Community Patterns In Tibet "three Rivers" River Of Desertified Land Ecological Recovery Process

In this thesis, we do research on the typical deserted land of Yarlung Zangbo River and Its Two Tributaries in Tibet, using the quad survey, selecting the area where has the same habitat conditions and the community development is more complete and human disturbance is relatively less to be the study sample lots.Using the important values to be quantitative traits and according to the color and the composition of plants of the communities, we type them; Using species richness,Shannon-Wiener diversity index,Pielou equality index and Simpson dominance index to measure and evaluate the species diversity.Using the diffusion coefficient C, negative binomial parameter (k), proliferation index (I), the average congestion ( m ~), poly block index ( m ~ /m) and Green's index (GI) and other indicators to determine the type of spatial distribution patterns of Sophora moorcroftiana populations on the conditions of different habitats.The research results show:In the research area, there are altitude plants of 26 species, 24 genera, 10 families and the most family is Gramineae, which accounts for 23.1%, followed by Asteraceae, Leguminosae and Chenopodiaceae.Communities in the study area in different seasons have different species composition-in May, there are only a small number of perennial herbaceous plants such as Orinus thoroldii,Artemisia wellbyi Hemsl.et Pears.ex Deasy,and Oxytropis hirta Bunge.and in September to October, the community has the largest species, the largest coverage and the most complex community structure.Associated with vegetation development and the process of community succession, species richness gradually increases and the important value of Chenopodium foetidum Schrad.is significantly enhanced during the process of community succession.Through the research of different types of community structures, we can see that the dominance of Pennisetum centrasiaticum Tzvel.and Orinus thoroldiiis gradually decreasing while the dominance of Chenopodium foetidum Schrad.and Eragrostis minor Hostis increasing, which shows that along with the gradual improvement of the sandy environment,the early dominant species gradually withdraw from the sandy environment, which is also reflected that in the process of natural recovery, the vegetation communities building of the arid valley of sandy plants have the process of growth and decline.Compared the two surveys of September 2007 and September 2008,we can find that the short-term banned can be quickly resumed the vegetation, but the community structure cannot be changed qualitatively.Measuring the species diversity of different types of communities shows that species richness (S) and Shannon-Wiener index (H ') reflects the consistent results.After the evolution of vegetation of the mobile dunes, semi-fixed sand dunes and fixing sand dunes, the diversity index (H '= 2.5951)of plant species is relatively high while the Shannon-Wiener index (H' = 2.4886) of mobile sand dunes is on the lower, and when the sand quality to the stage of gravel, Shannon-Wiener index increases with the succession of progress and to maintain relatively stable.Relative to the changes of species diversity , Simpson's index (D) and Pielou index (J)of community in the successional series of vegetation recovery decrease gradually, and when reach the stage of sandy gravel, to the lower value (J = 0.5955 , D = 0.7542), which shows that with the conduct of community succession, the composition and structure of community trend to stabilize.According to the results of classifying of plant height and crown of Sophora moorcroftiana populations, different types of Sophora moorcroftiana community populations have shown the phenomenon of lacking of tall plants and having more small and medium-sized plants; communities phase in different recovery, the individual patterns and population density of populations of Sophora moorcroftiana have the significant differences.Affected by soil moisture, nutrients, sand and interspecific competition and other factors, the growth rate of various biological indicators of in the early stage of community recovery is larger than the advanced stage.The results of the research of spatial distribution pattern of Sophora moorcroftiana population under the conditions of different habitats show that: different habitats of Sophora moorcroftiana populations have different spatial distribution patterns and the results of using six kinds of indicators to research the distribution patterns of Sophora moorcroftiana populations are basically the same, and different types of communities of Sophora moorcroftiana populations show varying degrees of aggregation distribution; with the progress of succession, the quantity of Sophora moorcroftiana populations is expanding while the gathered strength of distribution of population is declining.Environment is one of the definitive factors which form the spatial distribution patterns of the Sophora moorcroftiana populations.