Study On The Structure Of Dominant Species And Interspecific Relationships Of Karst Vegetation In Central Guizho

Karst is a geomorphic type widely distributed in the south of China.Guizhou is a typical karst geomorphic Province,which distributes the complete karst ecosystem in China.The karst vegetation in the central area of Guizhou is mainly evergreen and deciduous broad-leaved mixed forest formed by evergreen and deciduous tree species as the dominant species.The dominant population formed by these dominant tree species regulates and affects the structure and function of karst forest vegetation,but the quantitative structure characteristics of dominant tree species and their functional relationship with main associated tree species are still unclear.Therefore,It is of important theoretical and practical significance to study the quantitative and structural characteristics of dominant populations of karst vegetation in central Guizhou and to explore the relationship between dominant tree species and associated tree species for revealing the species coexistence mechanism of karst vegetation and ecological restoration of degraded karst vegetation.This paper investigates 53typical karst forest vegetation sample plots in Xiayun town,Gaofeng town and Machang town in Pingba District of Anshun City.And the stem level structure,height level structure and distribution pattern of three dominant populations of Platycarya longipes,Itea yunnanensis and Carpinus pubescens Burk are statistically analyzed by the population quantitative ecology method.Then select the top 15 main tree species with important values for niche and interspecific connectivity analysis.The main results are as follows:（1）The age structure and height structure of Platycarya longipes,Itea yunnanensis and Carpinus pubescens Burk population in the study area are all growth types.The dynamics of the community height level is basically the same as that of the dominant species,and the number of individuals gradually decreases with the increase of the tree height and becomes stable at the height level 5.The high-level instability rate of the dominant species is basically greater than 0.The population instability rate and community instability rate are also greater than 0.The results show that the community is of growth type.（2）Platycarya longipes is evenly distributed in age class 1 and age class 2,and the other age classes are clustered,while the population is evenly distributed.Itea yunnanensis is evenly distributed in age class 1,and the other age classes are clustered,while the population is evenly distributed.Carpinus pubescens Burk is evenly distributed in age class 2,and the other age classes are clustered,while the population is evenly distributed.The results show that the aggregation degree of dominant populations gradually increases with the increase of age class,and the community tends to be stable.（3）Study on the niche of the dominant tree species and the main associated tree species finds that Platycarya longipes is the specie with the largest niche breadth.The species with the smallest niche breadth of Shannon-wiener is Quercus phillyraeoides,while the species with the smallest niche breadth of Levins is Corylus heterophylla.The distribution of species pairs with niche similarity in the community is mainly concentrated between 0.15 and 0.45,which is at a moderate level.Species with large niche breadth have higher niche similarity.Zanthoxylum bungeanum and Stachyurus obovatus have relatively high niche similarity with other species,and the two species have a large niche overlap value.However,the niche of Quercus phillyraeoides and Pyracantha atalantioides,Quercus phillyraeoides and Corylus heterophylla has basically no overlap.The niche overlap values of various pairs of communities are mainly concentrated between 0-0.012(L_ih)and 0-0.008(L_hi).The species pair with the highest niche similarity is the species pair composed of two dominant species,Platycarya longipes and Itea yunnanensis（0.5345）.The two species pairs with the largest niche overlap values are Stachyurus obovatus and Corylus heterophylla(L_ih=0.0153),Stachyurus obovatus and Pyracantha atalantioides(L_ih=0.0153).The results shows that the niche overlaps between main species are generally small.And niche similarity is positively correlated with niche breadth.（4）The overall association of dominant populations in this area is significantly positive correlation.Chi-square test results show that the number of positive-link species is more than that of negative-link species.The AC association coefficient results show that there are many species pairs with extremely significant positive association with Zanthoxylum bungeanum and Stachyurus obovatus,and species pairs with significant negative association with Quercus fabri and Corylus heterophylla.The results of OI test of connection coefficient show that the species pairs composed of Platycarya longipes,Lindera communis and Zanthoxylum bungeanum have greater connection（OI≥0.7）,while the Quercus phillyraeoides and Corylus heterophylla,Quercus phillyraeoides and Pyracantha atalantioides have less connection（OI≤0.1）.The Pearson test shows that there are more species pairs with extremely significant positive association with Carpinus pubescens Burk and Prunus tomentosa.There is a extremely significant negative association between white Quercus fabri and Ligustrum lucidum.The results of the Spearman rank test shows that there are more species pairs with extremely significant positive association with white Quercus fabri,and more species pairs with extremely significant negative association with Prunus tomentosa.The results show that the interspecific association in the community is close,and the community is in a relatively stable stage.In summary,the community has a stable growth trend.With the development of succession and the growth of the age class of dominant species,the degree of population aggregation gradually increases and the community structure becomes more stable.Niche overlaps among major species are mostly small,and niche similarity is positively correlated with niche width.The interspecific connectivity of the dominant species in this community is relatively close,that is,the community is in a relatively stable stage.