Study On Spatial Distribution Pattern And Suitability Of The Original Metasequoia Glyptostroboides Population

Metasequoia glyptostroboides is a endemic relict plant in China,belonging to the Cupressaceae Metasequoia,which is a national class I protected tree species,known as "living fossils." It is mainly distributed in the extremely narrow triangle regions of western Hubei(Lichuan,Hubei),east Chongqing(Shizhu,Chongqing)and western Hunan(Longshan,Hunan).At present,the original Metasequoia glyptostroboides population is faced with the problems of natural regeneration and serious disturbance to population individuals and their habitats,the decline of original populations has attracted much attention.In this paper,the original Metasequoia glyptostroboides population distributed in Lichuan,Hubei Province studied,By means of population resources and habitat survey,population structure analysis,point pattern analysis,functional traits and MaxEnt niche model analysis,the spatial distribution pattern and suitability of the original Metasequoia glyptostroboides population were studied,The main conclusions are as follows:(1)The original existing Metasequoia glyptostroboides population has 5 696 trees in total,including 5 663 in Lichuan,Hubei Province,5 in Longshan,Hunan Province,and 28 in Shizhu,Chongqing.The original Metasequoia glyptostroboides population in Lichuan,Hubei Province accounted for 99.4% of the total trees.The age structure and height structure of the original Metasequoia glyptostroboides population were spinning cone type.The population of ?-? grade adult individuals is the largest,while the number of middle-aged and old-aged individuals of ?-? and ?-X is relatively small.The natural regeneration of the population is severely deficient,and it is a declining population.(2)The stand environments of the original Metasequoia glyptostroboides population were generally located at the road edge,mountain stream,field house,hillside forest,etc.The distribution was mainly concentrated in the elevation from1100 m to 1 400 m.Most of them grew at the slope-flat area,and also widely distributed in the east slope and west slope area.According to the population surveyin the region,8.92% of the individuals were found to be in a poor growth state,and were suffering from serious human disturbances and natural disasters,of which 40 individuals were in the verge of deathd state and 465 individuals were in a weak state.(3)Based on the complete spatial randomness model,the original Metasequoia glyptostroboides population were clustered on the whole scale.The medium-aged trees presented as the aggregation distribution at 0-3 300 m scale,the adult trees and the old trees were aggregation distribution at 0-4 700 m scale,and the three age groups were the positive correlation between each other in all scales.The aggregation scale was decreased after excluding the influence of habitat heterogeneity,and the aggregation scale of the whole population and different age levels were 0-3 000 m?0-2 100 m ? 0-2 900 m and 0-2 500 m,respectively,while there was a positive correlation between the different age levels in 0-2 800 m.From the present spatial pattern,the population mainly presented as the clustered distribution,and the positive relationships which promoted each other between each age class were showed,the habitat heterogeneity and diffusion limitation were the main causes of this pattern.(4)Choose leaf area(LA),specific leaf area(SLA),leaf dry matter content(LDMC),leaf carbon content(LCC),leaf nitrogen content(LNC),leaf total phosphorus content(LPC),leaf carbon to nitrogen ratio(LC/N),leaf nitrogen to phosphorus ratio(LN/P)8 leaf character indicators,as well as branch dry matter content(BDMC),branch total carbon content(BCC),branch total nitrogen content(BNC),branch total phosphorus content(BPC),Branch carbon-to-nitrogen ratio(BC/N),branch nitrogen-to-phosphorus ratio(BN/P)six branch trait indicators were used to study the functional traits of Metasequoia native population.Analysis found,There some variations existed at different degrees for14 functional traits of the original Metasequoia glyptostroboides population,and the coefficient of variation varied between 2.9%~63.22%.The variation of LN/P was the largest among them,the coefficient of variation was 63.22%,and the coefficient of variation of LCC and BCC were the smallest,4.5% and 2.9%,respectively,showing the strong internal stability.There were some complex correlations between the traits,which indicated that thefunctional traits of original Metasequoia glyptostroboides population were closely combined,and influenced interact and mutual restraint each other,and forming a series of functional traits combinations finally to adapt the changes of environment.(5)Environmental conditions are the main factors affecting the variation of functional traits of original Metasequoia glyptostroboides populations.Different site and disturbance environmental factors have different effects on the variation of functional traits of original Metasequoia glyptostroboides populations.The 14 functional traits of the original Metasequoia glyptostroboides population were significantly different under different environmental conditions,the altitude had significant influences on LA?LDMC?SLA and BPC(P>0.05),and the large variation were at 1 200-1 400 m and 1 400-1 600 m;The slope had significant effects on LDMC?SLA and BDMC(P>0.05),and significant variations were at 6-15° and ?36 °;Slope direction had significant influences on LA ? SLA ? LNC and LC/N(P>0.05),but the variations were small and stable;The slope position had significant effects on the characteristics of the branches,including BDMC?BNC and BPC;However,there was only significant effect on leaf area in leaf characters.Different disturbance types had significant effects on most functional characters,including LDMC?SLA?LNC?BDMC?BNC?BC/N?BPC and BN/P,and showed large variation under natural and human disturbances.Variation of the original Metasequoia glyptostroboides population in different environments proved that the population adapted to the change of environment by regulating its own functional traits so as to form the best adaptation strategy.(6)The MaxEnt model was used to predict the suitability of the original Metasequoia glyptostroboides population.The model showed that the potential distribution area of this population was concentrated in the northern area of Zhonglu Town,Fubao Mountains and Wangying Town.Water was the limitation factor for the distribution of this population,the precipitation of the most arid month,the precipitation of the most humid season,the precipitation of the most humid month,and the mean temperature of the most humid season were the importantenvironmental factors restricting the distribution pattern of the original Metasequoia glyptostroboides population.and the suitable growth range were 26.5-27.9 mm ?600-611 mm?86-88 mm?194-209?,respectively.Altitude had the greatest influence on its distribution among the topographic factors,and the suitable growth range covered from1 200 m to 1 500 m.The AUC value of the model was 0.966,and the simulation effect reached the optimal level,which proved that the prediction accuracy of the model was high,and the model could better reflect the potential distribution of the original Metasequoia glyptostroboides population in the study area.