Multivariate Distribution of Spatial Structure of Pinus taiwanensis Plantation under Different Densities in the Transition Zone from North Subtropical to Warm Temperate Zone

Purpose The aim of this study was to explore the spatial structure characteristics of Pinus taiwanensis plantation under different stand densities in in the transition zone from north subtropical to warm temperate zone, providing a basis for the optimization and adjustment of the spatial structure of coniferous forests in the climate transition zone.

Methods Taking the P. taiwanensis plantations in the state-owned Shangcheng Huangbai Mountain Forest Farm in Xinyang City, Henan Province as the research objects, the spatial structure units were determined by the nearest neighbor method, and the differences in the multivariate distribution characteristics of the spatial structure under different stand densities were analyzed by using the complete mingling degree, size ratio, uniform angle index, and stand layer index.

Results According to the zero-order distribution, the stands with low density had the best degree of mingling and the best vertical structure, while the stands with medium density had the best degree of tree size differentiation and a relatively good distribution of stand density. As shown by the first-order distribution, the stands with low density had the highest degree of mingling and the richest vertical structure, and the stands with medium density had the best distribution state. From the perspective of the second-order distribution, the vertical structure of the three stands was similar and moderately mixed, and the low density stand was dominant and unevenly distributed; the medium density stand was randomly distributed in dominant state; and the high density stand showed random distribution in the mean state. As indicated by the third-order distribution, the three density stands were moderately mixed. The proportion of dominant trees with uneven distribution in low density stands was the largest; the proportion of dominant trees randomly distributed in medium density stands was the largest, and its vertical structure was the most complex; among the high density stands, the trees in the middle state of random distribution accounted for the largest proportion. Quaternion distribution showed that most of the vertical structure complexity of trees with the same distribution pattern was moderate, and the degree of mingling was mostly moderate mingling at the same full mingling degree and size ratio of different density stands.

Conclusion The mixed degree of medium density P. taiwanensis plantation is high, showing a random distribution pattern, the vertical structure is complex, the proportion of dominant trees is the highest, and the stand structure of plantation is the best. The structure of low and high density P. taiwanensis plantations is poor, and it can be properly nurtured and updated to optimize their stand structure in the future.