Community Dynamic And Influencing Factors Of Chinese Fir Plantations In Gutianshan

Forest community dynamics has always been one of the hot issues in the research of forest ecology.The study of forest dynamics was the basis for understanding many ecological processes and was of great significance to understand the changes of global biodiversity pattern,the formation and maintenance mechanism of ecosystem.Chinese fir plantations was the most common type of artificial vegetation in southern China,which was of great significance in providing forest products and improving ecosystem health.At present,most of the studies on the influencing factors of community dynamic succession and mortality of Chinese fir plantations used the method of space instead of time,and the conclusions were not consistent.How did the community dynamics of Chinese fir plantations change?What were the influencing factors of community death and recruitment in Chinese fir plantations?The mechanism leading to the survival and death of trees in Chinese fir plantations was not clear.Three datasets in 2009,2014 and 2019 from three 1 hm~2 Chinese fir plantations in Gutianshan(GTS)were used to analyze the dynamics of Chinese fir plantations and the relative contribution of topographic and biotic factors on the mortality and recruitment rate of community were discussed.This study was helpful to understand the dynamic law of natural succession of Chinese fir plantations,understand the influencing factors and relative contribution of death and recruitment of Chinese fir plantations,and provided a theoretical basis for sustainable development and vegetation restoration of plantation.The main results were as follows:(1)This study analyzed the dynamic of species composition,important value,species diversity and size class distribution of Chinese fir plantations from 2009 to 2019.The number of species in the three surveys were 120,125,132.10 species decreased and 22 species increased,but the number of plants increased at first and then decreased;The dominant families and dominant species in the community remained basically unchanged,but the important value and its sequence changed greatly.the important value of Cunninghamia lanceolata decreased,and the important value of evergreen tree species increased.The four diversity indexes in the community showed an upward trend,in which Simpson index and Shannon-Wiener index increased significantly,the community size class structure showed multi-peak type,belonging to intermittent development type,the size class of Cunninghamia lanceolata was still in a stable type,while the size class of evergreenbroad-leaved species such as Schima superba showed an increasing type.(2)This study analyzed the death individual distribution,recruitment individual distribution,mortality rate,recruitment rate and population change rate of Chinese fir plantations in 2009-2019.There were no significant change in death,species and plant number of Chinese fir plantations in GTS,but plant death and recruitment showed great differences among different species and size classes.Among them,in the size class,the number of death and complement decreased with the increase of the size class.The mortality and recruitment rate were the highest in 1-5 cm size class.From 2009 to 2019,the population growth rate of 5-15cm size class was negative,but it increases rapidly after 15cm,and reaches the maximum at≥20cm size class..(3)This study discussed the effects of topographic and biotic factors on the death and recruitment of Chinese fir plantations from 2009 to 2019.According to the PCA analysis of environmental factors,the interpretation proportion of the first four axes reached 85.4%,which were 37.5%,22.8%,15.5%and 9.6%,respectively.Mean DBH,Pielou index,Simpson index,plant density,basal area,Shannon-Wienner index,slope,average altitude and aspect were the main influencing factors.Stepwise multiple regression showed that the mortality rate of community was mainly affected by average altitude,basal area,mean DBH,Shannon-Wiener index and Pielou index(P<0.001).Community mortality was negatively correlated with basal area and Pielou index.The community recruitment rate of Chinese fir plantations was negatively correlated with average altitude,plant density,mean DBH and Simpson index,and positively correlated with basal area and Shannon-Wiener index.(P<0.001).(4)This study analyzed the relative importance of topographic factors and biotic factors to community mortality and recruitment.Variation partitioning shows that topographic factors independently explain 3%of the community mortality,biotic factors explained 17%,topographic and biotic factors explained 14%.Topographic factors alone explained 2%of the community recruitment rate,and biotic factors independently explained 16%.Topographic and biological factors together explained 3%.The influence of biotic factors on the community dynamics of Chinese fir plantations in GTS is greater than that of topographic factors.To sum up,the number of species of Chinese fir plantations in GTS increase significantly in the past 10 years.The dominant families and species remain basically unchanged.Chinese fir plantations belongs to intermittent development type.The death and recruitment of the community are similar in the two periods,but there are great differences in different size classes.Topographic factors and biotic factors can affect the death and replenishment of the community,among which biotic factors have a higher explanation rate.Therefore,in this study,the regeneration of Chinese fir plantations in GTS is better,and the community is slowly succession in the direction of evergreen broad-leaved forest.Due to the slow natural succession of Chinese fir plantations,longer-term dynamic monitoring can be carried out in the study of influencing factors,and comprehensive analysis can be carried out at different scales combined with climate change,soil factors and seedling distribution.