Dissertation > Biological Sciences > Botany > Plant ecology and biogeography

Study on Plant Community Succession, Soil Erosion and Trend of Geomorphic Evolution in the Loess Hilly and Gully Resion

Author YangTao
Tutor WangDeXiang
School Northwest University of Science and Technology
Course Ecology
Keywords Loess Hilly area returning farmland vegetation succession soil erosion Geomorphic Evolution
CLC Q948
Type Master's thesis
Year 2009
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The study area was located in Mizhi Gaoxigou and Yan’an Shangbian valley, vegetation types in abandoned land and community characteristic was investigated with the method of space replacing time.This study also discussed vegetation succession and characteristics of soil erosion under different vegetation, its relationship with geomorphological changes was talked as well, the methods of artificial runoff plots and analysis of topographic maps at different stages was used . This study laid the foundation for the research of small watershed system development and soil erosion theory in Loess Plateau, and also provided scientific basis for the ecological environment and soil and water conservation. The main conclusions are as follows1. Through the sampling system and cluster analysis of plant communities, community structure and species diversity during succession was analyzed. The natural succession of plant community of abandoned land was divided into four stages.(1) Pioneer plant communities stage: The weed that had not been eliminated was considered as dominant species. When the cultivation was stopped, the weeds firstly occupy farmland and formed plant communities which Artemisia scoparia was dominant species. Subsequently, annual herbs gradually replaced weeds, Margalef species richness index, Simpson index increased, and Pielou index showed decreasing trends.(2) Stage of grass plant communities: As the vegetation succession went on, the space of pioneer species was gradually occupied by new species, and species diversity increased. Margate’s index showed an upward trend while Shannon-Wiener index had increased - reduced– increasing changing law, Pielou’s index had first increased and then decreased, this indicated that species competed fiercely for the resources and space during succession, finally formed the perennial herbaceous community.(3) Stage of Artemisia plant communities: with the increasing number of perennial herbaceous plants, Shannon-Wiener index and Simpson index first increased and then decreased, Margalef index showed decreasing trend of stability, which showed that the composition of species structure gradually became stable, dominant species was in more tend of relative stability. Palou’s index showed the same trend of slow increase, which indicated that distribution of species in returning land after vegetation restoration was in the balance. This stage showed the process of slow evolution of rosette herb community to shrub community.(4) Stage of shrub-grass and small tree: With the returning of land, emerged several herbs such as Lespedeza, Old World Bluestem community and drought tolerance undershrub. Shannon-Wiener index and Simpson index showed the law of increased - reduced– increasing style again, Margalef index decreased. Pielou’s index had first increased then decreased. Herb community gradually developed into shrub community, and Lespedeza community emerged, Agropyron cristatum was the dominant species in this stage in Mizhi Gaoxigou while Sophora viciifolia community emerged in Yan’an Shangbie valley. Plant Community Succession Sequence in Loess Hilly area was in this order Artemisia scoparia community→Aneurolepidium dasystachys community→Stipa bungeana community→Lespedeza davurica and Artemisa vestita community→Artemisa vestita and Sophora viciifolia community or Artemisa vestita and Sophora viciifolia community2. Based on the study of soil resistance to erosion under six different types of vegetation such as agricultural land, alfalfa, barren, black locust, Caragana and tabulaeformis, results showed that with the same rainfall, and basically the same gradient conditions, the impact of different vegetation types on soil resistance to erosion was significantly different, and soil resistance to erosion was in the order tabulaeformis> Peashrub> Locust> wasteland> alfalfa> agricultural land.3. By analyzing the relationship of Soil Erosion and Geomorphic Evolution of Baijiapan Basin Xigou in 1982 and 1997 .Draw the following conclusions:(1) soil erosion and landform Evolution varied in different gradient. The area of lanform was 36995m~2 in 1982, and 64954m~2in 1997.The area of landform less than 3°increased 27900m~2 in 1997 compared with 1982 , and when the gradient was between 3°~ 15°, the area reduced 9900 m~2 ,when the gradient was more than 15°, the area reduced 400 m~2. After more than ten years of soil erosion, the slope of gully edge was much fatter than that in gully bottom, and erosive soil of gully edge silted at the bottom of the basin made gully bottom become flat because of Sediment deposition.(2) Soil erosion and landform Evolution varied in different aspect. By using DEM Digital Elevation through analysis, sunny area in 1997 increased 7500 m~2 more than in 1982, while the area of shady slope decreased 4900 m~2. With the evolution of slope and erosion patterns of migration of substances, landform transformed between the sunny slope and shady slope in loess hilly region, mainly due to the impact of atmospheric circulation, rainfall at the time of the main wind direction, and rainfall-runoff etc.(3) Drainage area changed. Based on the DEM Digital Elevation methods, Drainage area increased 27957 m~2 more in 1997 than in 1982, which showed that rain caused serious soil erosion of golly edge from 1982 to 1997.

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