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.
Highlights
Oak is the largest tree species in China [1]
The data used to develop individual-tree diameter growth and mortality models for predicting natural Mongolian oak were collected from 195 re-measured permanent sample plots (PSP) in Wangqing Forestry Bureau, Jilin Province, Northeast China (Figure 1)
The most important explanatory variables were the log of tree diameter at breast height (DBH), stand basal area (BA), basal area larger than subject trees (BAL) and site index (SI)
Summary
Mongolian oak (Quercus mongolica Fisch.) is a main tree species of the secondary broad-leaved forest that grows mainly throughout Northeast China. It has economically important value for timber production, and has the capacity to improve environment, soil and water conservation. The selection management needs the individual tree growth and yield models because they provide good simulation of growth and mortality for short-term projections, produce detailed information about stand structure and allow consideration of a wide variety of silvicultural treatments. There are no individual tree growth models of Mongolian oak forests for good forest management with the exception of the integrated stand growth model developed by using system equations [4]
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