Chin J Plan Ecolo ›› 2016, Vol. 40 ›› Issue (6): 574-584.DOI: 10.17521/cjpe.2015.0467

• Research Articles • Previous Articles     Next Articles

Improving the accuracy of indirect methods in estimating leaf area index using three correction schemes in a Larix gmelinii plantation

Ming ZHOU1,2, Zhi-Li LIU1, Guang-Ze JIN1,*()   

  1. 1Center for Ecological Research, Northeast Forestry University, Harbin 150040, China
    and
    2Forestry Bureau of Jiamusi, Jiamusi, Heilongjiang 154007, China
  • Received:2015-12-21 Accepted:2016-05-09 Online:2016-06-30 Published:2016-06-15
  • Contact: Guang-Ze JIN

Abstract:

Aims Woody materials and clumping effects are key error sources in estimating leaf area index (LAI) by optical methods. However, how to correct the error caused by woody materials has not reached consensus. The aims of this study are (1) to evaluate the accuracy of optical methods for estimating effective LAI (Le) in a deciduous needle leaf forest stand, and (2) to develop a practical correction scheme to improve the accuracy of optical methods in estimating LAI.Methods Lewas estimated by two indirect methods (i.e., digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer method (LAI-2000 method) in an annual maximum leaf area period in a Larix gmelinii plantation. Then, we developed three correction schemes to improve the accuracy of indirect methods in estimating LAI. Meanwhile, two direct methods (i.e., litter collection and allometry methods) were used to estimate LAI. Taking LAI from litter collection as a reference, we evaluated the effectiveness of three correction schemes and tested the influence of zenith angle ranges on the correction results.Important findings With zenith angle ranges of 0-45° (rings 1-3), 0-60° (rings 1-4), 45°-60° (ring 4) and 0-75° (rings 1-5), Leobtained from DHP underestimated LAI from both litter collection and allometry by 19%-32% and 18%-29%, respectively. Lefrom LAI-2000 method with four zenith angles also underestimated LAI from both litter collection and allometry by 9%-30% and 8%-28%, respectively. Although the contribution of woody materials to LAI was overestimated in correction scheme A, it was effective in correcting Lefrom DHP with zenith angles of 45º-60º (ring 4), and also effective for Lefrom LAI-2000 method with zenith angles of rings both 1-3 and 1-4. Correction scheme B was all effective in correcting Lefrom DHP with four zenith angle ranges. Generally, correction scheme C was more effective than other two schemes in correcting Lefrom both DHP and LAI-2000 method with four zenith angle ranges. These results indicate that the zenith angle range is a key factor for determining the accuracy of optical methods in estimating LAI besides woody materials and clumping effects.

Key words: leaf area index, litter collection, allometry, digital hemispherical photography, LAI-2000 plant canopy analyzer method, zenith angle