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Juvenile height models for lodgepole pine and interior spruce: validation of existing models and development of new models

Author(s) or contact(s): G.D. Nigh
Source: Research Branch
Subject: Growth and Yield
Series: Research Report
Other details:  Published 2004. Hardcopy is available.


Juvenile height models are available for lodgepole pine (Pinus contorta var. latifolia Dougl. ex Loud.) and interior spruce (Picea glauca (Moench) Voss, P. engelmanni Parry ex Engelmann, and P. glauca x engelmanni). These models were developed with data collected from a small area of British Columbia but are widely used because they are the best available information. The purpose of this project is to validate these models with data from six biogeoclimatic zones where lodgepole pine and interior spruce commonly occur. The target sample size of 10 plots per species per zone could not be met for one of the targeted zones, so another zone was added to the sample plan. One site tree per species in each plot was selected for sampling. The tree was felled and split lengthwise to reveal the pith nodes. Annual height was measured directly from the pith nodes. A rigorous validation procedure was used to validate the models for the province as a whole and on a zone-by-zone basis. The models showed evidence of a slight bias and therefore new models were re-fit to the new data. The functional form of the new model was modified to: 1) prevent predicted heights from being negative for low site indices; 2) improve the fit by allowing the exponent parameter to be a function of site index; and 3) allow all parameters to take on zone-specific values. Most of the difference in height growth across the zones, for a given level of site index, occurred below breast height. Early height growth was greater in the more productive zones. For situations where the models are applied in a zone that was not sampled or where the zone is unknown, the estimated heights are based on averages across all sampled zones. A small validation of the new model for lodgepole pine shows that it is adequate for estimating juvenile heights in the Interior Douglas-fir zone.

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Updated October 24, 2008