Multivariate distribution of spatial structure parameters of Populus davidiana-Betula platyphylla secondary forest

  Objective  This paper aims to systematically describe and analyze the spatial structure characteristics of Populus davidiana-Betula platyphylla secondary forest of two origins (natural regeneration of failed afforestation area and fire slash) in Jingouling Forest Farm, Jilin Province of northeastern China using multivariate distribution of stand spatial structure parameters, so as to provide powerful means for forest management and optimization of stand structure and promote forest succession.

  Method  Six sample plots (30 m × 30 m) of trees were surveyed and located. RStudio forestSAS package was used to calculate the spatial structure parameters, including uniform angle index, neighborhood comparison, mingling degree and crowding degree of each sample plot, and calculate the frequency distribution of each origin, using Origin 2018 to establish multivariate distribution map of structural parameters.

  Result  The average values of Populus davidiana-Betula platyphylla secondary forest showed that the two kinds of forests were in the middle growth state of aggregation distribution and good mixture, while origin Ⅱ was denser than origin Ⅰ. The univariate distribution showed that most of the trees in the forests were randomly distributed, well mixed, denser or very denser, and each neighborhood comparison occupied nearly. In origin I, Populus davidiana grew well, most of them were in the dominant and sub-dominant growth state, while Betula platyphylla, Fraxinus mandshurica and Betula costata were generally in the middle growth state. In origin II, Populus davidiana and Betula platyphylla had more dominant trees and less inferior ones, and they grew well in general. Among the univariate distribution, trivariate distribution and quadrivariate distribution, it showed that under various combinations of structural parameters, most of the trees were well mixed or randomly distributed.

  Conclusion  Compared with the traditional use of structural parameters of average values and univariate distribution, the use of multiple distribution to describe the structural characteristics of Populus davidiana-Betula platyphylla secondary forest is an effective method to optimize its management and structure, which contains more abundant and clear information. At the same time, it is also an operable method for selection of cutting woods.