Studies On Population Ecology Of Artermisia Ordosica In Arid Regions

Artermisia ordosica is a fine semi—shrub for sand fixation in desert areas in China.Its ecological amplitude is relatively wide and there is widely distributed in arid and semi-arid region of China.The Ecology of desert vegetation which growing in the fragile ecology conditions is a research hotspot,but there are many research gaps in study of the Artermisia ordosica population ecology in arid region.Therefore,the study of Artermisia ordosica population ecology in arid region has great values in theory.For this reason,chose three Artermisia ordosica typical distribution area ,which are natural Artermisia ordosica distnbution area and haven't human disturbance.There are Shapotou Region in Ningxia province,Mingshazui in Gulang county and Caiqi in Minqin county in Gansu province.This paper investigates the following contentseses:(1) Community species composition and quantity characteristics of Artermisia ordosica ;(2) Size structure of Artermisia ordosica population;(3) Spatial distribution pattern of Artermisia ordosica population;(4) Intraspecific competition of Artermisia ordosica population;(5) Branching architectures of Artermisia ordosica plants, The main conclusions in this thesis have been summarized as follows.(1)From Shapotou to Mingshazui to Caiqi, with the precipitation gradually decreased, species richness gradually decreased. There are10 kinds species of vegetation in Shapotou,six kinds in Mingshazui, three kinds in Caiqi. From east to west, it showed a decreasing trend.In the study area,the most family of Artermisia ordosica community is Compositae(5 species),followed by Chenopodiaceae (4 species),Gramineae (3 species),Leguminosae (2 species),Polygonaceae, Tamaricaceae and Asclepiadaceae had one species.We can see from the important vales of the species in each sample that Artermisia ordosica population is the dominant species in the three study area and it played an important role in the communities.(2)Through analyzing the size structure of Artermisia ordosica population,the Artermisia ordosica population in Shapotou and Caiqi was in a stable stage,It showed the population adapted to local habitat conditions and was able to complete the natural regeneration under natural conditions.The Artermisia ordosica population in semi-fixed dune and fixed dune of Mingshazui was in a growth stage.It explained that the population in the zone can achieve maximize the expansion of their own survival by using the local environmental conditions. According to comparing the age structure of population in semi-fixed dune and fixed dune of Mingshazui,It was found that there was higher mortality rate during the period of young and middle age class in the semi-fixed dune ,but there were abundant trees of young and middle age class in the fixed dune.(3)The spatial distribution pattern types of Artermisia ordosica population in different regions of the study area were aggregation distribution.,but there is difference in the cluster size.the cluster size in different regions ranked in order of semi-fixed dune in Mingshazui ,fixed dune in Mingshazui,the plot in Shapotou and the plot in Caiqi.The results of pattern scale showed that the pattern scale of Artermisia ordosica population in Shapotou was 8m×8m.The the pattern scale of Artermisia ordosica population in the emi-fixed dune of Mingshazui was the same as the pattern scale in Shapotou. The Artermisia ordosica population in fixed dune of Mingshazui had two pattern scales which were 4 m×4m and 8 m×8m.The sampling area should be larger than 20m×20m when analysed the pattern scale of Artermisia ordosica population in Caiqi.(4)The intraspecific competition intensity of Artermisia ordosica gradually reduced with diameters scale increase.It could be interpreted that sizes of different individuals cause the different capabilities to occupy environmental resources. According to the different regions, the intraspecific competition intensity ranked in order of fixed dune in Mingshazui, the plot in Shapotou,semi-fixed dune in Mingshazui and the plot in Caiqi. Analyzing the reason of differences in intraspecific competition intensity,it should be comprehensively considered the impact of various environmental factors.(5)There is difference branching architecture of Artermisia ordosica plants between the different regions of the study area. The branch angle and branch length of Artermisia ordosica plants in Shapotou has an increase trend from outside to inside,but the ratio of branch diameter decreased first then increased; The branch angle of different branching level in Mingshazui had little difference,and it showed irregularly variety trend. The branch length increase first and then decrease from outside to inside,but the ratio of branch diameter decreases gradually. The branch angle of Artermisia ordosica plants in Caiqi has an decrease trend from outside to inside,but the branch length increase first and then decrease,and the ratio of branch diameter decrease first and then increase.Changing branched architecture is characteristic of Artermisia ordosica to adapt to drought,and obtaining more resources by adjusting the branch angle and length.The crown dimension and bifurcation dimension of Artermisia ordosica plants in the three different regions have been compared.The result is that the size of dimension ranked in Shapotou,Mingshazui and Caiqi.