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Estimating the volume growth of forest ecosystems accurately is important for understanding carbon sequestration and achieving carbon neutrality goals. However, the key environmental factors affecting volume growth differ across various scales and plant functional types. This study was, therefore, conducted to estimate the volume growth of Larix and Quercus forests based on national-scale forestry inventory data in China and its influencing factors using random forest algorithms. The results showed that the model performances of volume growth in natural forests (R2 ​= ​0.65 for Larix and 0.66 for Quercus, respectively) were better than those in planted forests (R2 ​= ​0.44 for Larix and 0.40 for Quercus, respectively). In both natural and planted forests, the stand age showed a strong relative importance for volume growth (8.6%–66.2%), while the edaphic and climatic variables had a limited relative importance (< 6.0%). The relationship between stand age and volume growth was unimodal in natural forests and linear increase in planted Quercus forests. And the specific locations (i.e., altitude and aspect) of sampling plots exhibited high relative importance for volume growth in planted forests (4.1%–18.2%). Altitude positively affected volume growth in planted Larix forests but controlled volume growth negatively in planted Quercus forests. Similarly, the effects of other environmental factors on volume growth also differed in both stand origins (planted versus natural) and plant functional types (Larix versus Quercus). These results highlighted that the stand age was the most important predictor for volume growth and there were diverse effects of environmental factors on volume growth among stand origins and plant functional types. Our findings will provide a good framework for site-specific recommendations regarding the management practices necessary to maintain the volume growth in China's forest ecosystems.


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Using machine learning algorithms to estimate stand volume growth of Larix and Quercus forests based on national-scale Forest Inventory data in China

Show Author's information Huiling TianaJianhua Zhua,b,*( )Xiao HecXinyun ChendZunji JianaChenyu LiaQiangxin OueQi LiaGuosheng HuangdChangfu Liua,bWenfa Xiaoa,b,**( )
Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Key Laboratory of Forest Ecology and Environment of National Forestry and Grassland Administration, Beijing, 100091, China
Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing, 210037, China
Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Key Laboratory of Forest Management and Growth Modeling, National Forestry and Grassland Administration, Beijing, 100091, China
Academy of Forest Inventory and Planning, National Forestry and Grassland Administration, Beijing, 100714, China
School of Forestry and Landscape Architecture, Anhui Agricultural University, Hefei, 230036, Anhui, China

* Corresponding author. Institute of Forest Ecology, Environment and Nature Conservation, Chinese Academy of Forestry, No. 1 of Dongxiaofu, Xiangshan Road, Haidian District, Beijing, 100091, China.

** Corresponding author. Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Key Laboratory of Forest Ecology and Environment of National Forestry and Grassland Administration, Beijing, 100091, China.

Abstract

Estimating the volume growth of forest ecosystems accurately is important for understanding carbon sequestration and achieving carbon neutrality goals. However, the key environmental factors affecting volume growth differ across various scales and plant functional types. This study was, therefore, conducted to estimate the volume growth of Larix and Quercus forests based on national-scale forestry inventory data in China and its influencing factors using random forest algorithms. The results showed that the model performances of volume growth in natural forests (R2 ​= ​0.65 for Larix and 0.66 for Quercus, respectively) were better than those in planted forests (R2 ​= ​0.44 for Larix and 0.40 for Quercus, respectively). In both natural and planted forests, the stand age showed a strong relative importance for volume growth (8.6%–66.2%), while the edaphic and climatic variables had a limited relative importance (< 6.0%). The relationship between stand age and volume growth was unimodal in natural forests and linear increase in planted Quercus forests. And the specific locations (i.e., altitude and aspect) of sampling plots exhibited high relative importance for volume growth in planted forests (4.1%–18.2%). Altitude positively affected volume growth in planted Larix forests but controlled volume growth negatively in planted Quercus forests. Similarly, the effects of other environmental factors on volume growth also differed in both stand origins (planted versus natural) and plant functional types (Larix versus Quercus). These results highlighted that the stand age was the most important predictor for volume growth and there were diverse effects of environmental factors on volume growth among stand origins and plant functional types. Our findings will provide a good framework for site-specific recommendations regarding the management practices necessary to maintain the volume growth in China's forest ecosystems.

Keywords: Stand volume growth, Stand origin, Plant functional type, National forest inventory data, Random forest algorithms

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Received: 21 January 2022
Revised: 13 March 2022
Accepted: 20 March 2022
Published: 21 April 2022
Issue date: June 2022

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Acknowledgements

This work was supported by the Major Program of the National Natural Science Foundation of China(No. 32192434), the Fundamental Research Funds of Chinese Academy of Forestry (No. CAFYBB2019ZD001) and the National Key Research and Development Program of China (2016YFD060020602). We thank our colleagues, Yanyan Ni, Yu Tian, for their assistance in providing relevant factor data and data sorting. We thank Shuyi Guo, Rui Wang, staff of the Academy of Forest Inventory and Planning, National Forestry and Grassland Administration, for help with data provision. We also thank the Zigui Forest Ecosystem Research Station for their help.

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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