Chinese Bulletin of Botany ›› 2018, Vol. 53 ›› Issue (5): 671-685.DOI: 10.11983/CBB17083

• TECHNIQUES AND METHODS • Previous Articles     Next Articles

A Modification of the Finite-length Averaging Method in Measuring Leaf Area Index in Field

Liu Qiang1,2,*(), Cai Erli1, Zhang Jialin1, Song Qiao1, Li Xiuhong1,2, Dou Baocheng1,2   

  1. 1College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China
    2State Key Laboratory of Remote Sensing Science, Jointly Sponsored by Beijing Normal University and Institute of Remote Sensing and Digital Earth, Chinese Academy and Sciences, Beijing 100875, China
  • Received:2017-04-14 Accepted:2017-08-30 Online:2018-09-01 Published:2018-11-29
  • Contact: Liu Qiang
  • About author:

    † These authors contributed equally to this paper

Abstract:

Measuring leaf area index (LAI) in the field is a common task in ecological and agricultural studies. There are direct and indirect methods for the task. One of the frequently used indirect methods is to acquire a digital photo of the vegetation canopy and extract the area ratio of green leaf, then simultaneously estimate LAI and clumping index with the finite-length averaging method proposed by Lang and Xiang (1986). However, the finite-length averaging method still needs improvement. For example, using Beer’s law for estimating leaf area in the sample’s line of finite length is theoretically incompatible with its basic assumption of heterogeneous canopy, resulting in over-estimation or even invalid value of the calculated LAI. Thus, this study proposed empirical formulas to replace Beer’s law in characterizing the relation between gap ration and LAI in the sample line (or sample square) based on computer simulations. The new formulas correct the shortcomings of over-estimation and instability of Beer’s law when the canopy is dense and the length of sample line (or sample square) is short. Then, the optimal setting for the length of sample line (or sample square) in a heterogeneous field is discussed: the length of 8 times an equivalent leaf length for sample line and 3 times an equivalent leaf length for a sample square were recommended in most cases of crop or grass scenes. As well, a sample square was superior to a sample line in applications estimating LAI of a heterogeneous field.

Key words: leaf area index, clumping index, Beer’s law;, sampling method