| The artifical sand-fixing vegetation in Shapotou region, which is situated in southeast of Tengger Desert at Zhongwei county, Ningxia province, was taken as the object studied in this paper. The structures and dynamic changes of the artifical sand-fixing vegetation were studied based on the follow views: components of vegetation community, plant diversity, life-forms of vegetation, trends of plant growth, characteristics of the vertical and horizontal structure of vegetation, relationship between the vegetation community and environment(including soil moisture temperature etc.), relationship between the vegetation community and characteristics of plant physiological activities. Some results were showed as follow:1. Components, Diversity and Life Style of Artificial Vegetation in Shapotou RegionThe marked changes of artificial vegetation have taken place during more than 40 years, since the establishment of sand-fixing vegetation. The old sand dunes became the fixing-dune, the components of vegetation in the sand fixing region had increased from only a few species to more than 30 species with the time extending of sand-fixing vegetation. There were two stages with the obvious change velocity of plant species: the period of 15-25 years and the period of 40-50 years. The biological spectrum of vegetation in Shapotu region was not complete. It consisted of only three parts, including phanerophytes. therophytes hemicryptophytes, but lack of hemicryptophytes and cryptophytes.2. The Structure of Artificial Vegetation in Shapotou RegionThe structure of vegetation usually consisted of a vertical structureand a horizontal structure of vegetation. Based on the vertical structure of vegetation, there were three layers of artificial vegetation in Shapotou region. Those were shrubs' layer herbs' layer and microbiotic crusts layer. There were different species of vegetation in different layers. The species were separately Caragana korshinskii Hydysarum scoparim Artemisia ordosica in shrubs layer, Eragrostis poaeoides Bassia dasyphylla in herbs layer, Bryum argenteum Barbula ditrichodies in microbiotic crusts layer. And the dominant species of them were Artemisia ordosica Eragrostis poaeoides Bryum argenteum respectively.Due to the different time and the topographical varieties in the fixing-sand region, the horizontal structure of artificial vegetation manifested out the mosaic characteristics. The density and coverage of shrubs in vegetation had a negative correlation with the fixing-sand time, but those of herbs had a positive correlation. The results showed that the density and coverage of shrubs growing in the intervale of sand fixing region were biggest, but those of herbs were smallest. In contrast, the density and coverage of shrubs growing in the lee slope of dune were smallest, but those of herbs were biggest.3. The Growth Dynamic of Artificial Vegetation in Shapotou Region In Shapotou area, the growth curve of shrubs was like the form of "S". The stagnant period of growth was in April, the exponential period of growth was from May to July, the stable period of growth was from August to October. The plant growth stopped after October. The velocities of growth in shrubs were different in different sand fixing region. The growth of plants in the sand fixing region with a shorter time were faster than that with a longer time. This maybe directly resulted in the difference of the density and coverage of shrubs. Herbs bourgeoned with a high density and a low coverage in early July. With the coming ofrain season, the velocity of growth in herbs enhanced with the higher coverage in August. In September, the growth of herbs stopped and the density and coverage of herbs descended.4. Effect of Environmental Factors on the Structure of Vegetation The relationship between vegetative structure and environmentfactors (including soil moisture temperature etc.) was affinitive. Due to the low content of soil water in the sand-fixing area with a longer time, the growing velocity of shrubs decre... |
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