The Structure And Dynamics Of Plant Communities And The Dominant Population In Minqin Desert Grassland

Minqin desert grassland is a part of Mongolian-Xinjiang plateau of Chinese grassland region,and lies in the arid desert region of lower reaches of Shiyang River,which is the result of natural succession of long-term adaptation of natural and social environment in specific circumstances.It plays a very important role in maintaining the stability of ecological environment and resisting sand hazard as well as promoting the development of grassland agriculture.So it has the extremely important significance in studying vegetation dynamic changes and characteristics of plant communities for the local eco-environment construction and socio-economic development in the region.Based on major plant communities in Minqin desert grassland,the type of major plant communities, distribution,area,habitat conditions and community characteristics were analyzed through field investigation combined with "GIS" technology methods.The main contents of this study were the type of Minqin desert grassland,plant community types and its distribution,the characteristics of plant communities' structure (including species quantity composition,appearance,diversity,the dominant species populations and distribution pattern,etc.).Through solving age structure curve of the dominant species and a static life curve,the dynamic changes and development trends of the dominant species of plant communities was analyzed.The results were as follows:(1) According to the comprehensive and sequential classification which was founded by academician Pen Jizhou,it classifiedⅣA4- tepid and dry type(temperate desert grassland).According to the soil,terrain features,it was divided into three types of gravelly desert grassland,sandy desert grassland and saline desert grassland.(2) Gravelly desert grassland is located in erosible low hill and surrounding areas of northern Minqin.Saline desert grassland is mainly distributed in two sides of the lowest region of the West river and the East river and the ancient lake basin areas of northern Minqin;Sandy desert grassland is distributed as strip distribution between gravelly desert grassland and Minqin oasis.The overall features of Minqin desert grassland is sparse grassland vegetation,little plant types,poor quality and low yields.A total area was 934639.8 hm~2.The gravelly desert grassland and the sandy desert grassland in Minqin mainly accounted for 39.44%and 37.66%of the total area.(3) The representative communities of Minqin desert grassland are Nitraria community, Reaumuria community,Kalidium foliatum community,Phragmites australis community, Nitraria community,Leguminose community,Zygophyllum xanthaxylum community, Caragana community,Ephedraprzewalskii community and Potaninia mongolica maxim community.The large area of community is Nitraria community,310290.20 hm~2 and is 33.20%of Minqin desert grassland;The small area of community is Potaninia mongolica maxim community,8736.00 hm~2 and is 0.93%of Minqin desert grassland.(4) The number of features of plant community in Minqin desert grassland is a relatively small species number.The survey showed that the most species was Leguminose community and only 17 species,the least species was Phragmites australis community and only 5 species.The total plant species of Minqin desert grassland are 41 species.The number of species of various communities was rarely,the average appearance number of 16.67-66.67%plant species was less than 1 in sample area.Except for Phragmites australis community,other communities were mainly the dwarf shrubs,semi-bush. Analyse from the number of plants,Ephedraprzewalskii community,Potaninia mongolica maxim community,Kalidium foliatum community and Leguminose community,all were more than 90 percent;Among Reaumuria community,Caragana community and Zygophyllum xanthoxylum community,Nitraria community,the shrub layer was not dominance in the quantity,but herb layer was most of the smaller annual herb.(5) Except for Leguminose community and Zygophyllum xanthoxylum community,the important value of the dominant populations of other community was very prominent;In Ephedraprzewalskii community,important value of Ephedraprzewalskii was 159.78 higher than subdominant community,Zygophyllaceae.In Potaninia mongolica maxim community,important value of Potaninia mongolica maxim was 204.35 and was 160 higher than subdominant community,Zygophyllaceae.In Reaumuria community, important value of Reaumuria community was 134.5 higher than subdominant community, chinese wolfberry.In Kalidium foliatum community,important value of Kalidium foliatum was 179.84 higher than subdominant community,Zygophyllaceae.In Caragana community,important value of Caragana was higher than tangutica Nitraria, Zygophyllaceae and Leguminose and were 92.12,121.37and 112.98 respectively.Among Nitraria community and Phragmites australis community,important value of Nitraria and Phragmites australis account for the greater proportion.(6) The distribution pattern of dominant community of the plant community in Minqin desert grassland was clumped.This distribution pattern was connected with the population reproductive strategies,the population biological characteristics and the harsh habitat conditions.Ephedra przewalskii,Phragmites australis and Potaninia mongolica maxim formed a cluster distribution pattern of maternal plant as centre,kalidium foliatum, Reaumuria,leguminose,Caragana,Zygophyllum xanthaxylum and Nitraria population were mainly caused by the habitat condition.(7) The diversity index of all community in Minqin desert grassland was lower.The descending order of the diversity of nine kinds of community were Leguminose Community＞Phragmites australis Community＞Potaninia mongolica maxim Community＞Zygophyllum xanthaxylum Community＞Reaumuria Community＞Caragana Community＞Ephedra przewalskii Community＞Nitraria Community＞Kalidium foliatum Community.(8) From the appearance characteristics of plant community,the synusia structure of plant community in Minqin desert grassland was composed of simple herbaceous and shrub layer,and individual plants was dwarf,small crown,low biomass,with an average altitude of 0.60 m and lower than 1.00 m~2 crown;except for Nitraria,Zygophyllaceae and Caragana,the fresh weight of per plant biomass of most plant were below 1000 g / individual.(9) Analyzing from the age structure of advantage population of various community, Ephedraprzewalskii,Kalidium foliatum,Caragana,caragana opulens and Leguminose performed overall increasing;Zygophyllum xanthaxylum and Nitraria showed stable. Zygophyllaceae,Reaumuria and Potaninia mongolica maxim appeared decreasing.