Study on the canopy structure and light distribution of Hippophae rhamnoides at different ages

The canopy structure of seabuckthorn has a profound effect on its light environment and ecological function with the dynamic evolution of stand age. To quantitatively analyze the driving mechanism of stand age and canopy structure on light distribution, PAR and key canopy structure parameters (LAI, PALe, OmegaE and Gap Fraction) were measured simultaneously along the vertical profile (bottom, middle and top) of 3-, 4-, 8- and 11-year-old seabuckthorn plantations by using TRAC. Two-way analysis of variance, structural equation modeling (SEM), redundancy analysis (RDA) and a variety of machine learning models were used for analysis. The results revealed that stand age and relative height had significant effects on all canopy parameters and PAR (p< 0.001). SEM revealed that the unit Gap Fraction had the strongest direct positive effect on PAR (b = 0.826), whereas the LAI indirectly affected PAR mainly by negatively regulating the unit Gap Fraction (b = -0.628). RDA revealed that stand age was the dominant factor driving the variation in canopy structure (LAI, PALe), with an independent inter-pretation rate of 31.72%. The random forest model performed best in the classification task of stand age inversion on the basis of canopy characteristics (accuracy rate of 85.19%). This study provides an important theoretical basis and quantitative tool for optimizing light distribution, coordinating growth and fruit-ing, and realizing the coordinated improvement of ecological and economic benefits through canopy structure management (such as reasonable pruning to maintain an appropriate Gap Fraction) of seabuckthorn economic plantations.