Studies On The Population Ecology Of Lagerstroemia Minuticarpa Under Two Habitats In Motuo Tibet

The Lagerstroemia minuticarpa in Tibet is only distributed in Motuo county,except the block distribution in miri village as an dominant species,it also scattered in other places.In order to explore the dynamics of population,influence mechanism and the future development trend of L.Minuticarpa,this research was conducted by using the adjacent grid method to investigate L.minuticarpa population in the case of severe interference and slight disturbance.Based on the principles of ecology and statistics,the population structure,dynamics,spatial distribution pattern,intraspecific and interspecific competition intensity and seedling regeneration of L.Minuticarpa were analyzed.The main results are as follows:(1)Population structure and dynamic analysis of L.minuticarpa in two habitatsBase on the field survey data of L.minuticarpa population under natural condition in Motuo Tibet,the trees were graded according to the DBH size.The age structure was replaced by the forest diameter structure,the static life table,the curves of survival rate,mortality rate and vanish rate and four survival function curves were drawn,and the population structure and dynamic characteristics of L.minuticarpa were predicted by the adoption of the time sequence model and quantitative method of population dynamics in this paper.Results showed that:In two habitats,the population of L.minuticarpa fit in with the growing type,the number of seedlings in severe disturbance habitat is richer than in lightly disturbed habitat;Vpi and V'pi was greater than zero when take external interference into consideration,but sensitive to the external disturbance.The survival curve tended toward Deevey-? type,which indicated that the mortality rate in different age-classes was similar.The changing trend of the curve of mortality rate is the same as the curve of vanish rate,there are 3 peaks at the same time;Time sequence model suggested that the numbers of medium and big trees will be climbed in the age-classes of 2,4,6,8.(2)The spatial distribution pattern of L.minuticarpa in two habitatsBased on the diffusion coefficient,aggregation index,Cassie index,negative binomial distribution index,mean crowding degree index,patchiness index,the spatial distribution pattern of L.minuticarpa population at different age classes in different sample plots and habitats was analyzed.The results showed that The population of L.minuticarpa in different habitats was clustered,the aggregation intensity of L.minuticarpa in heavily disturbed habitat was universally higher than that in mild disturbance habitat.The seedlings,small trees,and middle trees were clustered in different age classes,and the big trees were randomly distributed.The aggregation intensity of seedlings and small trees in heavily disturbed habitat was greater than that in the lightly disturbed habitat,but the aggregation intensity of the middle tree and big tree is opposite to the seedlings and small trees.In general,the spatial pattern of L.minuticarpa population was clustered,and the aggregation intensity in heavily disturbed habitat was greater than that in lightly disturbed habitat.(3)The intraspecific and interspecific competition of L.minuticarpa population in lightly disturbed habitatThe optimum neighbor competition range of L.minuticarpa population was ensured as 4 meters in lightly disturbed habitat by the adoption of gradually expanding range method.The competition index of target trees was 268.24,the intraspecific competition index was 183.23,the interspecific competition index was 85.01,intraspecific competition intensity is greater than interspecific competition intensity,the competition intensity of different species is as follows:Lagerstroemia minuticarpa>Terminalia myriocarpa>Castanopsis indica>Syzygium xizangense>Ostodes katharinae.When the DBH was greater than 22.5 centimeters,the changes in competitive intensity was not obvious,and with the growth of diameter class of target trees,the average competition index decreased.The competition intensity of target trees was mainly from the competitive trees which intraspecific diameter class was greater than 27.5 centimeters,and the interspecific diamter class was from 12.5 to 17.5 centimeters.With the growth of diameter class of target trees,the average competition index increased.The relationship between competition intensity and DBH of target trees follows the power function distribution.So the model could well predict the competition intensity of target trees and whole forest stand as well as intraspecific competition.(4)seedling regeneration of L.minuticarpa population in two habitatsL.minuticarpa population were investigated in two habitats by using line transect method.The results showed that there were two kinds of seedling regeneration of L.minuticarpa in two habitats,seedling and sprout.The seedlings are rare,mainly due to regeneration on the stump.The numbers of base diameter class of sprout in heavily disturbed habitat was greater than it in lightly disturbed habitat.In two habitats,the numbers of seedlings reached the highest number at the second base level,and the minimum number at the fifth base level.The conversion rate of L.minuticarpa population was all 100.00%in the first,second and fifth,sixth diameter class.The conversion rate at the second and third diameter class in lightly disturbed habitat was obviously greater than that in heavily disturbed habitat,and the conversion rate at the third,fourth and fifth diameter class was slightly greater than that in heavily disturbed habitat.With the increase of the height of seedling,the number of it tended to decrease.The regression model of the base diameter and height of L.minuticarpa is a polynomial function in heavily disturbed habitat,and it fit in with power function in lightly disturbed habitat.Based on the results of this study,the strategies for the conservation of wild germplasm resources of L.minuticarpa were proposed.The first is the protection of original habitat of wild germplasm resources,the second is ex-situ conservation with the combination of ornamental characteristics,the third is the study on the physiology,ecology,reproduction ecology and conservation genetics to reveal the genetic characteristics of L.minuticarpa.Through the protection of L.minuticarpa population,it can lay a theoretical foundation for further research on the application and cultivation of new species of L.minuticarpa in urban landscape.