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Engelmann spruce site index models: a comparison of model functions and parameterizations
1Forest Analysis and Inventory Branch, British Columbia Ministry of Forests, Lands and Natural Resource Operations, Victoria, British Columbia, Canada.
Plos One
|April 9, 2015
Summary
Developing accurate site index models for Engelmann spruce is crucial for forest management. The indicator variable parameterization offered the best fit, though practical application barriers exist for all methods.
Area of Science:
- Forestry and Silviculture
- Quantitative Ecology
- Biometrics
Background:
- Engelmann spruce (Picea engelmannii) is a vital high-elevation timber species in western North America.
- Increased harvesting necessitates improved height growth models for effective forest management.
- Existing models lack sufficient accuracy for current management demands.
Purpose of the Study:
- To develop a site index model for Engelmann spruce growth.
- To compare model formulations (Chapman-Richards, Hossfeld IV, Schumacher) and parameterizations (indicator variables, mixed-effects, GADA, g-GADA).
- To specifically analyze the grounded-Generalized Algebraic Difference Approach (g-GADA) parameterization.
Main Methods:
- Utilized stem analysis data from 84 Engelmann spruce trees across the Engelmann Spruce - Subalpine Fir zone.
- Fitted models using Chapman-Richards, modified Hossfeld IV, and Schumacher functions.
- Evaluated models using corrected Akaike's Information Criteria and estimated variance.
Main Results:
- Model parameterization significantly impacted fit more than model formulation.
- Indicator variable parameterization yielded the best model fit.
- Mixed-effects, g-GADA, and GADA parameterizations showed increased variance (9% to 346%) compared to indicator variables.
Conclusions:
- The indicator variable parameterization provides the most accurate site index model for Engelmann spruce.
- Practical application challenges, including data and software needs, must be considered when selecting a model.
- Further research into accessible parameterization methods is warranted.
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