Community Structure And Quantitative Dynamics Of Pinus Armandii-abies Chayuensi Mixed Forest In Chayu County

The structure and quantitative dynamics of forest communities are important research topics in the field of ecology.Combining various influencing factors to analyze the spatial distribution pattern and dynamic changes of species will help to understand the response strategies of populations to disturbances,community construction and succession,and many other ecological issues.Natural mixed forest is the main forest type in Chayu County,Southeast Tibet.In recent years,the research on this area mainly focuses on the structure of single population and species diversity,while the research on natural mixed forest in this area is very little.After on-site ecological investigation,The number of medium to large diameter trees in the natural mixed forest of Chayu County is relatively small,and the crown diameter is generally small,This indicates that there may be some problems with natural regeneration in this community.In order to gain a deeper understanding of the structure and dynamics of local mixed forests,this article takes the Cheyingou Pinus armandii Abies chayuensis mixed forest in Chayu County,southeastern Tibet as the research object.The community was surveyed using typical plot methods,using methods such as diameter class structure,static life table,survival analysis,and point pattern.The aim is to explore the causes of interspecific relationships and spatial distribution patterns of species from the perspective of community structure and quantitative dynamics analysis,Master the growth status of forest communities,explore the ecological relationships between forest communities and the environment and species,and predict the development trend of the population in the future,in order to enrich and improve the functions and structure of the natural mixed forest ecosystem in Chayu County,and provide theoretical support for species protection and sustainable management of natural mixed forests.The main research findings are as follows:(1)The main tree species in the community are 240 Abies chayuensis,222 Pinus armandii,and 97 Betula utilis.There are 13 species of vascular plants in the understory shrubs and herbaceous layers,belonging to 11 families,12 genera,and a total of 3701 plants;The diameter class structure shows that the 1-4diameter class individuals of the Abies chayuensis and Pinus armandii populations account for 78% and 66% of the total number of various groups,respectively.The distribution of the number of Betula utilis is only on the 1-7diameter class,and as the diameter class increases,the number of various groups fluctuates irregularly,with a large number of medium to large diameter class forest trees missing,resulting in an unstable community.(2)Use methods such as static life table,survival curve,survival function analysis,and time series prediction to study the dynamic structure of various tree populations.The survival curves of the populations of Abies chayuensis and Betula utilis are both Deevey-II type,indicating that the mortality rates of the two populations are similar in their respective age groups.The survival curve of the Pinus armandii population is of Deevey-III type,indicating that the high mortality rate of the population occurs in the early stage and is updated to a small number of adult individuals;The analysis of static life table,dynamic index,and survival function indicate that the mortality and disappearance rate curves of the three types of trees show an irregular wave state,and all began to decline from the middle age class.The age class structure is relatively unstable,and the ability to resist external interference is poor;Time series analysis shows that the number of each age class of the three tree populations in the community should show an overall increasing trend in the next 2,4,and 6 age classes.However,considering the current situation in the region,although there are many seedlings in the population,the regeneration potential is insufficient,and the future population will be in a decreasing trend.Time series prediction cannot consider this ecological process.(3)The analysis of spatial distribution pattern is of great significance for understanding community structure and its renewal.Using point pattern analysis,it is found that various small trees in clusters are mainly clustered,while the spatial distribution pattern of large trees is mainly clustered and random;The spatial correlation between big trees and small trees as a whole,and the spatial correlation between various groups of big trees are diversified due to different plots,which are mainly divided into uncorrelated and negatively correlated;The spatial correlation between small trees and shrubs in each tree population is mainly negative at a small scale,and gradually becomes uncorrelated as the scale increases;The overall spatial correlation between the Abies chayuensis,Pinus armandii,and shrubs showed diversity due to differences in sample plots,with two main types of negative correlation and non-correlation.The spatial correlation between the Betula utilis and shrubs showed non-correlation within the studied scale.This indicates that there is asymmetric competition and intense competition between trees and shrubs.