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Optimization of leaf area index measurement method and correction of green plot ratio formula based on regional plant characteristics—a study in Chongqing, China

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Abstract

The quantification of green space green plot ratio (GPR) is mostly based on estimation formulas, and the leaf area index (LAI) estimation values in these estimation formulas have not been well verified by measured LAI values, resulting in errors and uncertainties in GPR quantification results. This study aims to address this gap by measuring the LAI of 113 regional plants in Chongqing, China, following a standardized measurement path for digital hemispherical photography (DHP). The results indicate that the optimal relative exposure value (REV) was − 1 under overcast conditions and − 2 under sunny and cloudy conditions. Among the threshold algorithms for hemispherical images, the Intermodes algorithm in ImageJ was the best. The LAI of regional plants is highest in summer, followed by spring and autumn, and lowest in winter. Tree height (h) and crown width (w) are key factors affecting LAI, but the LAI also varies with plant species. Overall, the LAI of evergreen trees is higher than that of deciduous trees. The LAI of evergreen trees and shrubs with a height shorter than 5 m is the largest, and that of deciduous trees and shrubs with a crown width larger than 8 m is the largest. The study further verified that the existing GPR estimation formula exhibited large errors in Chongqing, while there was a strong correlation (R2 = 0.973) between the GPR estimation value and the measured value. A conversion formula was developed to reduce estimation biases, and the corrected formula is capable of estimating GPR values more accurately when actual LAI measurements are insufficient. Overall, this study verifies the significance of measuring localized LAI values, promotes the understanding of LAI suitability for GPR calculations, and provides an empirical formula for GPR estimation in Chongqing, China.

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Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

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Acknowledgements

Many thanks go to the Master’s students at the College of Architecture and Urban Planning at Chongqing Jiaotong University for photography.

Funding

This project was financially supported by the Chongqing Urban Management Scientific Research Project “Optimization of Green Space Plant Allocation Pattern in Residential Areas of Chongqing’s Main City Based on Green Capacity Rate Measurement” with No. (32) in the Urban Management Section 2022.This project was also funded by the Chongqing Talents Program project “Study on the healing mechanism of urban and rural green areas in Sichuan and Chongqing in post-epipathic period”, project number: cstc2021ycjh-bgzxm0030.

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Authors and Affiliations

  1. College of Architecture and Urban Planning, Chongqing Jiaotong University, Chongqing, 400074, China

    Lili Dong & Yawei Jiang

  2. Department of Architecture, The University of Kitakyushu, 1-1 Hibikino, Wakamatsu, Kitakyushu City, Fukuoka, 808-0135, Japan

    Yu Luo

  3. Centre for Climate-Resilient and Low-Carbon Cities, School of Architecture and Urban Planning, Chongqing University, Chongqing, 400045, China

    Xiang Cheng

  4. Chongqing Key Laboratory of Germplasm Innovation and Utilization of Native Plants, Chongqing, 401329, China

    Lijiao Ai

  5. Chongqing Landscape and Gardening Research Institute, Chongqing, 401329, China

    Lijiao Ai

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  1. Lili Dong
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  2. Yawei Jiang
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  3. Yu Luo
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  4. Xiang Cheng
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Contributions

Lili Dong: conceptualization, data curation, formal analysis, investigation, methodology, validation, visualization, software, writing of the original draft. Yawei Jiang: data curation, investigation, validation, software, writing, review, and editing. Yu Luo: investigation, methodology, validation, visualization, writing—review, and editing. Xiang Cheng: data curation, investigation, validation, writing, reviewing, and editing. Lijiao Ai: conceptualization, data curation, formal analysis, funding acquisition, visualization, software investigation, writing, review, and editing.

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Correspondence to Lili Dong.

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Appendix

Appendix

Tables 12, 13, and 14

Table 12 LAI index table of common local plants in Chongqing in spring and summer
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Table 13 LAI indices of common local plants in Chongqing in autumn and winter
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Table 14 LAI estimation table for commonly used summer regional plants in Chongqing
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Dong, L., Jiang, Y., Luo, Y. et al. Optimization of leaf area index measurement method and correction of green plot ratio formula based on regional plant characteristics—a study in Chongqing, China. Environ Sci Pollut Res (2024). https://doi.org/10.1007/s11356-024-33125-z

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