Study on Spatial Structure Characteristics of Broad-leaved Pinus koraiensis Forest at Different Succession Stages in the Xiaoxing'an Mountains

By analyzing the spatial structure characteristics of the four succession stages in the secondary succession of broad-leaved Pinus koraiensis forest, the process and trend of succession can be understood, and suggestions for the restoration and development of secondary forest can be given to speed up the succession process. At the same time, it can also give the idea of reasonable mixed management of plantation. In this paper, natural maple birch secondary forest, secondary broad-leaved forest, secondary coniferous and broad-leaved mixed forest and original broad-leaved red pine forest in the secondary succession sequence of broad-leaved red pine forest in Liangshui Nature Reserve were selected as the research object, and the spatial structure characteristics of forest trees were analyzed by using the univariate and binary distribution of spatial structure parameters (angular scale, size ratio, mixing degree). The results showed that: In the mono-binary distribution, the angular scale of the stand showed a relatively normal distribution, and the frequency was the highest when W=0.5. The average angular scale of the four stages was 0.577, 0.557, 0.634 and 0.589, respectively, and the distribution was mainly light aggregation.With the succession, the aggregation trend increased, and the aggregation degree decreased after the original broad-leaved pine forest. The size ratio of stand in the four succession stages was in the mean state, the proportion of dominant trees in the community fluctuated with succession. In the four succession stages, the trees showed extremely strong mixing, and the proportions of intensity and extreme intensity mixing were 69.94%, 70.08%, 65.56% and 63.64% in turn. The proportion of mixed forest increased first and then decreased with succession sequence. From the perspective of spatial distribution of dominant species in different succession stages, the top five dominant species showed a clustered distribution, and their tree species were highly mixed, but there was a big difference in tree size differentiation between positive pioneer species and shade tolerant species. The changes of the four succession stages of the broad-leaved Pinus koraiensis forest indicate that the angular scale and mixing degree of the trees are larger in the early succession period, and the aggregation degree decreases and the random distribution proportion increases in the later period, especially in the original broad-leaved Pinus koraiensis forest, which is conducive to the long-term and stable development of the community.