Study On The Community Characteristics Of Endangered Species Thuja Koraiensis Nakai

Thuja koraiensis Nakai,is an evergreen tree and national second-level key protected plant.It is both an critically endangered species and precious ornamental value and important economic tree.T.koraiensis is mainly distributed in the Changbai Mountain forest area of Jilin Province,with narrow slopes such as hillside valleys at an altitude of 1000-2000 m.In recent years,the T.koraiensis had been disrupted by various human factors,and its habitat has been destroyed.The population size,distribution and individual numbers has been decreasing.It is of great academic value to study its endangered bioecological basis.Based on the typical plot method,this paper carried out an ecological survey of the T.koraiensis community in Changbai Mountain,and used ecological analysis methods,explored the community species composition,flora composition,community structure,niche,interspecific association,and regeneration status,and the results are as follows:(1)There were vascular plant with 43 families of 76 genera and 104 species in T.koraiensis community.11 families such as Compositae,Rosaceae and Liliaceae etc.were dominant families in species.The rate of mono families and mono genera was high,which reflected the antiquity of the plant community.There were 92 species of seed plants belonging to 68 genera and 35 families in T.koraiensis community.The geographic types of the flora was various and predominant with temperate type.To the extent of affecting of the characteristic of T.koraiensis community,North Temperate was of mainly influence,Cosmopolitan and E.Asia & N.Amer.Disjuncted were of great influence.(2)The vertical structure of the community was divided into three layers including tree layer,shrub layer and herb layer.There were 1906 individuals of T.koraiensis,including 1778 in the shrub layer and 128 in the tree layer,which was 43.28% and 3.12% of woody plants in the whole community.The age structure of various populations of T.koraiensis community had 5types including unimodal type,sporadic type,pyramid type,inverse-J type and unibar type.The age structure chart of the T.koraiensis was pyramid type and growth trend was a growing type.The first diameter(DBH < 3 cm)of T.koraiensis had the largest number of plants(1822 plants)and lower mortality rate(2.62%),the 2nd to 5th diameter(3cm?DBH <15)and the 6th to 12 th diameter(DBH?15cm)were relatively small in number of 72 and 12 plants,respectively,but the average mortality rate was as high as 46.27% and 40.00%.In different plots,the vertical structure and age structure of T.koraiensis population had faults.(3)There were 1906 T.koraiensis in the survey plot,only 6 fruit trees were found,the average seed density of the soil seed bank was 102 seeds per square meter,and seeds were no vitality and seedless transformation into seedlings.The natural renewal method of T.koraiensis population was germination regeneration,the population renewal density in the protected area(5350 ~ 11325 plants per hectare)was more than that outside the protected area(1575 ~ 4900 plants per hectare).The height growth of seedlings and young trees showed a fast-slow-fast rhythm,and the speed of growth was slow on the whole,the plant height of 25-year-old T.koraiensis was about 1.2m.(4)The species diversity index and evenness index of the community were low,the community was in an unstable state.The Simpson and Shannon-Wiener indices of community species diversity from small to large were: shrub layer(0.6308,1.4601)<tree layer(0.7139,1.6352)<herb layer(0.7288,1.8407);Peliou indices from small to large was shrub layer(0.5952)<herb layer(0.6840)<tree layer(0.7313).(5)Among the 15 principal tree species of the community,T.koraiensis population ranked third in importance value of 18.39%,however,the horizontal niche width(8.1270)and vertical niche width(2.0962)were smaller,ranking only 7th and 10 th.The lower ranking and narrower niche width reflect that T.koraiensis population has a weak ability to adapt to the environment and apply environmental resources.(6)Among the 15 principal tree species of the community,the horizontal niche overlap was lower,and the vertical niche overlap was higher,reflecting that each principal tree species had obvious differentiation in resource utilization at the horizontal level,and a large degree of similarity to the high resource utilization in the vertical,which mainly consists of light resources.T.koraiensis had little horizontal overlapping with other principal tree species,did not overlap with Prusus maackii,Larix olgensis,Euonymus pauciflorus and Pinus koraiensis,and partially overlapped with the other 10 principal tree species,which showed the different demands forhorizontal resources.The vertical niche overlap between T.koraiensis and other 14 principal tree species was higher,among which it was highly overlapped with Prunus maackii,Abies nephrolepis,and Betula ermanii,and largely overlapped with 8 tree species such as Betula platyphylla,Picea microsperma,and Acer ukurunduense etc.This would lead to more intense competition for resources.(7)The dominant interspecific and interspecific association of the principal tree species of T.koraiensis community were weak,the positive-negative association ratio(0.69)was small,and the community was in an unstable stage.Among the principal tree species,4 pairs were significantly linked,and T.koraiensis and other principal tree species were not significantly linked.16 pairs showed significantly covariance,but T.koraiensis and Viburnum koreanum were significantly positively covariance,T.koraiensis and Prunus maackii and Berula platyphylla showed significantly negative covariance.In summary,the T.koraiensis community was rich in species composition,and the seed plant flora was mainly distributed in the north temperate type.The vertical stratification of the community was obvious.The development trend of the T.koraiensis population was growth type.The number of fruiting tree was very few,there was no seedling,and it was renewed in the form of root and sprouting,but the plant grew very slowly.The T.koraiensis was weak in adapting to habitats and had weak correlation with other principal tree species.