Estimating Needle and Shoot Inclination Angle Distributions and Projection Functions in Five Larix principis-rupprechtii Plots via Leveled Digital Camera Photography

Jie Zou,Peihong Zhong,Wei Hou,Peng Leng,Yong Zuo

doi:10.3390/f12010030

Jie Zou, Peihong Zhong + Show 3 more

Open Access

https://doi.org/10.3390/f12010030

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Abstract

The leaf inclination angle distribution function is a key determinant that influences radiation penetration through forest canopies. In this study, the needle and shoot inclination angle distributions of five contrasting Larix principis-rupprechtii plots were obtained via the frequently used leveled digital camera photography method. We also developed a quasi-automatic method to derive the needle inclination angles based on photographs obtained using the leveled digital camera photography method and further verified using manual measurements. Then, the variations of shoot and needle inclination angle distributions due to height levels, plots, and observation years were investigated. The results showed that the developed quasi-automatic method is effective in deriving needle inclination angles. The shoot and needle inclination angle distributions at the whole-canopy scale tended to be planophile and exhibited minor variations with plots and observation years. The small variations in the needle inclination angle distributions with height level in the five plots might be caused by contrasting light conditions at different height levels. The whole-canopy and height level needle projection functions also tended to be planophile, and minor needle projection function variations with plots and observation years were observed. We attempted to derive the shoot projection functions of the five plots by using a simple and applicable method and further evaluated the performance of the new method.

Highlights

The leaf inclination angle distribution function (LIDF), which is defined as the probability of a leaf element of unit size to have its surface normal within a specified unit solid angle [1,2], is a key determinant influencing radiation penetration through forest canopies [3]
The LIDF is the fundamental parameter used to derive the leaf projection function, which is defined as the projection coefficient of the unit foliage area on a plane perpendicular to the viewing direction [2]
Some direct methods have been successfully applied to measure the LIDFs of low-vegetation canopies by using combinations of inclinometers, compasses and rulers [2,4], mechanical arms [5], and 3D digitizers [6,7], they are difficult to apply in tall canopies, such as forest canopies, because they must be in contact with leaves, which are usually distant from the ground instrument and operator

Summary

Introduction

The leaf inclination angle distribution function (LIDF), which is defined as the probability of a leaf element of unit size to have its surface normal within a specified unit solid angle [1,2], is a key determinant influencing radiation penetration through forest canopies [3]. The LIDF is the fundamental parameter used to derive the leaf projection function (commonly referred to as G), which is defined as the projection coefficient of the unit foliage area on a plane perpendicular to the viewing direction [2]. This coefficient is required as the key parameter for the indirect estimation of the leaf area index (LAI) using optical methods. For DHP, one of the two solutions is to obtain the LIDFs by inverting the simultaneous equations representing the gap fraction measurements at multiple zenith angles based on the least squares method [8,10,25]. Accurate LIDF measurements of broadleaf forest plots have been obtained using terrestrial laser scanning (TLS) [18,19,20,21,22,23,24]

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