The growth intercept method predicts site index from height and age measurements taken on carefully selected sample trees. This method of calculating site index is being calibrated for many tree species in B.C. As of August 1995, the method was available for interior lodgepole pine, interior spruce, and coastal western hemlock. In 1996, growth intercept tables will be available for coastal Douglas-fir, interior Douglas-fir, and interior western hemlock.
These procedures replace those described in the memo Using the preliminary growth intercept method to estimate site index in young
The old preliminary method required the surveyor to identify the first five annual branch whorls immediately above breast height and measure this amount of height growth. The new method, described in this document, requires the surveyor to measure total tree height and age at breast height.
Compared to the old method, the new method has the following benefits:
- Can be applied to younger stands;
- Is suitable for species with and without regular annual branch whorls;
- Produces a more accurate site index estimate under many circumstances; and
- Integrates better with existing and proposed silviculture survey methods.
* Memo dated October 14, 1994, from Henry Benskin, Director, Silviculture Branch, to all regional silviculture officers and district silviculture resource officers.
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Updated November 21, 2008