| There is a complete mixed evergreen deciduous broad-leaved forest in the Jin Zi Mountain Forest farm,which is of great conservation significance and research value.To study the dynamic changes of the mixed green deciduous broad-leaved forest in the forest farm can further understand the law of community dynamic changes and development,so as to provide certain data support and theoretical basis for forest sustainable management in the region in the future.Based on the survey data of the 6hm~2fixed monitoring plot of Jin Zi Mountain State-owned forest Farm in 2016 and2021,this study analyzed the community species diversity,its composition changes,the overall distribution characteristics and spatial distribution patterns of dead and replacement individuals in the sample plot of evergreen deciduous broad-leaved mixed forest,and explored the environmental factors affecting the dynamics of community death and replacement.The main results are as follows:1.There was little change in community species diversity and composition during 2016-2021,and the community structure was relatively stable.During the five years,the total number of woody plants decreased obviously,but the number of families and genera did not change,the number of species increased slightly,and the newly added and disappeared species were rare species.With the exception of the species richness index,all diversity indexes decreased slightly compared with 2016.Except for three species whose importance value is more than or equal to 1,the importance value and its ranking of other species have changed to some extent,and the importance value fluctuates within 1,while the dominant families and species of the community remain basically unchanged.The average DBH of all species in the plot was small and showed an increasing trend.The individual diameter class structure of all species in the plot showed an inverted“J”shape distribution during the two surveys,and there was no significant difference between the overall diameter class structure of all species and the diameter class structure of dominant species.2.The community had strong natural regeneration ability,and the community was in a state of forward succession.A total of 5924 dead individuals were found in the second survey in 2021,belonging to 49 families,88 genera and 131 species,with an average DBH of 2.38 cm.There were 3616 new individuals,belonging to 43families,67 genera and 102 species,with a mean DBH of 1.61 cm.The average annual mortality rate of all species in the sample plot is 4.76%,and the average annual replacement rate is 2.89%.The population variation rate of the dominant species Carpinus fargesiana(6.57%)was significantly higher than that of other populations.The mortality and replacement rate of diameter classⅠ(1～5 cm)were the highest,and the number of deaths and replacement decreased rapidly with the increase of diameter class.The diameter class structure of all dead individuals showed an inverted“J”shape distribution,and the diameter class structure of dead individuals of each dominant species was basically consistent with that of dominant species of living trees in the first survey in this plot.All the replacement individuals were small diameter,and each dominant species had replacement individuals.3.The spatial distribution of the dead and regenerated individuals of the dominant species in this sample plot is consistent with that of the dominant species in2016,and its spatial distribution pattern has not been destroyed,indicating that the stability of the community is remarkable.The spatial distribution of dead and regenerating individuals of different dominant species in the plot showed certain similarity and complementarity.All dead individuals were randomly distributed at 44～45 m scale,and aggregated at other scales.The aggregation of dead individuals of dominant species decreased with the increase of sampling scale.All the replacement individuals showed aggregation distribution at the scale of 0～50 m,and the replacement individuals also showed the characteristics of decreasing aggregation degree with the increase of sampling scale.4 Stepwise regression analysis showed that the community mortality was mainly affected by Simpson index,chest height area and Shannon-Wiener index.The replacement rate was mainly affected by Pielou index,plant density and mean DBH.At different diameter levels,the effects of various factors on death and replacement rate were different.The death and replacement of individuals in small diameter classes(1～10 cm)are mainly affected by plant density,Pielou index,chest height area,average breast diameter and Simpson index.In contrast,the death and replacement of middle diameter class(10～20 cm)individuals were also affected by mean altitude and species richness,while the death and replacement of large diameter class(DBH≥20 cm)individuals were mainly affected by mean DBH and chest height area.In addition,variance decomposition analysis showed that the explanatory rates of topographic factors to the overall mortality and replacement rate of the community in the sample plot were 3.02%and 2.59%,respectively,and the explanatory rates of biological factors to the overall mortality and replacement rate of the community were17.25%and 9.02%,respectively.Generally speaking,the explanation rate of topography to mortality and replacement rate is generally lower than that of biological factors.To sum up,during 2016-2021,the number of plants decreased,the number of species increased,and the dominant species remained basically unchanged.The overall diameter class structure was inverted“J”type,and the community replacement was good as a whole.Small-diameter individual plants have the highest proportion of death and replacement,and the competition for community resources is fierce.All environmental factors jointly affected community death and replacement,and the effects of environmental factors on different diameter classes were different,but overall biological factors had a better explanation rate for community death and replacement. |
