Study On Desert Vegetation In The Dry Valley Of The Middlestream Lancangjiang River

There is a special vegetation type that has long been ignored in the dry valley ofThree Parallel Rivers District. Except for the arid valley vegetation of midstream ofNujiang River and upper reaches of the Jinshajiang River which studied by ZhuangCui-zhen, Li Yun-qin and some other people, the desert vegetation of dry valley ofLancangjiang River is the only one remained unstudied.With set102plots from Yunling (Deqin of Yunnan) to Quzika (Mangkang of Tibet)along the midstream of Lancangjiang River, the methods of line survey and typical plotsare adopted in this dissertation. By the basic of identifying specimens and reviewingliterature, this dissertation analysed the arid valley vegetation of midstream of theLancangjiang River, including flora, community characteristics (expounded the vegetationtype of this area is arid valley desert, by comparing community appearance, frequencylevel, life form, and species richness), and divided the community patterns further, studiedthe similarities and regular patten among them. Compared with the desert vegetation of themidstream arid valley of Nujiang River in Tibet and northwest Alashan desert vegetation,this dissertation discussed Lancangjiang River arid valley desert vegetation types is exist,for understanding and research southwest arid valley vegetation provide relatedinformation and scientific arguments.The results showed that:(1) Vegetation that located during the range of2100–2800m of the button of the area,are mainly consisted of subshrub and shrub, without tree. The face characters of theCommunity are few, scattered and low, coverage extremely low (usually between3%and25%), and land surface with large area exposure. The annual evaporation is more than8time of precipitation, which is below300mm. Basic characters of desert vegetation isrepealed.(2) Synthesized vegetation and ground matrix, this dissertation classified the subtype of desert vegetation of Lancangjiang River dry valley into4Form., which including7Ass., which are Form. Vitex negundo var. microphylla,(including Subass. Vitex negundovar. microphylla on stone, and Subass. Vitex negundo var. microphylla on Soil), Form.Sophora davidii,(Ass. Sophora davidii), Form. Caryopteris forrestii var.minor-Ceratostigma minus-Indigofera calcicola (Ass. Caryopteris forrestii var. minor, Ass.Ceratostigma minus, Ass. Indigofera calcicola), and Form. Jasminum nudiflorum var.pulvinatum (Ass. Jasminum nudiflorum var. pulvinatum). The elevation range is2100to2800m above sea level, the Coverage of vegetation is between (1)5～25(40)%,(20)40～80(200)cm height.(3) Components of species:115species representing100genus and56families arecollected. As the Compositae (14species,12families), Poaceae (12species,12families)and Papilionaceae (7species,6families) is advantage family. There are78kinds of herbplants,6lianas and32shrub plants. Among them, include ferns (10species,7genera,7 families); dicotyledonous of angiosperms (85species,73genera,43families);monocotyledons (20species,20genera,6families).32species are shrubs,78species areherbs, and6species are vines. The number of quadratic species is between5～24kinds,average about13kinds.(4) Life-forms，leaf type and frequency: the phaenerophytes take up the largest (45species, take39.1%), and the dwarf phanerophytes take second (26species, take22.6%).Leaf type is mainly to micro leaves (take51.3%) and small leaves (take29.6%), The Afrequency of vascular plants has92species, take80.0%, reflecting the local climate isdrought..(5) Flora: from the areal-types of the vascular plants genera of study area, the genus oftropical ingredients apparently dominant slightly (42.0%), while the genus of northerntemperate ingredients in the second place (40.7%), but the number of species of tropicalingredients (39.6%) is slightly less than the number of northern temperate ingredients(42.9%). It reflected that the dry valley river desert vegetation flora of midstream ofLancang River has Tropical Affinities in the evolve process, and has a larger history withnorthern temperate ingredients meantime.There are72species belong to east-asian ingrdients in the areal-types of the vascularplants species, which take80.8%. The extrem high percent of East-Asian shows thatspecies are deeply efected by the keeping deeply embedding of Himalayan valley, andformed to a particular dry community.(6) Altitudinal gradient pattern: The most widely distributed formation is Form Vitexmicrophylla-Leptodermis pilosa var. microphylla in the upper reaches of JinshajiangRiver dry valley, elevation of distribution range is2000～2800meters; shrub speciesrichness and altitudinal gradient changes are significantly positive correlation, Alataloevenness index of biodiversity and the altitudinal gradient changes are negativecorrelation.(7) Based on the Lancangjiang River Yunling to Quzika valley’s Regional Climatefeatures, severity of drought, vegetation characteristics analysis, and combined with thedivision of deseert in “Chinese vegetaion”, it is believed that the vegetation type in thevalley is belonged to the type which is long neglected in our country, and is a newvegetation type which generated from specific habitats azonal, named “arid valley desertvegetation” desert vegetation of dry river valley.