The Response Mechanism Of Vegetation Communities To Soil Moisture Changes

Desert riparian forest was studied in the upper, middle and lower reaches of Tarim River. The objectiveof this study was to illuminate the population structure and quantitative dynamic, living status anddevelopment trend in the future. The results of this study were as follows:(1) Proceeded principal component analysis of diversity index and the indexes of soil physical andchemical properties in the studied area of19samples, and screened to more accurately represent the indexof the overall characteristics, then clustered analysis on the basis of all kinds of landlord component indexof19samples was divided into three habitats, The community types of three habitats on the important value(more than10) were: Popuhis euphratica+Tamarix ramosisslma+Phragmites australis+Glycyrrhizainflate、 Popuhis euphratica+Tamarix ramosisslma+Karelinia caspici、 Popuhis euphratica+Tamarixramosisslma+Halogeton glomeratus。the corresponding average soil moisture content were15.05%,16.44%,3.97%.(2) The species was different between different height levels, it belong to the steady state from thethree high level, the only survival was Popuhis euphratica. The diameter classes distributed uniform ofP.euphratica populations in habitat Ⅰ, it belonged to the stable population;The planted and young treeswere numerous in habitat Ⅱ, the number of P.euphratica populations reduced gradually with the increaseof age class, the overall performance was the growing population. The quantity of each age level forP.euphratica populations were lower than other habitats in habitat Ⅲ, the seedlings of rank Ⅰ was lackseriously, so it belonged to the recession population in the habitat condition.(3) P.euphratica, Tamarix ramosisslma, Glycyrrhiza inflate had the aggregate distribution in five spacescales, only the Hcdimodendron halodendron was the random distribution in15m×15m. Tamarixramosisslma and Hcdimodendron halodendron in the shrub layer, Glycyrrhiza inflate of herb layer weremeasured by C、m2、I、Ｉδ,the index were greater than P.euphratica populations of tree layer,the threepopulations had higher concentration than P.euphratica populations.(4) The niche breadth of dominant species—P.euphratica is biggest in three habitats, showedthemaximum using of resources and competitive ability.The niche breadth of P.euphratica and Tamarixramosisslma decreased obviously in habitat Ⅲ.The species pairs scale of0.1-0.2range was the most inhabitat Ⅰ and Ⅲ. The niche breadth was concentrated in the0.10to0.50in habitat Ⅱ, it l accounted for80%of the total species pairs.Most of the desert riparian vegetation species could only occupy a smallerniche breadth, they were in accompanying species or occasional species status.(5)The species pairs of P.euphratica overlap and other species were0.60,they accounted for60.70%ofthe total in habitat Ⅰ. Theniche overlap value was1.00of Tamarix ramosisslma and SophomalopccuroidcsL., Glycyrrhiza inflate and Eragrostis pilosa,0.99of Tamarix ramosisslma and Lyciumruthenicum in habitat Ⅱ. Theoverlap index is higher of Phragmites australis, Hexinia polydichotoma,Haloaicrmum strobiiaceum and other species in habitat Ⅲ. The species pairs of0-0.1range is the most inthree habitats,0.8to1.00took the second place, and the niche overlap ratio of the two interval accountedrespectively for88.18%,51.05%,69.70%of the total. The overlap ratio of0.1-0.8rangewas low generally.(6) We should first restore the adaptable species like the native species-P.euphratica, Tamarixramosisslma as pioneer species in the vegetation restoration and management of the tarim river middlereaches, bild the community of dominant population on these species to restore desert riparian forest, andthen through the community succession to form stable ecological system type, achieved gradually the goalof vegetation restoration.