- site productivity estimates
Site indexes, determined from the ages and heights of trees, are used to estimate the productivity (growth potential) of tree-growing sites. The site indexes used in the timber supply analysis base case were accepted by Research Branch staff. However, after comparison of site indexes for cedar with those for other species, Research Branch staff concluded that the site indexes used in the base case for cedar stands, which occupy approximately 10 percent of the timber harvesting land base, are conservative. Staff believed that increasing the site indexes by 6 metres would more likely represent actual site productivity than site indexes used in the base case for areas currently occupied by cedar stands 40 years and younger, and older than 140 years, once they have been harvested and reforested. A sensitivity analysis was conducted to assess the implications of this change. The site index adjustment was not applied to cedar stands between the ages of 41 and 140 years in the sensitivity analysis because more accurate site index estimates are generally obtained for stands of these ages. The sensitivity analysis shows that if cedar site indexes have been underestimated by 6 metres, timber supply is increased slightly in the medium and long term. While the exact magnitude of the site index underestimate is uncertain, I accept, based on assessment by Research Branch staff, that young and old cedar stand site indexes are higher than assumed in the base case. This adjustment places an unquantified upward pressure on timber supply over the medium and long terms.
Further sensitivity analysis examined the timber supply impacts of applying the same 6-metre site index increase to cedar stands as discussed above (that is, only to stands younger than 41 and older than 140 years), and increasing the site index of all other species (excluding stands between the ages of 41 and 140 years) by 3 metres. This sensitivity analysis indicates substantial increases in timber supply over the medium and long terms. Research Branch staff have concurred that site indexes for species other than cedar have most likely been underestimated. However, they caution that there is significant uncertainty about the magnitude of the underestimation, since there is limited evidence specifically for TFL 45 on which to base a site index adjustment. Nevertheless, the 3-metre adjustment used in the sensitivity analysis is conservative compared to some of the preliminary results from paired plot studies in other coastal areas. I believe that site indexes for stands other than those between the ages of 41 and 140 years have likely been underestimated, but the magnitude of any underestimate, and the timber supply implications cannot be quantified at this time. I conclude that this represents an unquantified upward pressure on timber supply in the medium and long term.
A final site index sensitivity analysis examined the impact of increasing the site indexes of all cedar stands by 6 metres, and the site indexes of all stands of other species by 3 metres. In other words, it was assumed that the site indexes for stands between the ages of 41 and 140 years had also been underestimated. I do not believe it is appropriate to adjust the site indexes for these stands since there is no statistical basis for the adjustment, and since it is more likely that inventory information accurately reflects site productivity for stands in this age group.
To conclude, I accept the Research Branch assessment that young and old cedar stand site indexes are higher than assumed in the base case. Further, I am aware that evidence from other areas of the coast indicates that site indexes have been underestimated. While there is no direct evidence showing that site indexes have been underestimated in TFL 45, I accept that some underestimation is likely for the TFL. The young and old cedar stand adjustment and the likelihood of a more general underestimate of site indexes for other species exert an unquantified upward pressure on timber supply over the medium and long terms. This factor is discussed in "Reasons for Decision." A provincial paired-plot survey is expected to provide further information on site indexes for regenerating stands, which will most likely be useful for future timber supply analyses. In addition, the licensee has indicated an intent to refine site index estimates within the next 5 years. Considering the potential impacts on medium- and long-term timber supply, it is important that improved site index information be available for the next determination.
One final issue related to site productivity, as noted by BCFS staff, is that there is no site index information for approximately 1490 hectares of the timber harvesting land base. For the purposes of the timber supply analysis, this area was assumed to be characterized by medium site productivity. Research Branch considers this assumption acceptable because a large portion of sites in the TFL (65 percent) are of medium productivity, and no other information is available. I also note that most of the stands which lack site index information (1112 hectares) are young, and would have been a result of early logging which occurred mainly on the most productive sites. Therefore, I believe that the assumption used in the analysis is conservative, and until other information becomes available, I am satisfied that it is appropriate for use in this determination.
- volume estimates for regenerated stands
Estimates of volumes for existing stands less than 40 years old and future regenerated stands were projected in the timber supply analysis using the Table Interpolation Program for Stand Yields (TIPSY), which was designed for use with managed stands. Research Branch has reviewed and accepted the yield tables used to project regenerated stand volume estimates, and I am satisfied that they are appropriate for use in this determination. However, I am mindful that if site indexes have been underestimated, regenerated stand volume estimates would also be underestimated. The timber supply implications of this have been described above under site productivity estimates.
- operational adjustment factors
Operational Adjustment Factors (OAFs) are applied to regenerated stand volume estimates used in timber supply analyses in order to account for the loss of timber productivity due to particular operational conditions, such as openings in stands, pests, decay, waste and breakage. The OAFs applied in the licensee's analysis were determined based on the assumption that managed stand volumes would not exceed existing stand volumes by more than 20 to 30 percent. Research Branch has accepted the OAFs used in the analysis as reasonable. I note that these OAFs are much higher than the OAFs applied in other coastal areas, and I consider the volumes projected for managed stands to be a conservative estimate. Any potential timber supply implications would overlap with those due to site productivity changes, which I have discussed above.
- minimum harvestable ages
Minimum harvestable age is an estimate of the average time required for trees to reach a harvestable condition. In the timber supply analysis, the minimum harvestable ages were based on the ages after which further increases in the mean annual increment (MAI, i.e. the average annual volume growth) for each tree species and growing site would be less than 0.5 cubic metres per hectare each year.
Sensitivity analysis provided in the analysis shows that the timber supply is very sensitive to increases in the minimum harvestable age. If the minimum harvestable age is increased by 10 years, then the initial harvest level projected in the BCFS analysis cannot be achieved without causing significant disruptions in timber supply in the future. The initial harvest level would have to decline to 165 000 cubic metres per year (a decrease of approximately 25 percent from the initial harvest level in the base case) in order to avoid timber supply shortages in the medium term. Sensitivity analysis also shows that the harvest forecast is sensitive to decreases in minimum harvestable age. If the minimum harvestable ages are decreased by 10 years, then the initial harvest level projected in the base case can be maintained for an additional decade.
Interfor has stated that stands younger than the minimum harvestable age could be harvested if the stands meet certain merchantability criteria. If this were the case, the timber supply could be more flexible than indicated in the analysis base case. However, I do not anticipate that stands as young as the minimum harvestable age will be harvested at this time; most stands in the short and medium term are projected to be harvested at well beyond the minimum harvestable ages. Timing of availability of regenerating managed standsthat is, the minimum harvestable ageswill be important in defining timber supply, particularly in the medium term. Therefore, definition of these ages should be refined as information on the merchantability of managed stands improves. At this time, I am satisfied that the minimum harvestable ages used in the analysis are suitable for this determination.
- species profile of harvest
One of the objectives outlined in MP No. 3 for TFL 45 is to harvest timber in proportion to the existing species profile for the timber harvesting land base. This management objective was not reflected in the analysis, in which harvesting is projected to occur in the oldest stands first, regardless of species. While this approach is acceptable, and commonly used in timber supply analysis, I note that the assumptions used in the timber supply analysis do not fully reflect the harvest profile commitment made in the management plan. Although I consider it important that timber supply analyses should reflect management plan commitments, examination of the current species and age composition of the timber harvesting land base leads me to believe that the failure to explicitly model harvest of the species profile does not pose a significant risk to short-term timber supply. I have made no adjustments to my determination on this account.
(ii) the expected time that it will take the forest to become re-established on the area following denudation;