| The vegetation of Loess Plateau has been destroyed seriously. And the area is one of most fragile ecosystems in China. Severe desertification on the Loess Plateau as a result of improper land utilization has caused critical soil erosion and water shortages. To prevent further soil erosion, it is very important to cover the bare land surface with natural vegetation. Restoring the ecological balance is the main task to improve the region environment. Field survey and laboratory experiment were conducted to study changes of characteristics of the vegetation and soil seed bank in the fencing and grazing grassland on the loess plateau in typical prairie, to open out ecological significance of the vegetation and soil seed bank in degenerating and restoring succession series, which also could be regarded as a scientific basis for the rapid restoration of natural vegetation, and possessed reference meaning for other areas to restore natural vegetation. Main results were as follow:1 Stipa bungeana, S. grandis, Aneurolepidium dasystaehys, Artemisa vestita, Thymus mongolicus, Heteropappus altaicus and Elsholtzia ciliate were dominant and hypo-dominant species in Yuwushan Reservation in terms of higher important value than other species. The proportion of life form of the vegetation was: Perennial herbaceous plant>Annual herbaceous plant>Shrub. Comparing with the grazing measure, fencing had changed community structure remarkably, and notablely improved the number of species, the coverage, the height, the biomass and the diversity. Caragana microphylla had high important value in fencing grassland. The important value of A. vestita, Euphorbia fischeriana, A.dasystaehys, Potentilla acaulis, Carex rigescens and A. frigida were higher in grazing grassland than the fencing grassland.2 The characteristics of soil seed bank in Yunwushan Reservation were that: 37 species, which belong to 11 families germinated in the plots. In the species of seed bank, Gramineae, Compositea, Labiatae, Leguminosae and Panunculaceae occupied dominant positions; From spring to autumn, the percent of Leguminosae, Gramineae and Violaceae decreased, however, the percent of Compositea and Labiatae increased greatly; densities of the soil seed banks increased significantly; On the vertical distribution, the number of seeds took on a decreasing trend with the depth of soil increasing; The level distribution of soil seed banks followed the order of fencing>grazing, lunar slope > solar slope and top >middle > bottom; The results of the study indicated that the Margalef and the Shannon-Wiener diversity indexes of the soil seed banks were higher in the enclosed grassland, and Pielou evenness indexes were higher in the grazed grassland. From spring to autumn, they all decreased.3 The niche breadth of T. mongolicus, Dracocephalum heterophyllum and Androsace umbellate in soil seed bank reached more than 3.0, and we could said they were generation species of soil seed bank in Yunwushan Reservation. To some extent, what a degree of evenness of resources used by species was to decide the niche breadth. In the same resources space, there was no positive correlation between niche breadth and niche overlap of a species counterpart. The niche overlap was higher in the same class, which showed that, to a certain degree, the niche reflected genetic relationship between species far or close.4 In Yunwushan Reservation,fencing measure, the soil water of 0~20cm depth, slope direction and slope level were dominant factors affecting species distribution. The influence order was: slope direction> fencing measure =the soil water of 0~20cm depth> slope level. 5 The species similarity of the vegetation and soil seed bank was low in Yunwushan Reservation. In fencing plot, the species similarity of the vegetation and soil seed bank was higher than in grazing plot.
|
PDF Full Text Request