Single tree competition index is the basis for researching tree competition relationship.For describing tree competition intensity accurately,many scholars are still devoting themselves to constructing and improving competition index.In 2013,Hui Gangying proposed forest competition index based on intersection angle which utilized intersection angles between objective tree and it,s neighbors to describe the over shading and the lateral extruding of the objective tree.Three 60m x 60m spruce-fir plots whose conditions are basically identical were set in Jingouling Forest Farm,Wangqing County,Jilin Province.First,Based on forest competition index based oh intersection angle,the correlation of all types of competition indexes with the tree size factor DBH is judged with correlation and regression analysis method and evaluate the result in natural spruce-fir forest in Jingouling Forest Farm,and then we choose the optimal forest competition index.Second,The total competition of three stands and the competitive relationships among dominant tree species were then examined using optimum tree competition index that describe intra-and inter-specific competition from the above and sides of individual tree crown.Finally,a thiessen polygon was taken into a regeneration research unit,and mean DGH、mean height and number of regeneration were statisticsed in every thiessen polygon;finally,to explore basic characteristics of regeneration with different competition intensity,competition intensity was divided into some classes,and mean DGH、mean height and number of regeneration were statisticsed again under different competition class.All aboves provide theoretical basis for management the and the gj’owth regeneration in natural spruce-fir forest.The results of the study are as follows:(l)Trees density in plot 1 and plot 2 is nearly same,plot 3 is a little small(the numbers of trees whose DBH is greater than or equal to 5cm in plot 1、2、3 are 420、443、249 respectively);the difference of the indices such as average diameter at breast height,average height,average crown size and so on of arbor in the three plots trees is small;arbor tree species in three plots are mainly Abies nephrolepis,Picea koraiensis,Finus koraiensis,Betula costata,Betula platyphylla and Acer mono et al,tree number decreases gradually along with the increase of diameter class,forest community is in small age.density of regeneration of plot 2 1s the largest,second is plot 1,third is plot 3(the numbers of regeneration whose height is greater than or equal to 0.3m in plot 1、2、3 are 857、1417、549 respectively);regeneration tree species in three plots are mainly Abies nephrolepis,Picea koraiensis and Acer mono(the percentages of the three regeneration tree species in plot l.2n 3 are 91.60%n 89.13%、87.98%),regeneration DGH in three plots is mainly in A、B、C class(the percentages of the three DGH class in plot 1、2、3 are 84.60%、82.22%、82.15%),regeneration height in three plots is mainly in a、b、c class(the percentages of the three regeneration height class are 90.78%、92.52%、92.17%).(2)d_a_CI1 is the optimal forest competition indexThe correlation of the optimal competition index with the tree size factor DBH is higher than before,the optimal competition index can describe competition among trees better;The tree size factor DBH is not only related with lateral extruding,but also related to over shading;The number of neighbors of objective tree varies with stand condition,all kinds of competition indexes with thissen polygon have closer correlation with tree size factor DBH in plot 1,but all kinds of competition indexes with 8 neighbors have closer correlation in plot 2 and plot 3.The optimal competition index having uncertain values is still non-dimensional.However,the conclusion is still right that there is positive correlation between competitive pressure of the objective tree and it’s size factor DBH.It remains to be further researched that if the optimal competition index is applicable to other forest stands for competition analysis.(3)Take 1 ha plotl for example to define the competitive relationships among dominant tree species in natural spruce-fir forest.The results indicated three dominant tree species in this mixed-species community,Abies nephrolepis,Picea koraiensis and Pinus koraiensis.Abies nephrolepis,Picea koraiensis,Pinus koraiensis,Betula costata,Tilia amurensis,Acer tegmentosum and Betula platyphylla were the main competitors of the dominant tree species,while Abies nephrolepis was the major competitor for all three dominant tree species(1412.48),followed by Picea koraiensis(439.17)and Pinus koraiensis(245.28),the latter two generally had side squeeze effect(64.9%,65.2%and 66.0%of the total competition for the three dominant tree species,respectively).The level of side and above competiiton decreased with individual tree DBH(diameter at breast height);the percentage of side competition was nearly equal to that of above competition in small trees and increased with tree size reaching nearly 100%in large canopy trees.Among the three dominant tree species,inter-specific competition was more intense than intra-specific competition(about 58.4%,87.1%,83.7%of the total competition for the three dominant species),both of which decreased with individual tree DBH.These results,along with the management of the mixedwood forest for biodiversity,and the wood quality of the three dominant tree species,and the conditions of sampling area,indicate a low thinning targeting small and intermediate diameter class Abies nephrolepis to reduce side and above competition among Abies nephrolepis with other tree species.Study the whole competition of each stand,we finally concluded that the whole competition mainly relate to arbor numbers,the total competition in plot 2>plot 1>plot 3,interspecific competition,lateral extruding competition and over shading competition have the same regulation,but the intraspecific competition has the contrary regulation,intraspecific competition in plot 2<plot l<plot 3,this suggests that the plot 3 has more same tree species.The three natural spruce-fir forests are the mainly subjectived with extruding competition or interspecific competition.(4)Take a thiessen polygon was taken into a regeneration research unit,the change of regeneration mean DGH、mean height and number of regeneration with different competition classes of objective tree in spruce-fir forest are broadly in line with the change of three function(first decrease,and after increase,then decrease).When competition class is about Ⅴ class,mean DGH、mean height and number of regeneration are of general maximum;when competition class is about Ⅰ、Ⅱ class,mean DGH、mean height and number of regeneration are bigger also.But,when the intensity of competition in class Ⅰ and class Ⅱ,the stand density is small too,if we simply want cultivate regeneration seeding,we can choose this competitive strength range,if we want to promote natural regeneration in the mixed forest,we need to keep the competition strength around to Ⅴ class. |