Linking ecologically based productivity information to timber supply analysis units using site series sampling

Abstract

Timber supply analyses are used to estimate the possible harvest level of timber volume over the long term. Site index is one of the inputs of these analyses. When site index is underestimated, as is often the case for older stands, it will lead to underestimated yields. This creates a significant negative effect on harvest levels in the timber supply analyses. Better site index information is obtainable by using ecologically based site indices; however, an efficient way of applying the site index estimates is needed. The purpose of this project was to develop a technique for incorporating better site index estimates into timber supply analyses. We used simple random sampling to determine the proportion of each site series in a management unit. Site index estimates were available for these site series. To link the site index information to timber supply analysis units, we initially created analysis units using inventory information. The site series proportions were then used to form new ecologically based analysis units, and yield tables were generated from the associated site index information. After an area was harvested in the timber supply model from an inventory-based analysis unit, it was allocated to an ecologically based analysis unit in proportion to the area that the site series occupied in the timber harvesting land base. Once an area was placed into a new analysis unit, it remained there for the duration of the timber supply analysis. We tested this method in the Bulkley Timber Supply Area, where it resulted in a 26% increase in the long-term sustainable harvest level.