Lillooet, AAC Rationale

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- volume estimates for regenerated stands


The BCFS uses the Table Interpolation Program for Stand Yields (TIPSY) to estimate volumes from managed stands. Volumes projected using TIPSY assume management practices such as control of stocking density through planting, brushing and spacing. In the Lillooet timber supply analysis, only a minor portion of the existing stands under 40 years of age was assumed to meet current requirements for managed stand conditions and was ascribed a managed stand yield curve. Volume estimates for the majority of existing regenerated stands were therefore estimated using VDYP. It was assumed that all not-satisfactorily-restocked (NSR) areas and all stands harvested in the future will be managed such that they will grow according to TIPSY predictions. Volumes in stands managed by selection harvesting were also estimated using their VDYP curve.

For managed stands where TIPSY was used, Operational Adjustment Factors (OAFs) were applied to account for a loss of timber volume due to such factors as openings in stands (OAF1), as well as age-dependent factors such as pests, disease, decay, waste and breakage (OAF2). The Lillooet timber supply analysis used the provincial standard OAFs of 15 and 5 percent respectively. There is concern about the presence of root disease and other stand-damaging agents within the TSA. Root disease is most prevalent in Douglas-fir stands managed primarily by selection harvesting. Research into root disease and its impacts on timber supply is proceeding in various parts of the province, and I expect future analyses will have the benefit of improved information regarding appropriate OAFs. However, at this time, the OAFs assumed in the base case reflect the best available information and I accept them as appropriate for use in this determination.

The CLMA raised a concern that VDYP curves may be inappropriate for stands managed by selection harvesting. I agree that an uneven-aged stand model is needed, and the BCFS is currently developing such a model for future use. However, I am aware of no information that would allow me to determine if any future model would increase or decrease estimated volumes from selection stands relative to the base case. At present, the method used represents the best available information. I therefore consider the current method appropriate for this determination.

District staff have assessed stocking levels in recently planted stands within the TSA and found them to be below those assumed in TIPSY. District staff found average initial stocking levels to be 893 stems/ha versus the 1120 stems/ha average assumed for the BCFS analysis using TIPSY. District staff attributed this difference to the fact that areas are sometimes planted at minimum stocking levels and the anticipated fill-in by natural regeneration is not occurring to the extent expected. If these lower stocking levels continue, regenerated volumes may be lower than predicted, which would affect the long term timber supply level. However, sensitivity analysis shows that there is no effect on the short-term timber supply in this TSA when regenerated stand volumes are either 20 percent higher or lower than assumed in the base case. Therefore, I am satisfied that base case assumptions for stocking and volume estimates for regenerated stands are satisfactory for the purposes of this determination.

Nevertheless, I am concerned about the medium- and long-term timber supply implications of the low stocking levels observed in the TSA. District staff therefore will be examining this matter further and will monitor performance to ensure compliance with target stocking levels. Furthermore, I will be following up on this matter in preparation for the next review of this AAC to ensure satisfactory compliance with provincial standards and objectives in this regard.

From the foregoing, for the purposes of this determination, I am satisfied that regenerated volumes have been adequately represented in the BCFS analysis, and that no adjustment to the projected short-term harvest level is required on this account.

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