An Analysis Of The Coupling Relationship Of Stand Characteristic Factors Based On Structural Equation Model

In the process of the forest management, grasping the status of forest resources of forest stand growth is very important to macro-management of forest resources. Site conditions, stand structure and trees diversity have a significant impact on the forest stand growth, and analyzing the relations between them effectively and quantitatively is conducive to operation and management of forest resources.In order to find out the relationships of stand characteristic factors, the structural equation model of the site condition - stand structure-trees diversity - stand volume and site condition-structure of upper canopy layer - trees diversity of upper canopy layer - structure and trees diversity of lower canopy layer are built taking secondary multiple species forest beside Ashi River as example. The results show that:Site condition, stand structure and tree diversity have a positive effect on the whole stand volume. The order of influence coefficient is stand structure, site condition, trees diversity, total path coefficients are 0.78,0.39, 0.11. Site condition has an obvious effect on stand structure and tree diversity. The better site condition there is, the better stand structure and trees diversity they have. The increasing of site condition and stand structure is also contributed to the stand volume. Site condition has a positive impact on stand growth, most parts of which is formed indirectly by improving forest structure and trees diversity.Site condition, structure of upper canopy layer and trees diversity of upper canopy layer have a negative effect on structure and trees diversity of lower canopy layer,. The order of influence coefficient is Site condition, structure of upper canopy layer, trees diversity of upper canopy layer, total path coefficients are -058, -0.55, -0.31. The main factors which affecting the growth of lower canopy layer is light, water and heat. Better site condition is contributed to the growth of the upper canopy layer. Due to shielding effect of the upper canopy layer, the lower canopy may get less light, water and heat. It is not conducive to the growth of lower canopy layer. The slope position in the site condition has a significant effect on the upper canopy layer. The lower slope position is, the higher average height, crown area and species diversity are. They intensified the competitive effects of the lower canopy layer.The structural equation model of the coupling relationship of stand characteristic factors we have made has a good interpretation of the main influence factors of stand growth. Natural systems are essentially complex. Compared with traditional multivariate methods, fully understanding natural systems requires the capacity to examine simultaneous influences and responses among multiple interacting factors. Structural equation model (SEM) could specify the causal or dependent relationships among variables using the prior knowledge of researchers before conducting relevant experiments, i.e. initial models. SEM could not only identify the individual path coefficient for each relationship, but also estimate the whole model fit to determine whether to revise the initial models.