In recent years, forest managers have become increasingly aware of biased estimates of site index that are common in the forest inventory. The biases arise primarily from estimates of site index from old stands, which are prevalent in the inventory in many areas of the province. Specific causes include uncertainty in the height/age curves for old stands, height/age pairs from trees/ stands that underwent significant periods of suppression (i.e. in multi-aged stands) and lodgepole pine repression, all of which lead to underestimates of site index. These biases have important implications for timber supply analysis and strategic silviculture planning, as relatively small increments of site index have significant effects on predicted forest yields. Acquiring accurate estimates of site index have thus become an important focus in many timber supply areas. Several methods of correcting site index estimates have been employed. Earlier examples included paired plot and veteran studies, where estimates of SI that were known to be biased were compared to immediately adjacent sources of estimates that are believed to be more reliable. Results from these studies have been used in some analyses to make coarse, broad scale adjustments to SI estimates, although often simply to test sensitivity to possible bias. More recently, methods have evolved to extensively sample certain management units, with the intent of developing statistically defensible, locally applicable adjustments. This document outlines the methodology to be applied for such a project in Timber Supply Area (TSA) portions of the Prince George and Fort St. James Forest Districts. It follows closely the strategy used in 2003/04 for the Vanderhoof District, which together with Prince George and Fort St. James (Figure 1) make up the Prince George Timber Supply Area (TSA). The common methodology employed will help make the application of the adjustments as simple as possible in any future TSA analyses.
Farnden, Craig. 2005. Site Index Adjustment for the Prince George and Fort St. James Forest Districts: Sample Plan. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2005MR023
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA)
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