Modelling the Tree Height, Crown Base Height, and Effective Crown Height of Pinus koraiensis Plantations Based on Knot Analysis

Wancai Zhu,Dandan Li,Zhaogang Liu,Weiwei Jia

doi:10.3390/f12121778

Wancai Zhu, Dandan Li + Show 2 more

Open Access

https://doi.org/10.3390/f12121778

Copy DOI

Abstract

Taking 1735 Pinus koraiensis knots in Mengjiagang Forest Farm plantations in Jiamusi City, Heilongjiang Province as the research object, a dynamic tree height, effective crown height, and crown base height growth model was developed using 349 screened knots. The Richards equation was selected as the basic model to develop a crown base height and effective crown height nonlinear mixed-effects model considering random tree-level effects. Model parameters were estimated with the non-liner mixed effect model (NLMIXED) Statistical Analysis System (SAS) module. The akaike information criterion (AIC), bayesian information criterion (BIC), −2 Log likelihood (−2LL), adjusted coefficient (Ra2), root mean square error (RMSE), and residual squared sum (RSS) values were used for the optimal model selection and performance evaluation. When tested with independent sample data, the mixed-effects model tree effects-considering outperformed the traditional model regarding their goodness of fit and validation; the two-parameter mixed-effects model outperformed the one-parameter model. Pinus koraiensis pruning times and intensities were calculated using the developed model. The difference between the effective crown and crown base heights was 1.01 m at the 15th year; thus, artificial pruning could occur. Initial pruning was performed with a 1.01 m intensity in the 15th year. Five pruning were required throughout the young forest period; the average pruning intensity was 1.46 m. The pruning interval did not differ extensively in the half-mature forest period, while the intensity decreased significantly. The final pruning intensity was only 0.34 m.

Highlights

The crown size of a tree reflects its photosynthetic ability and contains ecological legacy information related to the past history of the individual tree; the crown size can provide a reference for present and future tree growth [1,2,3,4]
The dynamic variations in the height to crown base and height to effective crown can be remeasured within equal intervals, these measurements are relatively difficult and time consuming to obtain, and the information provided by these measurements is still limited [12]
The data used in the present study were collected from 12 planted Korean pine sample plots that were developed in different forest stands in the Mengjiagang Forest Farm in 2010; each plot had an area of 0.06 hm2

Summary

Introduction

The crown size of a tree reflects its photosynthetic ability and contains ecological legacy information related to the past history of the individual tree; the crown size can provide a reference for present and future tree growth [1,2,3,4]. The tree crown can be classified into the “effective crown” and “non-effective crown” in the vertical direction based on whether the branches can contribute excess photosynthetic products for trunk growth [9,10]. Quantifying the height to the effective crown can provide reasonable pruning guidance and improve the timber quality of trees [11]. The knots in a stem can yield abundant information related to crown structure dynamics throughout the lifetime of a tree, and the height to the crown base and height to the effective crown can be accurately quantified using stem knots [13]. In the present study, we mainly focused on modelling tree height, height to the crown base, and heights to effective crown using the knot-analysis approach

Objectives

Methods

Results