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Scientia Silvae Sinicae ›› 2022, Vol. 58 ›› Issue (8): 76-88.doi: 10.11707/j.1001-7488.20220808

• Research papers • Previous Articles     Next Articles

Evaluation of Stand Spatial Structure of Cunninghamia lanceolata Public Welfare Forest by Using Structural Equation Model

Wenfei Zhao1,Xiaoyu Cao1,2,*,Zhengchang Xie1,Yifan Pang1,Yaping Sun1,Jiping Li1,2,Yongjun Mo1,Da Yuan1   

  1. 1. College of Forestry, Central South University of Forestry & Technology Changsha 410004
    2. Key Laboratory of Managment and Testing of Forest Resources in Southern China, National Forestry and Grossland Administration Changsha 410004
  • Received:2022-03-21 Online:2022-08-25 Published:2022-12-19
  • Contact: Xiaoyu Cao

Abstract:

Objective: The spatial structure of Cunninghamia lanceolata public welfare forest was comprehensively evaluated, and the current situation of spatial structure of different age groups was determined, in order to provide theoretical bases for formulating accurate and feasible stand spatial structure optimization and management measures. Method: Taking the Cunninghamia lanceolata public welfare forest in Lutou experimental forest farm of Pingjiang county, Hunan Province as the research object, based on the measured data of 30 sample plots, the stand spatial structure unit was determined by four adjacent trees.Taking the totalmingling degree, uniform angle index and spatial density index as the observed variables of the horizontal spatial structure of endogenous latent variables, taking the storey index, open degree and angle competition index as the observed variables of the vertical spatial structure of endogenous latent variables, and taking stand spatial structure as the exogenous latent variables, the stand spatial structure evaluation structural equation model was constructed. The path coefficient output from the structural equation model was normalized to determine the weight of each index. On these bases, the stand spatial structure was comprehensively evaluated. Result: 1) For the structural equation model of the evaluation of stand spatial structure, the normed Chi-square (χ2/df) was 1.708, which was between 1-3. The values of comparative fit index(CFI), non-normed fit index(NNFI) and incremental fit index(IFI) were 0.944, 0.924 and 0.946, respectively, which were all greater than 0.90. All the fitting indexes conformed to the appropriate reference value, and the overall fitness of the model was good. 2) The weights of horizontal spatial structure and vertical spatial structure of endogenous latent variables were 0.5229 and 0.4771 respectively, and their effects on the stand spatial structure of exogenous latent variables were roughly the same. The spatial density index of the observed variables was the key factor affecting the horizontal spatial structure. The open degree and competition index were equally weighted, and the both were key factors affecting the vertical spatial structure. 3) The comprehensive scores of young, middle and near-mature Cunninghamia lanceolata forests were 0.3781, 0.4526 and 0.3775 respectively. The stand spatial structure grades of the three age groups were in grade Ⅱ and Ⅲ. Overall, the spatial structure of Cunninghamia lanceolata public welfare forests in the study area did not reach the ideal state. The spatial structure of the forest was poor, and the mingling degree of tree species was low, being close from zero degree mixing to weak mixing state. The degree of crowding was medium, and the light transmission conditions of trees were general. The forest layer structure was single, but the competition intensity among trees was weak, and the spatial distribution pattern was good, which was in the state of uniform to approximate random distribution. Conclusion: Both the horizontal spatial structure and vertical spatial structure of the stand were the key factors affecting the stand spatial structure. The results of the structural equation model further found that the spatial density index was the most important factor affecting the stand horizontal spatial structure. The open degree and competition index were the important factors affecting the stand vertical spatial structure. Therefore, in order to improve the overall stand spatial structure in the study area, comprehensive management measures such as multispecies replanting and singleplant tending-thinning should be adopted. From the evaluation results of the stand spatial structure of the three age groups of Cunninghamia lanceolata ecological public welfare forests in the study area, it objectively reflected the current status of the stand spatial structure, indicating that the idea of using the structural equation model to evaluate the stand spatial structure was scientific and reasonable, and it was expected to provide a new idea for stand spatial structure evaluation.

Key words: Cunninghamia lanceolata public welfare forest, stand spatial structure, structural equation model, index weight

CLC Number: