Improvement And Application Of Voronoi Diagram In Stand Spatial Structure Optimization

The close neighboring trees of reference tree was fixed for 4 in the traditional method of determining the reference tree’s neighborhood groups of trees, and the spatial structure unit can determined flexibly based on the ordinary Voronoi diagram method, but the ordinary Voronoi diagram method only considered the location of trees without considering the attributes of trees, the reference tree’s neighborhood groups can not fully reflect the spatial relations of trees.To analyze the stand spatial structure characteristics accurately, the Cunninghamia lanceolata non-commercial forest in Fushou State Forest Farm in Hunan province was taken as the study object, and DBH(diameter at breast height), tree height and crown-width were taken as a comprehensive weight to built weighted Voronoi diagram. Then nearest neighbors of the object one was determined and mingling degree, competition index, neighborhood comparison, aggregation index and storey index were calculated based on the weighted Voronoi diagram. And the stand conditions were respectively analyzed by the 5 parameters based on weighted Voronoi diagram. Finally, the stand optimization spatial model was built, the solutions of intermediate cutting and replanting were put forward. The main contents and conclusions were as follows:(1)The weighted Voronoi diagram method considered not only the location of trees but also the attributes of trees, which can accurately reflect the spatial relations of trees. The most common spatial structure unit was the object tree with five close neighboring trees, and spatial influenced region of individual tree increased with the comprehensive weight.(2)The means of mingling degree, neighborhood comparison, aggregation index and storey index calculated based on the ordinary and weighted Voronoi diagram were almost the same, the means of competition index have large difference. The correlation coefficients of mingling degree, neighborhood comparison, competition index and storey index calculated based on the ordinary and weighted Voronoi diagram were greater than 0.8, but the correlation coefficients of aggregation index was only 0.275. 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. Determining the basic stand spatial structure unit based on weighted Voronoi diagram was a new method which was different with the methods based on Voronoi diagram.(3)The average mingling degree of the young stand was0.34, belonging to the transition from weak degree mixed to moderate mixed, the average mingling degree of the middle-aged and nearly-mature stand were 0.17 and 0.23 respectively, both belonged to weak degree mixed, which indicated that the segregation of tree species in Cunninghamia lanceolata stand with three different ages was low. The big difference between the maximum and the minimum of competition index showed the level of competition has different intensity. The average neighborhood comparisons of Cunninghamia lanceolata which is the dominant plant of three different ages stand were 0.5 or so, the stand belonged to the medium competition state. the average uniform angel index of plots of the young stand is above 0.357, these plots presented the transitional type of clumped distribution and random distribution, but the average uniform angel indexes of the middle-aged and nearly-mature stand were below 0.327, the distribution of these stand were random. The vertical structure of the middle-aged was better than the young stand and nearly-mature, but the vertical stratification of three different ages were relatively simple, and the understory was lacked.(4)By choosing mingling degree, competition index, aggregation index and storey index as the adjustment target stand spatial structure, and taking non-spatial structure as the constraint condition, built the stand optimization spatial model, and put forward solving method of the model to determine the solutions of intermediate cutting and replanting, so that the stand spatial structure can achieve the ideal state, and give full play to the functions.