Growth intercept models estimate site index (a measure of site productivity) from average tree height growth measured immediately above breast height. These models have been developed for four species: coastal western hemlock (Tsuga heterophylla (Raf.) Sarg.) (Nigh 1996a) and Sitka spruce (Picea sitchensis (Bong.) Carr.) (Nigh 1996b); interior lodgepole pine (Pinus contorta Dougl.) (Nigh 1995a) and spruce (P. glauca (Moench) Voss, P. engelmannii Parry, and P. glauca x engelmannii) (Nigh 1995b). Growth intercept models are expected to be developed for all commercial species in British Columbia.
It is important that these models be validated (tested). Growth intercept models are empirical; hence they strongly reflect the behaviour of the model development data. Therefore, testing them with independent data (that is, data that were not used to develop the model) is important because the model development data may be atypical (Picard and Cook 1984). If a model validates well against an independent data set, it does not mean that it is correct; it simply provides more evidence that the model is adequate (Oreskes et al. 1994).
This Extension Note describes the interim validation of the coastal western hemlock growth intercept model
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Updated April 13, 2007