| Cercidiphyllum japonicum a relic species of paleotropical kingdom in Tertiary period,is listed as a key second-class protective plant in China.For a long time,because of its physiological characteristics and human activities,its natural distribution in the wild becomes rare,and it is on the verge of extinction.This essay studied on the population dynamics of C japonicum in Heizhugou National Nature Reserve of Sichuan Province,based on field investigation,digital herbarium,and distribution data of C japonicum in related literature,combined with the climate factors,soil factors and geomorphic factors related to the growth of C japonicum,used MaxEnt method and GIS to measure the potential suitable distribution areas of C japonicum in Sichuan Province,divided the suitable areas accordingly,and analyzed the related factors affecting the growth and distribution of the C japonicum.The main results are as follows:(1)The study on the population dynamics of C japonicum in Heizhugou nature reserve shows that:the diameter class structure of C japonicum group is spinning cone type,there are a good number of middle-sized plants,less number of saplings and old individuals,which indicates the declining population and tendency;the population is seriously short of saplings,and the highest death rate of the population goes to the Ⅷ diameter class,i.e.,the population is closer to the average physiological life when approaching the Ⅷ diameter class;the survival curve of C japonicum appears convex type curve,which belongs to Deevey Ⅰ curve and recession trend;the death rate of population fluctuates in waves,both the mortality rate and deficiency ratio show the rise-fall-rise-fall-rise tendency;the quantitative analysis of population dynamics illustrates that the population dynamics show the phenomenon of alternative growth and decline,albeit the overall performance is reducing,the prediction results of time series show that in the next 2,4,6,8 years,the number of saplings and middle-sized individuals decreases with the passage of time,and the number of old individuals increases,showing a declining trend.The main reason for the decline of this population is the severe shortage of young seedlings.(2)The AUC curve generated automatically based on MaxEnt method shows:the AUC value of the prediction result is 0.987,which indicates that the prediction result has high credibility.There are 15 environmental variables affecting the distribution of C japonicum,including 9 climatic factors,4 soil factors and 2 terrain factors.Among them,the lowest temperature tmin06(48.5%),the average precipitation prec03(23.1%),the soil available water capacity(14.1%),the average precipitation bio19(4.9%),the average solar radiation srad06(3.2%),the soil subclass(3.1%),the slope direction(1.1%),the coldest and lowest temperature bio06(0.7%)and the highest temperature bio05(0.5%)in the hottest month,soil clay content(0.2%),slope(0.2%),average temperature in the driest quarter(bio 9)(0.1%),monthly mean temperature difference between day and night(bio 02)(0.1%),soil organic carbon(0.1%),and rainfall in the driest month(bio 14)(0.1%)are ranging from the top according to the contribution rate.(3)Through the analysis of the response curve of 15 environmental factors,the suitable ecological environment of the C japonicum is obtained:①climate and environmental variables:the suitable range of the driest month rainfall is 2.5-28mm,the average rainfall in the coldest quarter is 32mm,the suitable range of the monthly mean distribution of diurnal temperature difference is 8.7-12.2℃,the highest temperature in the hottest month is 23℃,the lowest temperature in the coldest month is-2℃,the optimum temperature in the driest season is 0℃,the average precipitation in March is 48mm,and the average solar radiation in June is 14800 KJ·m-2·d-1,and the most suitable temperature for the growth and distribution of C japonicum goes to the lowest temperature in June of 14℃;②the soil types suitable for the C japonicum distribution are cinnamon soil,yellow brown soil,brown calcium soil,soil clay content of 22.5%,soil available water capacity of 1[100(mm/M)],soil organic carbon content of 3%,which is the most suitable for the growth of C japonicum,③geomorphic variables:the most suitable area for the growth and distribution of C japonicum occurs at the region with northwest slope and aspect 43-45°.(4)The range of longitude&latitude of the potential suitable area for Sichuan C japonicum is 28°N-34°N,102°E-105E.In terms of landform,it is mainly located in the edge zone near Sichuan basin,started from the basin to Western Sichuan Plateau,Minshan,Longmen Mountain,Jiuding Mountain,Qionglai mountain,Emei Mountain and Daliang Mountain.This area is mainly concentrated in the northeast and southeast sporadic spots of Aba Tibetan Autonomous Prefecture(Jiuzhaigou County,Songpan County,Wenchuan County,Maoxian County,Lixian County),the north of Mianyang and the central and western regions(Pingwu County,Beichuan Qiang Autonomous County),Deyang and the northwest of Chengdu(Mianzhu City,Dujiangyan City),most of Ya’an(Baoxing County,Tianquan County Hanyuan County,Shimian County,the west of Meishan City(Hongya County),the west of Leshan City(Emeishan City,Ebian County,Mabian county),the northeast of Liangshan Yi Autonomous Prefecture(Ganluo County,Yuexi County,Meigu County,Leibo County,Yanyuan County);local protection is mainly carried out in the middle and high-level areas,and ex situ conservation is mainly carried out in the low and unsuitable areas,apart from the two measures,it is also necessary to strengthen the artificial propagation funding together with the promotion and education programs of endangered plants. |
PDF Full Text Request