Diversity And Spatial Distribution Pattern Of Regeneration Tree Species In Castanea Seguinii-Quercus Serrata Broad-Leaved Mixed Forest

In this study,the deciduous broad-leaved mixed forest in Mazongling Forest Farm was taken as the research object.By setting up a 60m×60m fixed sample plot and using the adjacent grid method to investigate the young tree regeneration in the sample plot,the diversity characteristics,spatial distribution pattern,interspecific association and niche of the main regeneration tree species were analyzed in order to improve the forest regeneration ability,improve the underforest vegetation structure,enrich the stand species diversity and predict the future succession development trend of the stand,and to provide a scientific theoretical basis for the management of local secondary forest.The main conclusions are as follows:(1)The forest type investigated in the sample plot is the natural deciduous broad-leaved mixed forest with the dominant tree species such as Castanea seguinii,Quercus serrata,and Platycarya strobilacea.There are 26 species and 1307 trees with a diameter at breast height≥1 cm in the sample plot,belonging to 16 families and 21 genera.The dominant families are Quercus and Castanea of the Fagaceae.There are 23 species of mature trees in the arbor layer,with a total of 487 trees,and 26 species of saplings in the regeneration layer,with a total of 820 trees;the dominant populations with the important value of the arbor layer greater than 10%were Castanea seguinii,Quercus serrata,and Platycarya strobilacea,and the dominant populations with the important value of the regeneration layer greater than 10%were Styrax japonicus,Lindera glauca and Diospyros lotus.By comparing the Margalef richness index(3.56),Shannon-Wiener diversity index(2.57),Simpson index(0.90),Pielou evenness index(0.82)of the arbor layer and the Margalef richness index(3.71)of the renewal layer,Shannon-The results of Wiener diversity index(2.42),Simpson index(0.87),and Pielou evenness index(0.74)showed that the values of each index were relatively high,the difference was not significant,and the species were relatively abundant.The distribution of total tree diameter at breast height in the sample plot is approximately inverted"J"curve,with a large number of saplings and good regeneration status,and the average DBH of the stand is 7.2cm.Among the main tree species,the number of renewals of Castanea seguinii and Platycarya strobilacea are less,and the populations tend to decline.The number of new generations such as Styrax japonicus,Lindera glauca,Diospyros lotus and Quercus serrata has an increasing trend.With the succession of the community,these light-loving and shade-tolerant or shade-tolerant tree species will gradually enter the arbor layer to replace the chestnut,fragrant and light-loving tree species in the future.(2)Through the analysis of the spatial distribution pattern of the population in the sample plot,it is concluded that under the complete random model(CSR),the stand is mainly aggregated distribution,while under the heterogeneous Poisson model(HP),the stand is mainly random distribution,and only shows aggregate distribution on a small scale.The point pattern analysis of the five main regeneration tree species in the stand,Styrax japonicus,Lindera glauca,Diospyros lotus,Quercus serrata and Castanea seguinii,showed that no matter under the CSR model or under the HP model,the performance was small.The scale aggregation distribution,with the increase of the scale,gradually presents a spatial distribution pattern of random distribution.However,after removing the habitat heterogeneity,the scale range of the aggregate distribution of all saplings was reduced,only in the smaller scale range of 0-5m,and the other scales showed random or uniform distribution.It shows that the small-scale aggregation is caused by its own biological characteristics,such as the limitation of seed dispersal,while the large-scale aggregation is due to the influence of habitat heterogeneity.The spatial associations between sapling-sapling species pairs composed of major tree species in the community were dominated by irrelevance and negative correlation,and the spatial associations between sapling-adult species pairs were mainly irrelevant.(3)The niche breadth,niche overlap and similarity ratio of 17 regeneration tree species with important values greater than 1 in the plot were analyzed,and it was concluded that the niche breadth(BL)of Levins was in the following order:Lindera glauca>Euscaphis japonica>Diospyros lotus>Styrax japonicus>Quercus glandulifera>Symplocos sumuntia>Dalbergia hupeana>Dendrobenthamia japonica>Castanea seguinii>Meliosma veitchiorum>Photinia beauverdiana>Bothrocaryum controversum>Kalopanax septemlobus>Carpinus turczaninowii>Cerasus serrulata>Hamamelis mollis>Acer elegantulum.The Shannon niche breadth(BS)order is:Lindera glauca>Euscaphis japonica>Diospyros lotus>Quercus glandulifera>Styrax japonicus>Symplocos sumuntia=Dalbergia hupeana>Dendrobenthamia japonica>Castanea seguinii>Bothrocaryum controversum>Photinia beauverdiana>Meliosma veitchiorum>Kalopanax septemlobus>Carpinus turczaninowii>Hamamelis mollis>Cerasus serrulata>Acer elegantulum.It can be seen that the order of the BL and BS values of the sapling populations is basically the same.The populations with larger niche widths indicate that they have a wider ecological adaptation range.The bit overlap value is also larger.The larger the niche overlap value,the greater the niche similarity ratio,and the result trend of the niche similarity ratio and the niche overlap value is not much different.(4)Through the interspecific association study of 17 regeneration tree species with important values greater than 1 in the plot,the variance ratio method and statistic W were used for analysis,and it was concluded that the overall connectivity of the update layer community showed a weak negative correlation.The results ofχ~2 test,AC,PC and OI index showed that most of the regeneration tree species were not strongly correlated.In the results of Pearson correlation coefficient test and Spearman rank correlation coefficient test,the species pairs with positive correlation were less than those with negative correlation,and most of them were not strongly associated,which was basically consistent with the results ofχ~2 test.The difference was that the significant rate of species pairs of Pearson correlation coefficient test and Spearman rank correlation coefficient test was higher than that ofχ~2 test.It can be seen that the overall connection of the young tree population is not strong,most of the regeneration tree species are not significantly associated with each other,showing the characteristics of independent distribution,and the community is in a relatively stable succession stage.