| Forest spatial structure, which decides the forest diversity and habitat, affects the functions of the forest ecosystem, and restricts the competition situation and spatial niche of forest. It determines the stability and development direction of the forest ecosystem, to a certain extent. Based on the DBH weighted Voronoi diagram method that can determine the reference tree’s neighborhood groups of trees, this paper took the24-year-old Cunninghamia lanceolata non-commercial forest in Fushou State-owned Forest Farm as the study area, by forest sustainable management and close-to-nature forest management thought as the theoretical guidance, calculated mingling, neighborhood comparison, aggregation index, storey index, and open degree, and quantitatively analyzed it’s characteristics of the stand spatial structure. The main contents and conclusions were as follows:(1) Analysis on the distribution pattern of tree positions, based on the Voronoi uniform angle index.1000random distribution of plots with1hm2permanent (100m×100m) each one, were simulated and analyzed. And the standard angle of the uniform angle index based on Voronoi diagram was formulated by360°(n+1). The critical value for the identification of tree random distribution pattern was discussed within the interval μ±3σ. The mean value of the uniform angle index for the random case was defined by the bounds [0.327,0.357]. It can be inferred by the definition of the uniform angle index that a Wv value of less than0.327was most likely from a regular distribution; values exceeding0.357were most likely from a clumped distribution.(2) Statistical analysis on the stand spatial structure index. There was difference between each spatial structure index calculated by different methods of determining basic stand spatial structure unit, but the difference was not apparent, and the three methods are independent. Determining the basic stand spatial structure unit based on weighted Voronoi diagram was a new method which was different with the methods based on4neighbor trees and Voronoi diagram.(3) Analysis on forest spatial structure of the Cunninghamia lanceolata non-commercial forest. There were twelve kinds of different sizes of the spatial structure unit in this community, and the most common phenomenon was that the reference tree had five close neighboring trees. The average mingling of stand was0.23, which indicated the simple spatial allocation and poor mixing of different tree species. The distribution of neighborhood comparison based on DBH, changed with a fluctuant pattern, and the stability of species in the arborous layer was good. The average Voronoi uniform angle index and aggregation index of the stand were0.344and1.06. The individuals of tree presented the succession trend from regular distribution to random distribution. The average storey index of stand was0.24. The spatial configuration was relatively simple in the vertical space. The average open degree of stand was0.23.Thus, the stand was relatively crowded and hadn’t adequate growing spaces.(4) Regulation measures of the Cunninghamia lanceolata non-commercial forest in the stand spatial structure. The physiognomy of this Cunninghamia lanceolata non-commercial forest was simple, and the species of the forest was relatively single. The proportion of single species was too large, so the spatial structure characteristics of Cunninghamia lanceolata basically represented the state of the spatial structure of the whole community. In order to eliminate the disadvantages of this stand, such as, the low mingling, the unreasonable distribution of neighborhood comparison, the uniform distribution pattern, the simple vertical stratification structure, and the insufficient space, some regulation measures in optimizing the stand spatial structure were took by forest thinning and replanting native hardwood species, which can improve forest biodiversity and increase the stand stability. |
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