Describing leaf area distribution in loblolly pine trees with Johnson's SB function

Abstract

The objective of this study is to evaluate the fit of Johnson's S B distribution function to vertical foliage distributions of variously aged and treated loblolly pine trees when the function is fit with two percentiles of the observed distributions. Foliage distributions are linked to various stand properties, and straightforward means of quantifying foliage distribution may lead to a convenient method of characterizing forest stands using remote sensing technology such as LiDAR. Regression analyses indicate that the 15th and 50th percentiles of the distributions were best correlated with variables of crown structure and tree age. Skewness and kurtosis of the distributions calculated with the function's parameters also varied with crown structure and age. Cumulative fractions of leaf area calculated with fitted SB functions matched measured values well; cumulative values of absolute leaf area showed less correspondence with measured values, but residuals of both centered around zero. Incompatibilities between the continuous SB function and the irregular and discrete nature of foliage distribution of single trees occasionally produced large prediction errors. Based on these results, the SB function fitted with the two-percentile method suitably describes the vertical distribution of leaf area of a wide variety of loblolly pine trees. Copyright © 2005 by the Society of American Foresters.