Population Ecological Characteristics And Variation Of Phenotypic Traits Research Of An Extremely Small Population,Michelia Wilsonii

The study of population ecological characteristics and the variation of phenotypic traits based on an extremely small population is of great significance for understanding the survival status and development trends of natural populations,exploring their endangered mechanisms,and putting forward strategies for population restoration and reconstruction.Focus on the wild population of Michelia wilsonii in Zhougong mountain,Ya’an City,investigated the community diversity,analysis of community plant composition,calculated the importance value and community diversity index;according to the theory of space replacement time,compiled the static life table and plotted the survival curve,mortality curve,disappearance rate curve,survival function curve,and the forecasting model of time sequence analysis was used to quantify the population dynamics;the variance/mean ratio method was used to reflected the population spatial distribution pattern,the inner and intra species competition relationship was reflected by competition index model for individual tree;part of the phenotypic characters of leaf,fruit and seed were selected for variation and correlation analysis,we preliminarily discussed the endangered causes of M.wilsonii and put forward the corresponding protection measures.The results showed that:(1)There are 75 species of vascular plants in the community of M.wilsonii,belonging to 42 families and 61 genera.M.wilsonii,Phyllostachys heteroclada and Hypolepis punctate are the species with the highest importance value in the tree layer,shrub layer and herb layer respectively.The species richness and species evenness showed the same trend,which is the shrub layer > tree layer > herb layer.And the α diversity of the three layers of the community is low in general.The M.wilsonii population in Zhougong mountain is still in the primary stage.(2)The age structure dynamic index Vpi ’and Vpi of M.wilsonii population are both greater than 0.The age structure is inverted J-shaped,the survival curve tends to Deevey-Ⅱtype,which showed that the M.wilsonii population was the growing type.However,the development of seedlings to saplings is hindered,and the supplement of saplings to medium and strong trees is also reduced.The results of survival analysis show that the population has the risk of generational decline.The forecasting model of time sequence analysis also shows that after the next 2,4,6 and 8 years of age class,the number of individuals in medium and strong tree stages has a decreasing trend.The population has the characteristics of sharp reduction in the early stage,stable in the middle stage and decline in the late stage.(3)Overall,the spatial distribution pattern of M.wilsonii population in different age classes and different sampling scales is mainly clumped distribution.With the increase of age,the distribution pattern gradually diffuses from the clumped distribution to the random distribution.With the increase of sampling scale,the aggregation degree of the population gradually decreases,showing the trend of outward diffusion.The intraspecific competition of M.wilsonii population is stronger than interspecific competition,small and medium tree stages are the key stage that needs to be protected.In the interspecific competition,the associated tree species with larger diameter will cause stronger competition to M.wilsonii,among them,Cunninghamia lanceolata and Cerasus conradinae are the most competitive species,the resulting competitive index accounts for 11.25% and 4.86% respectively.(4)The phenotypic variation of M.wilsonii is abundant,the average variation coefficient of 21 phenotypic characters is 26.11%.Among the three organs of leaf,fruit and seed,the average variation coefficient of seed characters is the largest,38.10%.The fruit and seed characters of old trees are significantly better than those of middle and strong trees.There are more abortive follicles and seeds on the aggregate fruit with longer longitudinal diameter.The lower hundred seeds weight,the more follicles and seeds are aborted.The follicles near the upper part have a higher abortion rate.(5)In order to protect and expand the wild population of M.wilsonii.It is suggested to remove underbrush,improve the undergrowth transparency,promote the transformation of seedlings to saplings,reduce the intense intraspecific competition.,establish a protection area and reduce the man-made damage.Finally,provide the conditions for natural regeneration of the population.