| Zhejiang Gutianshan National Nature Reserve belongs to the subtropical monsoon climate zone.There is a well-preserved evergreen broad-leaved forest vegetation dominated by Castanopsis eyrei and Schima superba in the area,which has important protection and research value.The composition and structure of the evergreen broadleaved forest in Gutianshan were greatly affected by the snow disaster,which was happened in southern China in 2008,but there is not much further research on the longterm and irreversible effects of this impact.Therefore,this study took the 5 ha sample plot in Gutianshan as an example to explore the impact of the 2008 snow disaster on the subsequent community restoration process and the relationship between the subsequent dynamic changes of the community and environmental factors,aiming to provide a theoretical basis for the post-disaster restoration of forest communities.This study was based on two survey data in 2012 and 2017 of the 5 ha forest dynamic monitoring plot established in Gutianshan National Nature Reserve.This study systematically analyzed and discussed the sample plot’s dynamic changes of community structure characteristics such as species composition,important values,growth types,community structure characteristics,diameter class structure,etc.On this basis,the relationship between abiotic factors such as slope and altitude,as well as biological factors such as species richness and plant density,and community dynamics was analyzed,and the impact and driving factors of snow and ice disasters on the community were further analyzed.The results showed that:(1)In 2012,there were 17,398 woody plants with DBH≥1 cm in the plot,belonging to 52 families,108 genera and 158 species;In 2017,there were 16,401 woody plants with DBH≥1 cm in the plot,belonging to 53 families,108 genera and 158 species.The dominant species are Castanopsis eyrei,Chimonanthus salicifolius,et al.In the past 5 years,3 new species have been added and 3 species have disappeared.The newly added and disappeared species were all rare species,and the ranking of the important values of rare species varied greatly.Overall,a total of 145 species had changed their importance values in 5 years,of which 60 species had decreased in the order of importance and 85 had increased in order of importance.The species composition of the plant community was generally stable,and the snow disaster impact of the dominant groups was lower than the overall level of the community.The rare species were greatly affected,and the changes were obvious and irreversible.(2)Species diversity indexes of different growth-type species in the community varied.There were significant changes in the diversity index of shrubs and shrubs or small trees.Shannon-Wiener index and Simpson index of shrubs community decreased(P<0.05),the Pielou index of shrub or small tree communities rose(P<0.1),that was,the diversity of different growth types varied significantly,this phenomenon was mainly related to the formation and development of forest gaps after snow disasters.There were significant differences in the number of individuals and breast area in the plot: the number of individuals in the community decreased significantly,and the area at breast height increased significantly.The study of interspecific relationships found that there was no significant change in species abundance,area at breast height,frequency and order of importance values in 5 years.To some extent,this reflected the stability of the interspecific dominance relationship over the 5 years,that was,the dynamic change direction of forest community was constant in a stable environment after extreme disturbance.(3)The dynamic change of community diameter class structure in the sample plot was studied.The survey results showed that with the diameter class increased,the number of individuals showed a decreasing trend,and the diameter class-individual number diagram showed an inverted "J" structure.The overall structure has not changed significantly,the community plants are still dominated by small diameter plants.Statistical analysis of the number of recruitment,upgrades and dead individuals of different diameter classes showed that the recruitment rate of most diameter classes was greater than the mortality rate,while the mortality rate of individuals of small diameter classes was similar to the recruitment rate,and the number of individuals decreased significantly.The number of individuals and area at breast height of each diameter class in 5 years were analyzed,and the results showed that there were significant changes in the area at breast height and number of individuals in the community of small diameter classes.In general,the dynamic changes of individuals at the trail level affected the overall dynamic changes of the community.The community was in a good state of renewal.The growth type of the post-disaster community was recovering towards the pre-disaster state,and some of the effects of the disaster were gradually offset.(4)This study explored the effects of environmental factors on the mortality,recruitment,and the area at breast height rate in evergreen broad-leaved forests from2012 to 2017.Through stepwise regression,it was found that plant density,average diameter at breast height,average altitude,Shannon-Wiener index,interspecific competition index,species richness,slope,and Pielou index were the main influencing factors.The results showed that: Community mortality was mainly affected by the mean diameter at breast height,mean altitude,Shannon-Wiener index,interspecific competition index,species richness,slope,and Pielou index,among which species richness,Pielou index,and slope were positively correlated with mortality(P < 0.05);community recruitment rate was mainly affected by plant density,average diameter at breast height,species richness,slope,and Shannon-Wiener index,among which slope,Shannon-Wiener index were positively correlated with recruitment rate(P < 0.05);the breast area rate was mainly affected by plant density,species richness,Pielou index,average diameter at breast height,slope,and Shannon-Wiener index,which were negatively correlated with average diameter at breast height,slope,and ShannonWiener index(P = 0.1054).Topographic factors such as slope and altitude had a huge impact on community structure when disasters occur,and also affected community development in the subsequent recovery process.Biological factors such as species richness and community competition affected community dynamics in the subsequent recovery process.(5)In this study,the effects of environmental factors on the mortality and recruitment rates of evergreen broad-leaved forests from 2012 to 2017 were investigated by diameter class.Stepwise regression analysis results showed: In the two diameter ranges of 1-5 cm and 5-10 cm,the model interpretation rate was higher.The individual mortality of 1-5 cm diameter plants was negatively correlated with species richness,and positively correlated with Shannon-Wiener index and interspecific competition index(P <0.05);recruitment rate was correlated with plant density,average diameter at breast height,and species richness and positively correlated with slope and Shannon-Wiener index(P <0.05).The individual mortality rate of 5-10 cm diameter plants was negatively correlated with average DBH,convex,Shannon-Wiener index and interspecific competition index,and was positively correlated with plant density,species richness,slope,aspect,Simpson index and the intraspecific competition index(P <0.05);the individual recruitment rate was negatively correlated with the average DBH,slope,Shannon-Wiener index and intraspecific competition index,and was positively correlated with species richness and Pielou index(P <0.05).The 1-5 cm diameter class population was mainly affected by biological factors such as competition during the recovery process,while the 5-10 cm diameter class population was also affected by topographic factors such as slope aspect.In summary,the community composition of the evergreen broad-leaved forest in Gutianshan was stable from 2012 to 2017,the dominant species remained basically unchanged,the diameter class structure of the community was an inverted "J" type,and the overall renewal status of the community was good.The mortality and recruitment rate of small-diameter plants were high,and the competition for community resources was fierce.Research on impact factors shows that both biotic and abiotic factors affected plant survival.Among them,slope,altitude,etc.were the main abiotic factors,and species richness,plant density and average diameter at breast height,etc.were the main biological factors.The results of this study showed that the evergreen broadleaved forest in Gutianshan was well regenerated,the interspecific relationship was stable,the influencing factors of different diameter-level communities were different,and the small-diameter-level community resources competed fiercely.Subsequent research could be combined with soil factors,climate(light resources,temperature difference,etc.)for further discussion. |
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