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Forests 2015, 6(6), 2261-2280; doi:10.3390/f6062261

Nonlinear Simultaneous Equations for Individual-Tree Diameter Growth and Mortality Model of Natural Mongolian Oak Forests in Northeast China

1,2
and
1,*
1
Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Beijing 100091, China
2
School of Natural resources, West Virginia University, Morgantown, MD 26505, USA
*
Author to whom correspondence should be addressed.
Academic Editors: M. Altaf Arain and Eric J. Jokela
Received: 27 March 2015 / Revised: 28 May 2015 / Accepted: 12 June 2015 / Published: 23 June 2015
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Abstract

A nonlinear equation system for individual tree diameter growth and mortality of natural Mongolian oak forests was developed based on 13,360 observations from 195 permanent sample plots in Northeast China. Weighted regression was used in a distance-independent diameter growth equation for dealing with heterocedasticity. Since diameter growth and mortality models have common predictors including the diameter at breast height (DBH), stand basal area (BA), basal-area-in-larger trees (BAL), and site index (SI), parameters were estimated using nonlinear three-stage least squares (N3SLS) and seemingly unrelated regression (SUR) which accounts for correlations of errors across models. The system equation provided better projection than individual fitting of the equation based on maximum likelihood estimation. Compared with the separate tree growth model, the simultaneous equations using N3SLS and SUR produced more efficient parameter estimation and smaller bias. Furthermore, N3SLS had more accurate projection. Overall, the simultaneous model will facilitate the growth and yield projection for better management of Mongolian oak forests in the region. View Full-Text
Keywords: Individual tree diameter growth model; mortality model; weighted regression; nonlinear three-stage least squares; seemingly unrelated regression Individual tree diameter growth model; mortality model; weighted regression; nonlinear three-stage least squares; seemingly unrelated regression
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Ma, W.; Lei, X. Nonlinear Simultaneous Equations for Individual-Tree Diameter Growth and Mortality Model of Natural Mongolian Oak Forests in Northeast China. Forests 2015, 6, 2261-2280.

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