Comparison of Different Height–Diameter Modelling Techniques for Prediction of Site Productivity in Natural Uneven-Aged Pure Stands

Guangshuang Duan,Liyong Fu,Qiuyan Wang,Zhigang Gao

doi:10.3390/f9020063

Abstract

Reliable estimates of forest site productivity are a central element of forest management. The model of height-diameter relationship of dominant trees using algebraic difference approach (ADA) is a commonly used method to measure site productivity of natural uneven-aged stands. However, the existing models of this method do not recognize site type or sample plot specific variability in height curves; thus, it cannot be effectively used to estimate site type or sample plot-related site productivity for natural uneven-aged stands. Two primary subject-specific approaches, ADA with dummy variable (DV) (ADA + DV) and ADA with combination of dummy variable and nonlinear mixed-effects modelling (CM) (ADA + CM), were proposed for height–diameter modelling. Height–diameter models developed with ADA, ADA + DV and ADA + CM were compared using data from 4161 observations on 349 permanent sample plots of four major natural uneven-aged pure stands (Spruce, Korean Larch, Mongolian Oak, and White Birch) in northeastern China. It was found that models developed with ADA + CM provided the best performance, followed by the models with ADA + DV, and the models developed with ADA performed the worst. Random effects at the plot level were substantial, and their inclusion greatly improved the model’s accuracy. More importantly, the models developed with ADA + CM provide an effective method for quantifying site type- and sample plot-specific forest site productivity for uneven-aged pure stands.

Highlights

IntroductionEstimates of forest site productivity are a central element of forest management and planning [1]
Estimates of forest site productivity are a central element of forest management and planning [1].These estimates provide critical information to forecast rates of change and to evaluate potential production of wood or biomass under different management prescriptions
Similar to the conclusion obtained by Huang and Titus [7], the use of site productivity index (SPI) as determined by the dominant and codominant H–D relationship is by no means the final solution, it provides a simple and reasonable index of site productivity for the four main natural uneven-aged pure stands of Spruce, Korean Larch, Mongolian Oak, and White Birch in northeastern China (Figure 4)

Summary

Introduction

Estimates of forest site productivity are a central element of forest management and planning [1]. These estimates provide critical information to forecast rates of change and to evaluate potential production of wood or biomass under different management prescriptions. One of the most widely used indicators of site productivity is site index (SI), which is defined as the average height of dominant (or dominant and codominant) trees at a specific reference age [2,3,4]. Developing height–age equations based on data obtained from dominant trees to determine SI is a relatively simple, proven, and effective method for assessing site productivity [9]

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Conclusion