Study On The Population Ecological Characteristics Of Abies Georgei Var. Smithii In The Tibet Plateau

Abies georgei var.smithii natural populations taken as the research object,their habitat conditions,community characteristics,age structure,regeneration,transpiration water consumption and physiological plasticity,etc.,were studied systematically basing on the typical plots,lab analysis and the site supervision at the east slope of Sejila Mountain,Southeastern Tibet,China.Meanwhile,the response mechnism and the influencing factors of populations with altitude increaseing were analyzed in order to determined the optimum settlement of A.georgei var.smithii populations.According to the above,the scientific theory should be provided to protect A.georgei var.smithii natural populations.The main results were as follows:?1?A.georgei var.smithii populations mainly distributed in the 3700 4380 m altitude at the study area,where-0.27^-4.52?of the annual average temperature,1237¹340mm of the annual precipitation,and 907²327 h of the average sunshine hours were the special climate characteristics.Brown forest soil was acidic,with the high contents of water and organic matter.Seedlings of A.georgei var.smithii populations had the differently growing preference with the altitude increasing.Such as,they had the fastest high growth at3700 and 3900 m with the most leaves number and total leaf area of them at 4100 m altitude,while the increasing of their basal diameter and root biomass was quick at 4380 m altitude.A.georgei var.smithii populations regeneration only depended on their seed propagation,and unstable yielding in fruiting characteristics was existed.172 plant species,including 121 genera,47 families,were found,81.82% of which belongs to east Asia and Chinese endemic genera among A.georgei var.smithii community.In particular,Asteraceae,Rosaceae and Ericaceae were dominant.Stand density,the quantity of seedlings and saplings showed the decreasing trend with the altitude increasing.The values of biodiversity indexes were low,but that of evenness index(J_sw and E_a)was high.Cutting,grazing,and artificial excavation were the main factoes threating individuals survival.?2?A.georgei var.smithii individuals were random distribution in Sejila Mountain by the method of point pattern analysis.Age structure of A.georgei var.smithii populations showed “L” shape,and their survival curves basically belonged to be Deevey-?,namely a developing population.The mortality was higher on the ?^? age class of seedlings,but lethal factor were different at various elevations.Specific reasons wre as follows:self-thinning rule of populations under the lower altitude,and thick layer of litter or moss preventing the nutrient acquisition though root under the middle altitude,and lower temperature under the higher altitude.On the whole,the quantity of A.georgei var.smithii populations reduced with the age increasing as a similar sine waves with the period of almost60 years.Through the time series prediction,the quantity of A.georgei var.smithii populations less than?age class would reduce after 60,90,and 120 years,and this portended populations would be a decline tendency in the future.At the same time,the ageing populations and their limited distribution were the vital factors leading the population decline.?3?Through the fruiting characteristics of A.georgei var.smithii populations,unstable yielding phenomenon in fruiting was showed with a cycle of 3 years.Plants about ten ages began to fruit,and then reached the full fruit period from 30 to 100 years age.The highest fruit yield per plant appeared at the 3900 m altitude,while the maximum values of density and proportion of fruit-bearing plants appeared at 4300 and 4380 m altitude,respectively.The cone of A.georgei var.smithii mainly inserted in the overstory and the south direction,some indexes of which decreased with the altitude increasing,such as length,width,seed number of single cone,length and width of seed,and 1000 seed weight.The germination rate,germination index and germination potential of seeds ranked in the decreasing order of 20?,25 ?,15 ? and 10 ?,while seeds germination rate was significantly affected by air temperature at the same altitude by one-way anova analysis.?4?Seed rain of A.georgei var.smithii populations started at September,peaked at November or December,and ended at March and May of next year.Density?175 Ind./m²?and the complete seeds proportion?71.25%?of seed rain had the maximum values at 3900 m altitude.On the contrary,both mimum values?60 Ind./m² and 41.43%,respectively?appeared at 4380 m altitude.The very significant positive correlation between density of seed rain and the complete seed proportion existed,with the significant positive correlation between density of seed rain and stand density,species richness.Soil seed bank had the maximum density?206Ind./m²?and the complete seed proportion?38.35%?at 3900 m altitude,with their minmun values?67 Ind./m² and 23.88%,respectively?at 4380 m.More than 70% seed of soil seed bank accumulated the surface to 2 cm depth of soil.Correlation analysis showed that the very significant positive correlation between density of seed soil bank and soil water content existed,with the significant positive correlation between density of seed soil bank and the complete seed proportion,the thickness of litter or moss.Meanwhile,the significant negative correlation between density of seed soil bank and the slope of plots existed.Less than 4 years seedlings accounted for the majority,while more than 5 years were scarce.In genernal,intense spatial aggregation of seedlings was observed at different altitude.Analysis on 10 ecological factors showed climate condition and intensity of disturbance,stand status,and soilcondition had important effects on seedlings survival.?5?By the X² test,interspecific relationships of arbor species showed no significant positive correlation,and which of shrub and herb dominant species were significant positive correlation.However,the association degrees of the species pairs were loose for the JI values in general.A.georgei var.smithii showed random distribution genernally,except the small DBH individuals aggregated distribution.Sorbus rehderiana was aggregated distribution,while Picea likiangensis var.linzhiensis and Sabina saltuaria were random distribution.?6?Sap flow velocity of A.georgei var.smithii individuals and mainly environment factors were monitored at 3850 and 4300 m altitude.For the same characteristics,the monopeak curves of sap flow velocity were observed in summer,but they were weak in winter.The different ones were as follows: the sap flow velocity and duration were the higher and longer at 3850 m than those of 4300 m,and the peak of sap flow was from May to October at 3850 m and from June to September at 4300 m.The the mainly influencing factors of sap flow velocity ranked in the decreasing order of photosynthetically active radiation?PAR?,air temperature?T_a?,rainfall?R_a?,vapor pressure deficit?VPD?and soil water content(S_wc)at 3850 m,with T_a,PAR,R_a,S_wc and air relative humidity in 4300 m altitude.?7?Leaves functional traits and inclusion of A.georgei var.smithii populations were different along the altitude increasing.Leaf area decreasd from 3700 to 4380 m altitude,with specific leaf weight and thickness,antioxidative enzymes activites?superoxide dismutase and ascorbic acid oxidase?and lipid peroxidation?malondialdehyde?content increasing.The maximum values of chlorophyll a,chlorophyll b,carotenoid,nitrogen content and net photosynthetic rate of leaves were observed at 4100 m altitude.The highest light saturation point appeared at 3700 m,while the highest light compensation point and dark respiration rate did at 4380 m.Based on above five groups of indexes,physiological plasticity indexes were calculated,and they ranked in the decreasing order of photosynthetic parameter,enzyme activites and malondialdehyde content,nitrogen content,photosynthetic pigment content,leaf morphologic properties.Accordingly,the suitable distribution area of A.georgei var.smithii populations were determined as the 4100 m altitude in Sejila Mountain.?8?Whith reducing harmful interferences,appropriate human intervention should be taken,such as shrub,grass and moss removed partly,for improving the habitat for A.georgei var.smithii populations regeneration.Based on the above,seed germination rats and seedlings growth should be strengthed to achieve the natural regeneration,the sustainable development and stable survival of A.georgei var.smithii populations.