Forests, Lands, and NR Operations

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Revised site index models for western redcedar for coastal British Columbia

Author(s) or contact(s): G.D. Nigh
Source: Forests, Lands, and NR Operations
Subject: Growth and Yield
Series: Technical Report
Other details:  Published 2016. Hardcopy is available.


The British Columbia Ministry of Forests, Lands and Natural Resource Operations is implementing a program to update site index models by refitting the models with newer fitting techniques. The existing site index model for coastal western redcedar (Thuja plicata) was developed by MacMillan Bloedel
Limited in 1978. This model was in particular need of updating because it gave unreasonable height and site index predictions for old trees and because
some abnormalities in the height predictions were fixed with ad hoc adjustments. Data for the refit were obtained from four sources: pseudo-data from the existing model, stem analysis data from a wood quality study, a foliar nutrient-growth study, and a project done by MacMillan Bloedel. The grounded-Generalized Algebraic Difference Approach was applied to a Chapman-Richards function to derive a base-age invariant site index model for coastal western redcedar. This new site index model fit the data well and gave approximately the same height predictions as its predecessor over the range of data used to develop the forerunner model, but gave more reasonable height and site index predictions when extrapolated to older ages.

Supplement to Technical Report 105

The supplement to Technical Report 105 describes a method to estimate the unknown Parameter, presented in the site index model of Technical Report 105, from site index without nonlinear optimization software.

Download Technical Report 105 (792 KB)

Dowload Supplement to Technical Report 105 (31 KB)

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Updated June 23, 2017