Study On The Stand Spatial Structure Of Broad-leaved Mixed Forest Based On Voronoi Diagram

The forest spatial structure restricts the normal exertion of all the functions of forest ecosystems,especially seriously affecting the competition of habitat resources and the growth space between single trees,and also plays an important role in the long-term stable and healthy development of forest ecosystems.This study aims to explore the natural broad-leaved mixed forest in Lingnan Nature Reserve of Xiuning County,Anhui Province.Seven broadleaf mixed forest plots were set up in the study area by using total station(Southern NTS-320)closed wire measurement method.The size of the plots was 24 m×24 m;the area of forest land was 576 m2.Based on reference data of the size ratio(Ui),the mixing degree(Mi)and the angle scale(Wi)which were calculated by 4 species competing directly for the basic structure of space adjacent to the wood,and the basic structural unit of the forest which constructed based on the Voronoi diagram,the forest space separation parameters(Mci),spatial competition index(UCI),spatial distribution pattern parameter(Wvi)and forest light transmission parameters(Ki)were calculated and analyzed,and the comprehensive index(FSSI')of forest spatial structure evaluation and the distance parameter(FSSD ')between the forest spatial structure and the ideal model were constructed.After investigation and analysis,the conclusions as follow:1.When constructed the basic spatial structure unit based on the Voronoi diagram,the number of direct competition woods is equal to the number of sides of the Voronoi diagram in the central wood,and the direct competition area of the central wood is the area of the Voronoi diagram.The results showed that the 4-6 strains of direct competition wood were the most common,and the number of average direct competition adjacent wood was 5.64 in the basic structural unit.2.According to the analysis of the isolation parameters,it can be seen that Mci of the whole forest stands in each sample plot which based on the Voronoi diagram was concentrated in the moderate or intensity mixed state and the spatial structure of the forest was more complicated;the diversity degree of forest was higher;and it tended to a stable trend,which was very consistent with the results of four direct competition wood.However,research found that there were some different in the two methods according to different species to calculate.3.UCIi of each sample plot was distributed in the interval(0.25,0.50),indicating that the growth of the stands was moderate and the distribution of leaf diameter was uniform,and the growth of stand was not obvious.This is consistent with the results of Ui of 4 direct competition woods in qualitative analysis.Both methods showed that there was no absolute dominant species in the sample,and the growth of the whole forest tree tends to be stable.4.The average distribution pattern of every sample plots,which analysed by stand structure unit which constructed based on the Voronoi diagram and which constructed by four direct competition adjacent woods,is the cluster distribution.The structural units and the random structural units in the stands are far less than the structural units of the cluster,which has a certain relationship with the shorter enclosure time of the nature reserve and the pre-enclosure labor intervention.5.The opening degrees of No.1 and No.3 sample plots were 0.42 and 0.49,respectively,which indicating that the average stand of these two plots was sufficient.The opening degree values of No.1,No.4,No.5,No.6 and No.7 sample plots were distributed in the interval(0.3,0.4),which indicating that the average growth space of these plots was basically sufficient.In terms of the whole forest stand,the overall growth space was basically enough and the forest light transmission conditions were good.According to the analysis of different species,it was found that the growth of the main tree species had a good light transmission,and the light conditions were bad in the associated tree species.6.In this paper,a new comprehensive model of forest spatial structure FSSI is constructed.The concrete formula as follow:FSSI' =[Mci ×(1-UCIi)×2.9240Wvi]0.3333,Wv?0.342[Mci×(1-UCIi)×1.5198(1-Wvi)]0.3333,Wv>0.342Where0?Mci,UCI,Wvi?1,0?FSSI'?1,the higher the FSSI value,the better the spatial structure level.In the "three-dimensional scatter distribution map”controlled by three structural parameters,the distance model(FSSD ')of the spatial structure and ideal structure of the stand was redefined based on the trend which approached or departure the ideal location point and structural position of stand structure,the formula as follow:FSSD' = ?(Mci-1)2+UCIi2+(Wvi-0.342)2Where0<Mci?UCI?Wvi?1;0?FSSD'?1.63,the smaller the value,the closer the stand structure is to the ideal structure.The study found that FSSI 'has a very significant linear relationship with FSSD',FSSI'=-1.637-FSSD'+1.025,R2=0.980(P<0.01),the degree of model fitting is good.Therefore,both FSSI' and FSSD' can analyze the spatial structure of forest stand and dynamic changes quantitatively.Comparison of FSSI 'and FSSD' found that the spatial structure of the stands was at a lower level II,which had a great relationship with the distribution of dissimilarity in varying degrees.Forest spatial structure optimization degree:plot No.6>plot No.7>plot No.5>plot No.3>plot No.4>plot No.2>plot No.1.