| Ulmus pumila tree-dominated temperate savanna, distributed widely throughout the forest-steppe ecotone on the Mongolian Plateau, is a relatively stable woody-herbaceous complex ecosystem in northern China. Due to human irrational land use and the influence of global climate change, China’s temperate Savanna appeared widespread degradation or even disappears. And Ulmus pumila distribution areas, is not only a main hub of national minorities, but also the main ecological environment fragile zone, its existence in maintaining regional ecological system stability and biodiversity conservation has an irreplaceable role. More attention has been paid to the degradation of the typical steppe and less focus has been placed on the succession of this typical temperate savanna under the present management regime. So it is necessary to study the Ulmus pumila tree-dominated temperate savanna ecosystem structure and function, in order to provide the theory basis for the protection of this ecological system.Hence,we have laid the four experiments on the Otindag Sandy land,respectively were:experiment 1:25ha large Ulmus pumila Savanna fixed sample,by analyzing species composition, Isar and spatial distribution pattern of the fixed sample, structure and function of Ulmus pumila Savanna ecosystems were studied; experiment 2:Ulmus pumila Savanna magpie nests preference analysis, by a long line transects 1 Okm magpie nest site selection analysis, to explore the relationship between the bird and its surrounding habitat, provide the basis for conservation of temperate Savanna; experiment 3:Herbs Community Biodiversity and stability analysis of Ulmus pumila Savanna and artificial planting poplar; experiment 4 analysis composition and spatital pattern of Ulmus pumila Savanna under different grazing pressure gradient. The results show as follows:(1) We have found the vegetation 40 families and 195 species, about 30% of total Otindag Sandy land existing highe plants.Compositae is the most plant, followed by Gramineae. The population density of Ulmus pumila is 45.8 plants/ha, as following the population density of trees(DBH>20cm) is 10.3 plants/ha, the population density of trees(5<DBH<20 cm) is 19.6 plants/ha, the population density of trees(DBH<5cm) is 16 plants/ha., shrubs and herbs. Shrub had a positive effect on increasing the species diversity of the region, maintaining and promoting the regeneration of Ulmus pumila seedlings on Otindag Sandland. The diversity and stability of herbaceous plants in the Ulmus pumila Savanna was significantly better than that of the artificial poplar forest and with the increase of the density of Ulmus pumila Savanna sparse woods, the richness, evenness and diversity of herbaceous plants in the forest decreased.The Magpies are fond to build their nests at the top of a tall Ulmus pumila trees which periphery is sparse, open field of vision and close to the source of the forest. At the same time litter and dead Ulmus pumila trees are an important condition for the survival of the magpie population in the distribution area of the entire Ulmus pumila Savanna.(2) We found species promoting plant diversity occupied an absolute advantage in the community in Ulmus pumila Savanna ecosystem that was more obvious in small scale by the analysis of the spatial diversity pattern of different woody plants in the Ulmus pumila Savanna sparse woods. This spatial distribution pattern is significantly different from that of the temperate and tropical forests which proves that the interspecific interactions caused by the ecological niche differentiation determine the structure of the community diversity of Ulmus pumila Savanna and means that the neutral process does not dominate the construction process of the large scale community diversity. Ulmus pumila population showed aggregation distribution on a small scale, while the old and some middle age Ulmus pumila distributed evenly or randomly due to self thinning and other effects on the entire spatial scale. The positive correlation was shown between Ulmus pumila seedlings and middle age Ulmus pumila trees, while old Ulmus pumila and seedlings competed with each other.(3) Analysis of grazing pressure gradient on the spatial pattern of Ulmus pumila savanna showed the different types and structures of the shrubs were obviously changed by the different grazing pressure. With the increase of grazing pressure, the typical Ulmus pumila Savanna degenerated into drought shrub and sparse forest steppe with the coexistence of drought shrub and Ulmus pumila Savanna. In addition, the implementation of seasonal grazing management system, especially the application of the lawn after 2000a is the key to the update problems of the whole Ulmus pumila Savanna. |
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