Abstract

In recent years optical techniques for rapid LAI measurements have been developed, but few studies have been performed to evaluate the accuracy of optical estimation of LAI in mixed deciduous-evergreen forest stands. In this paper, we assessed the accuracy of digital hemispherical photography (DHP) and the LAI-2000 for the estimation of effective LAI (L_e) by comparison with litter collection LAI (LAI_lit) in four mixed deciduous broadleaf and evergreen needleleaf forests and one deciduous needleleaf forest. We also evaluated the relative contribution of major error sources to the determination of LAI by optical methods, including the woody-to-total area ratio (α), the element clumping index (Ω_E) and the needle-to-shoot area ratio (γ_E). Additionally, incorrect automatic photographic exposure has been considered for DHP. DHP L_e underestimated LAI_lit by an average of 44-70% in different forests, and the difference between LAI_lit and DHP L_e after correction for the automatic exposure, α, Ω_E and γ_E ranged from 1% to 21% in five forest stands. In contrast, LAI values from LAI-2000 were more similar to the direct litter collection LAI. The LAI-2000 L_e underestimated LAI_lit by an average of 13-40% in these forests, while the accuracy of the best estimates of LAI using LAI-2000 methods is over 93% after considering α, Ω_E and γ_E. The error caused by automatic exposure to DHP L_e is larger than other factors in all forest stands, and the γ_E was the main uncertainty to LAI-2000 L_e in most forest stands. Moreover, optical LAI (both DHP and LAI-2000) was significantly (P < 0.01) correlated with LAI_lit, especially the corrected LAI obtained by the LAI-2000 (R² = 0.83, RMSE = 1.04). Our results demonstrate that the above factors affect the estimation of LAI by optical methods, thus the species composition of a forest stand should be seriously considered in order to improve the accuracy of LAI by optical methods.

  Keywords

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Leaf Area Index (LAI), Digital Hemispherical Photography (DHP), LAI-2000, Woody Materials, Clumping Effects, Automatic Exposure, Litter Collection, Correlation

Authors’ Info

Paper Info

Citation

Liu Z, Jin G, Zhou M (2015). Evaluation and correction of optically derived leaf area index in different temperate forests. iForest 9: 55-62. - doi: 10.3832/ifor1350-008

Academic Editor

Giorgio Matteucci

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© SISEF - The Italian Society of Silviculture and Forest Ecology 2015

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This article is distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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