Prediction of stem radial growth in natural stands and plantations of Pinus sylvestris L. using crown morphometry available for terrestrial lidar scanning and taking into account the multicollinearity of the factors

The crown of a tree is important in studying the physiology of the forest canopy and modeling its dynamics, and the dependence of the radial growth of the stem on the morphometry of the crowns has been established. However, the relationship between the structural characteristics of the crown and the growth rings is poorly understood due to the high complexity of analyzing the crown structure using classical approaches. Terrestrial lidar scanning offers anew perspective for quantifying crown structure in 3D format, which can significantly contribute to understanding plant adaptations to the environment and their structural and functional responses. The purpose of this work was to develop predictive models of radial stem growth in relation to crown morphometry available for terrestrial lidar scanning. The research was carried out in the Aman-Karagaj forest in the conditions of the dry steppe of the Turgaj Depression, where 37 sample plots were established in pure Pinus sylvestris L. forests, on which 300 model trees were taken, including 190 in plantations and 110 in natural forests. The optimization of the model structure is performed according to the condition of multicollinearity of independent variables – crown diameter, crown length and crown ratio. It was found that with the same crown morphological structure, the cross-sectional stem area increment in natural stands is 38–46 % lower in relation to plantations, and the radial growth is 17–34 % lower, respectively. The models of stem cross-sectional area increment turned out to be more informative compared to the models of annual radial growth (65–73 % vs. 45–58 %), and the ontogenetic legacy of crown morphological structure is expressed to the greatest extent in increments over 10, but not over 5 years, which is confirmed by comparing the coefficients of determination (0.58–0.73 vs. 0.45–0.65).

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