Development of Growth Intercept Models
Sunpine Forest Products Ltd.
Lead Researcher: 
Bob Held, Sunpine Forest Products Ltd., Sundre, Alberta
Site index equations are highly relative to mature stands, however the equations or site curves are less accurate in estimating the site index of young stands. The height growth of younger trees tends to be more sporadic and therefore greater variation exists in site index curves at younger ages. The use of growth intercept models allows for more accurate estimates of site index at younger ages. The goal of this project was to provide Sunpine Forest Products with the appropriate operational growth intercept (GI) models for lodgepole pine as well as a draft strategy for applying GI models to the landbase.

The project began with the destructive sampling of 108 lodgepole pine site-trees in 37 plots located across a range of poor, medium and good sites in the Sunpine Forest Management Agreement (FMA) area.

Fixed-time growth intercept models, relate site index to a specified time interval above a reference height. The growth intercept is the annual height growth for the first 3, 4, 5 and 6 years above the reference height (i.e. 0.3, 0.75 and 1.3 m). In contrast to fixed-time modeling, variable-time growth intercept models allow the user to input variable heights thus adding to the flexibility of application in the field. This procedure relates total length above the reference height (RH) and the time interval in years above that RH. Both models can be used in the field provided the age input is accurate.