After debate about the estimated reductions in Timber Harvesting Land Base (THLB) due to riparian management in the Mackenzie Timber Supply Area (TSA), the Chief Forester of British Columbia requested improved estimates of riparian areas for purposes of future Timber Supply Reviews. We used a Bayesian Belief Network (BBN) approach to model riparian management areas and used previously collected data to test and recalibrate the model. The Riparian Habitat Assessment and Supply Estimator (RHASE) operates on pre-field data available through standard sources (e.g., Terrestrial Resource Inventory Management, Forest Cover, and Ecological Mapping). RHASE performed with 70% accuracy (n = 417) in determining stream widths with most error equally split between false positives (18%) and false negatives (12%). Predicted riparian management areas resulted in exclusions exceeding 11% of the net operable forest using similar aspatial methods and riparian management reduction factors as those adopted for the last TSR but with much larger sample sizes. Using default riparian management reductions from the more current Forest Planning and Practices Regulations in the same aspatial analysis led to a 9.22% impact on the THLB, 2.05% increase over the factor used in TSR2. We conclude that the aspatial reduction estimate used in TSR2 was biased low mostly due to a low sample size. However, and more importantly, in completing this analysis, we also conclude that strong spatial bias leads to an overestimate of the impact at both coarse- and fine-textured resolutions. Most obvious was a tendency to apply riparian impacts against a relatively sparse THLB in regions that are not highly productive for timber. Using the same riparian estimates applied to the same THLB, we calculated a 5.33% impact when the estimate was derived in a spatially explicit manner. The spatial estimate between 5 and 6% was recommended for use in subsequent Tsar's given its inherent analytical and methodological strength compared to previously calculated aspatial estimates.
R. Scott McNay, Jacqueline L. Caldwell and Randy Sulyma,
Forest Investment Account (FIA). 2005. Impact of riparian management on timber supply in Mackenzie TSA, British Columbia:. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2005MR111