A new method of calculating crown projection area and its comparative accuracy with conventional calculations for asymmetric tree crowns  

作　　者：Mingrui Zhang Huiquan Bi Xingji Jin Michael McLean 

机构地区：[1]School of Forestry,Northeast Forestry University,Harbin 150040,People’s Republic of China [2]Forest Science,NSW Department of Primary Industries,Level 30,4PSQ,12 Darcy Street,Parramatta,NSW 2150,Australia [3]School of Ecosystem and Forest Sciences,The University of Melbourne,Melbourne 3010,Australia

出　　处：《Journal of Forestry Research》2024年第4期171-188,共18页林业研究（英文版）

基　　金：supported by the Natural Science Foundation of China (32071758);the Fundamental Research Funds for the Central Universities of China (No. 2572020BA01)

摘　　要：This paper introduces a new method of calculating crown projection area(CPA),the area of level ground covered by a vertical projection of a tree crown from measured crown radii through numerical interpolation and integration.This novel method and other four existing methods of calculating CPA were compared using detailed crown radius measurements from 30 tall trees of Eucalyptus pilularis variable in crown size,shape,and asymmetry.The four existing methods included the polygonal approach and three ways of calculating CPA as the area of a circle using the arithmetic,geometric and quadratic mean radius.Comparisons were made across a sequence of eight non-consecutive numbers(from 2 to 16)of measured crown radii for each tree over the range of crown asymmetry of the 30 trees through generalized linear models and multiple comparisons of means.The sequence covered the range of the number of crown radii measured for calculating the CPA of a tree in the literature.A crown asymmetry index within the unit interval was calculated for each tree to serve as a normative measure.With a slight overestimation of 2.2%on average and an overall mean error size of 7.9%across the numbers of crown radii that were compared,our new method was the least biased and most accurate.Calculating CPA as a circle using the quadratic mean crown radius was the second best,which had an average overestimation of 4.5%and overall mean error size of 8.8%.These two methods remained by and large unbiased as crown asymmetry increased,while the other three methods showed larger bias of underestimation.For the conventional method of using the arithmetic mean crown radius to calculate CPA as a circle,bias correction factors were developed as a function of crown asymmetry index to delineate the increasing magnitude of bias associated with greater degrees of crown asymmetry.This study reveals and demonstrates such relationships between the accuracy of CPA calculations and crown asymmetry and will help increase awareness among researchers and practitioners on th

关 键 词：Crown radius measurements Interpolated crown contour Projected crown area Multiple comparisons of means 

分 类 号：S758[农业科学—森林经理学]