Horizontal Spatial Pattern And Dynamics Of Secondary Poplar-birch Forest Community In Changbai Mountains

At the beginning of the 20 th century,the primary forest of Changbai Mountain was strongly disturbed by large-scale industrial logging.The logging site gradually succeeded as a secondary forest or planned as an artificial forest.The forest composition and spatial structure were significantly changed,and the ecological service function was significantly reduced.In order to improve the quality of secondary forests and promote sustainable forest development,this study took fixed monitoring plots of 5.2 ha secondary poplar-birch forest in Changbai Mountain as the research object,based on field survey data in 2009 and 2017,and used spatial point pattern analysis based on different zero models(1)the dynamic changes of population quantity and horizontal spatial pattern of secondary poplar birch forest during 8 years were studied;(2)the degree of population horizontal spatial pattern affected by habitat heterogeneity is analyzed,the optimal ring width was discussed,and the horizontal spatial pattern of each tree species after removing the impact of habitat heterogeneity was analyzed;(3)the effects of density and distance dependence on the horizontal spatial pattern of the population were discussed.The main findings are as follows:1.In the dynamic study of the number of populations and the horizontal spatial pattern,it was found that the number of trees in the forest community has declined in the past 8 years,and the number of deaths of each tree species is proportional to the amount of new growth.Compared with other tree species,the increase and death of shrub species are larger,and the secondary poplar-birch forest is succeeding to broad-leaved Korean pine forest.Overall,the dead and renewed individuals are only positively correlated with small-diameter surviving individuals,and the renewed and dead individuals are negatively correlated.2.In the study of the impact of habitat heterogeneity on the population-level spatial pattern,using mature large trees of different life forms and tree species to test habitat heterogeneity,it was found that each tree species was significantly aggregated,reflecting the importance of habitat heterogeneity in studying spatial patterns.By comparing and analyzing the effects of different ring widths on the horizontal spatial pattern of forest stands,the optimal ring width of this plot was selected to be 3 m.After removing the influence of habitat heterogeneity,the horizontal spatial pattern of most tree species in the 0 – 30 m scale changed from aggregate distribution to random distribution.3.In the study of the influence of density and distance dependence on the horizontal spatial pattern of population,it was found that 14 tested tree species were all affected by density dependence.The occurrence of density dependence is closely related to the abundance of species and the intensity of the same species gathered on a local scale.As the scale increases,the percentage of tree species affected by density dependence gradually decreases.In addition,as the tree diameter increases,the positive correlation with the big tree increases,that is,the middle tree has a more obvious aggregation distribution than the small tree,and tends to be distributed around the big tree.