly affect short-term timber availability. However, regeneration delay does reduce available timber supply 20-30 years into the future if guidelines stipulating harvest timing in adjacent areas are made slightly more stringent than current practice (allowing a maximum of 33% rather than 40% of the area to be in a disturbed state; that is, younger than green-up age).
Overall, uncertainties in data used to describe current forest management indicate that short-term timber availability is more likely overestimated than underestimated in the base case of this analysis. Possibilities do exist for increasing available timber volumes; for example, harvesting in higher elevation inoperable areas, employing silvicultural techniques to shorten the time needed for trees to reach merchantable size, or improving utilization. However, in general, these possibilities are not currently practiced. Data uncertainties highlight that retaining current harvest levels in Kalum North may increase the risks that a reasonable rate of decline to a harvest level sustainable in the long run cannot be maintained, and that existing available old age timber may be harvested before second-growth timber is available.
Perhaps the most notable result of the analysis is that the current harvest is well above a level sustainable in the long run. The rates of decline in harvests shown in this analysis are about 10% per decade. If this rate is deemed too rapid, the analysis would indicate an immediate harvest reduction. Conversely, if a more rapid decline is acceptable, the analysis would indicate the potential to maintain the current harvest level for longer, assuming the data used to describe the current management regime and timber inventory are accurate.
It should also be recalled that the harvest
flows shown in this analysis represent maximum levels given current
management practices and data. Basing current management decisions,
such as harvest level, on the estimates of timber availability
shown here may reduce the flexibility of future forest managers
to meet their objectives if conditions are less favourable than
assumed.